Sprinting


Sprint running is an important quality for many athletes. It can be subdivided into accelerating sprint running and constant-speed sprint running. Track athletes appear to accelerate for longer distances (50 – 60m) than team sports athletes (20 – 30m) but may not necessarily accelerate maximally.

Many training methods can increase sprinting speed in athletes, including conventional sprint running training, resisted sprinting, resistance training, ballistic training, plyometrics, and a combination. Comparisons of these training methods have not yet identified which is best and training status may affect the selection of the best method.

Resistance training is effective for increasing sprinting speed in athletes and the squat is the most commonly-explored resistance training exercise. Increases in squat strength are strongly associated with improved sprinting speed. However, using lighter loads and faster bar speeds during resistance training does not appear to produce better results than heavy loads and slow bar speeds and the effect of exercise selection is unclear.

Resisted sprinting is effective for improving sprinting speed in athletes and sled towing is the most common type resisted sprinting method. Contrary to popular belief, the weight of the sled appears to have little influence on outcomes and both heavy and light sled loads can be used successfully.

Plyometrics are effective for improving sprinting speed in athletes. No single plyometrics exercise has been shown to be more effective than any other, although a variety appears to be better than one exercise alone.

Owing to differences in measurement methods, sprint times measured using manual and electronic systems should not be compared with one another. Sprint times measured using different systems or using different settings within individual systems should not be compared with one another.

As they display superior reliability, electronic timing systems should be used in preference to manual timing systems where possible. The exact parameters used within electronic timing systems (gate position and photocell vs. pressure sensors) and stance do not appear to affect reliability.

Longer sprint distances up to 20m are likely more reliable than shorter distances (5 – 10m). Whether sprint distances >20m are more reliable than 20m sprint distances is unclear. Using a flying start for 10m or 20m may enhance reliability. Although electronically-measured sprint times are reliable, large SEM and MD values make inferring differences between athletes or improvements difficult.

CONTENTS

Full table of contents

Click on the links below to jump down to the relevant section of the page:

Background

Reliability

Sprinting

Resisted sprinting

Resistance training

Plyometrics

Ballistic training (including Olympic weightlifting)

Combined training

Comparisons of training methods

Biomechanics of sprinting

Training transfer

References


BACKGROUND TO SPRINTING

PURPOSE

This section sets out the background to training for sprinting and explains the different measurements of sprint running ability.

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BACKGROUND

Introduction

Sprint running has been reviewed comprehensively by many researchers over the years (e.g. Mero et al. and Mann), and specific aspects of sprint running have also been reviewed in some detail, including kinematics (e.g. Mann, 1986) kinetics, (e.g. Mann, 1981; Mann and Sprague, 1983) ground reaction forces (e.g. Randell et al. 2010), stiffness (e.g. Brughelli and Cronin, 2008a; Brughelli and Cronin, 2008b), electromyographic (EMG) activity (Schache et al. 2014), and the transfer of training to sprint running in respect of ground reaction forces (e.g. Randell et al. 2010), strength (Cronin et al. 2007; Seitz et al. 2014) and power (Young, 2006; Triplett et al. 2012). This page provides an integrated overview of all of these training, kinematic, kinetic, stiffness and EMG activity research studies. As noted above, the training studies have been limited to those performed in athletic subjects, while the biomechanics analyses include subjects from a range of different populations.

Different modes of gait

Walking, running and sprint running are all modes of gait. They share common features but also display differences. The fundamental difference between walking and running (and sprint running) is that walking always has one foot in the stance phase while the other foot is in the swing phase. In contrast, running (and sprint running) display a stance phase while one foot is on the ground and a swing phase in which both feet are off the ground. Humans naturally transition from walking style of gait to the running style of gait once they reach a certain speed. The transition from walking gait to running gait seems to occur at around 2.0 – 2.7m/s (see review by Schache et al. 2014). The difference between running and sprint running is much less clear. At constant speeds, sprint running might be most easily defined as running at maximal speed. During periods of acceleration, this may be an oversimplification, as explained below.

Different types of running

Both running and sprint running can be subdivided into two important sub-categories: accelerating or constant-speed running (or sprint running). Constant speed running is frequently studied in the literature, typically in order to understand the differences in biomechanics (such as ground reaction forces or muscle activity) between running at two different speeds (e.g. 4m/s and 6m/s). Accelerating running is less frequently studied but is sometimes investigated and involves measuring changes in biomechanical variables as runners accelerate from one sub-maximal speed (e.g. 4m/s) to another (e.g. 6m/s). Sprint running is most commonly assessed either over very short distances of maximal accelerating sprints (e.g. 5m, 10m or 20m) or over similar very short distances of maximal constant speed sprint running (e.g. 10m following a 30m flying start). While it is often assumed that all accelerating sprints are performed with maximal effort and acceleration, this is probably not the case, as many world-class sprinters have achieved substantially faster times in 60m races than they record as 60m splits in 100m races (see review by Brown and Vescovi, 2012; see data by Koyama et al. 2011). This makes differentiating between maximal accelerating sprint running and accelerating high-speed running highly problematic. As a general rule of thumb, it has been suggested that sprint running performance can be divided into three different phases in team sports athletes: accelerating (0 – 10m), attaining maximum speed (10 – 36 m), and maintaining maximum speed (36 – 100m) (see review by Hrysomallis, 2012).

Different types of athletes

Track sprinters require the ability to sprint in the shortest possible time over their set distance as determined by their event (60m, 100m, 200m, or 400m). However, team sports athletes require the ability to sprint over a far more variable set of distances, most of which are generally far shorter. For example, Vescovi (2012) reported that the average sprint distance covered by professional female soccer players during competitive matches was 15.1 ± 9.4m and Andrzejewski et al. (2013) observed that 90% of sprints performed by professional soccer players were <5 seconds in duration. Nevertheless, this does not mean that team sports athletes only require the ability to perform accelerating sprints and do not require the ability to perform maximum, constant speed sprint running. In fact, although track sprinters do accelerate continuously through at least 50m (Nagahara et al. 2014a; Nagahara et al. 2014b), it has been shown that team sports athletes typically reach maximum velocities in short distances of around 20 – 30m, in contrast to track athletes who accelerate for much longer distances (see review by Brown and Vescovi, 2012).

CONCLUSIONS REGARDING SPRINTING

Sprint running is an important quality for many athletes. It can be subdivided into accelerating sprint running and constant-speed sprint running. Track athletes appear to accelerate for longer distances (50 – 60m) than team sports athletes (20 – 30m) but may not necessarily accelerate maximally.

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RELIABILITY

PURPOSE

This section details the test-re-test reliability of sprint times, which helps provide strength and conditioning coaches with a method for assessing whether an improvement in a sprint performance is real or random.

BACKGROUND

Introduction

When using tests, it is important to be certain that they are both reliable and valid. When a test is reliable, this means that it routinely produces the same result (output) for the same performance (input). When a test is valid, this means that it actually measures what it is supposed to measure. Tests can display very good reliability and poor validity and vice versa. Reliability is much easier to measure than validity for tests and screens and therefore there are usually more studies for any given test or screen for reliability than validity. Reliability can be measured in at least two, if not three ways: inter-rater reliability, intra-rater reliability, and test-re-test reliability. Each of these contribute to our overall assessment of the reliability of a test but test-re-test reliability is the most important for strength and conditioning coaches.

Test-re-test reliability

Test-re-test reliability refers to the extent to which an individual will perform similarly on the same test on multiple, similar occasions. It is occasionally, albeit incorrectly referred to as intra-rater reliability. True intra-rater reliability can sometimes be differentiated from test-re-test reliability and sometimes it cannot. True intra-rater reliability can be tested when we are certain that the underlying outcome is truly identical in both cases. For example, when a movement screen is tested by a rater watching the same video of a screening performance on two separate occasions, this is true intra-rater reliability. Test-re-test reliability differs from true intra-rater reliability, as it involves the outcome being measured again shortly after the initial test. For example, when a movement screen is tested by raters watching a person perform the screen on two separate (live) occasions, this is test re-test reliability. It includes variability inherent in the individual performance as well as in the rater assessment. Consequently, test-re-test reliability is normally worse than true intra-rater reliability.

Intra-class correlation coefficients

There are three main ways to measure reliability, of which the intra-class correlation coefficient (ICC) is one. The ICC measures the amount of variance that arises from measuring different individuals vs. measuring the amount of variance that arises from measuring multiple occasions. A high ICC means that most of the variance seen in a data set is caused by the differences between individuals. A low ICC means that most of the variance is seen between multiple tests. In practice, the size of an ICC will depend on the desired accuracy of the outcome and the between-individual variability in the population being tested. However, in practice, typical standards used are as follows:

  • Trivial (r < 0.1)
  • Small (r = 0.1 – 0.3)
  • Moderate (r = 0.3 – 0.5)
  • Good (r = 0.5 – 0.7)
  • Very good (r = 0.7 – 0.9)
  • Nearly perfect (r > 0.9)

Standard Error of Measurement (SEM)

There are three main ways to measure reliability, of which the Standard Error of Measurement (SEM) is one. Although the ICC is the most common, the SEM is probably more useful. The SEM converts the ICC into a usable format for comparing the performances of several individuals in practice (for exact method and rationale, see review by Weir, 2005). The SEM is essentially the typical error that can arise when recording the score of a test. When taking a single measurement, the SEM can be used to construct a confidence interval (usually a 95% confidence interval) on either side of the measured value. This confidence interval provides an approximation of the range in which the real value will fall, either side of the measured value. The most commonly-used estimate of the SEM uses the standard deviation (SD) as follows: SEM = SD x √(1-ICC) and this has been used to estimate SEM in this section where the researchers have not performed any calculation themselves (see further review by Weir, 2005). This estimate of the SEM is similar, if not identical, to the typical error (TE) proposed by Hopkins (2000).

Minimum Difference (MD)

There are three main ways to measure reliability, of which the Minimum Difference to be considered real (MD) is one. Unlike the SEM, there is no commonly-accepted terminology for the MD and it is also sometimes called the Smallest Real Difference (SRC), Smallest Worthwhile Change (SWC) or Smallest Detectable Difference (SDD), depending on the main influences of the authors reporting a study. Although the ICC is the most common, the MD is a way of converting reliability measurements as recorded using ICCs into a usable format for comparing the results of a single individual on multiple occasions, such as before and after a training program (for exact method and rationale, see review by Weir, 2005). Thus, while the SEM deals with differences between subjects, the MD addresses differences within the same subject. When calculated in a traditional way, the MD is always larger than the SEM because it involves two possible errors from two measurements rather than a single error from one measurement. The standard approach to calculating the MD is similar to the SEM and involves estimating a confidence interval. This confidence interval around the MD is most commonly estimated as ±(SEM x 1.96 x √2) (see further review by Weir, 2005). Since the MD is generally quite large for most performance tests, this limits the ability of coaches to monitor improvements in athletic performance for individual athletes. Consequently, different approaches have been proposed that reduce it. Such modifications include multiplying the MD by factors such as 0.2, 0.3 and 0.5 times (Hopkins et al. 1999; Hopkins, 2005; Hopkins, 2011; Malcata and Hopkins, 2014) or calculating the MD based on other data, such as the coefficient of variation (COV) within athletes across multiple individual performances (Hopkins, 2005).

Coefficient of Variation (COV)

Between athletes

Although there are three main ways to measure reliability (ICC, SEM and MD) the coefficient of variation (COV) is also sometimes reported. Most commonly, the COV is simply calculated as a relative measure of the standard deviation (SD) of all performances in a group of athletes with respect to the mean (M) of the same performances, expressed as a percentage (SD/M x 100). When using this method of calculation, the COV simply provides a measurement of how broadly spread the performances of all athletes are relative to the mean performance. Tests performed in a more general population will necessarily therefore display a large COV and tests performed in a group of athletes will display a small COV. The usefulness of this metric is therefore limited for assessing the ability of a test to identify improvements in a single athlete.

Within athletes

The COV can also be calculated within athletes, by measuring the relative measure of the standard deviation of single athletes across multiple performances, expressed as percentage of the mean (Hopkins, 2005; Malcata and Hopkins, 2014; Haugen et al. 2014a). This provides a measure of variability for a single athlete and consequently gives an indication of how likely an athlete is to perform close to their real underlying ability on every occasion. In reviewing track and field running events <3km in distance, Hopkins (2005) calculated that the COV within athletes was around 1.0% (CI = 0.9 – 1.1%), although noting that this variability was slightly greater in females than in males and increased with increasing time between competitive performances. Based on this calculation, a smallest worthwhile change (SWC) of 0.3 – 0.5% was suggested for short distance running events in competitive track athletes, being 0.3 – 0.5 times the COV within athletes (Hopkins, 2005). Whether this can be applied to team sports athletes performing sprint tests over 5 – 40m is unclear. Haugen et al. (2014a) reported that when testing 20m sprint times in soccer players across 6 separate sprints in a single testing session, the COV within athletes was 0.025 seconds (0.8%). However, the COV across multiple testing sessions in a group of athletes not receiving any specific intervention for improving sprinting performance was much greater, at 0.06 seconds (2.0%).

RELIABILITY OF SPRINT TIMES

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing the reliability of sprint times between 5 – 40m, using any timing method in adult subjects

Comparison – between sessions (test-re-test reliability), between types of starting stance, between distances

Outcomes – Pearson’s correlation coefficient, Standard Mean Difference (SMD), Minimum Difference to be considered real (MD), or Coefficient of Variation (COV)

Results

The following relevant studies were identified that met the inclusion criteria: Haugen (1999), Duthie (2006), Cronin (2007a), Cronin (2008), Ebben (2009), Enoksen (2009), Hopker (2009), Mayhew (2010), Lockie (2013), Haugen (2014), Mann (2015), Haugen (2015).

Findings

COMPARISON OF MANUAL AND ELECTRONIC TIMING SYSTEMS: SPEED

Timing systems can be divided into manual and electronic types. Manual systems are typically those involving operated hand-held stopwatches. Electronic timing systems make use of a variety of techniques. In practice, these can be divided into those that use photocells that the athlete breaks as they pass through a timing gate and pressure pads that an athlete lifts their foot or hand off prior to commencing the start of the sprint. Comparing manual and electronic timing systems, Ebben et al. (2009) reported that manual systems were around 6.4% and 5.3% faster, in the 20 yard and 40 yard sprints, respectively. Similarly, Mayhew et al. (2010) found that manual timekeeping was 6.4% faster in the 40 yard sprint compared to an electronic timing system. And Mann et al. (2015) found that manual systems were around 4.5 – 5.3% faster in the 40 yard sprint across experienced and novice timekeepers compared to an electronic timing system. These studies indicate that times measured using manual and electronic systems should not be compared with one another.

COMPARISON OF MANUAL AND ELECTRONIC TIMING SYSTEMS: RELIABILITY

Comparing manual and electronic timing systems, Ebben et al. (2009) reported that manual systems seemed to have greater COV than electronic systems, in the 20-yard (1.37 vs. 0.62%) and 40-yard sprints (0.96 vs. 0.56%), respectively. Mayhew et al. (2010) reported that manual timekeeping was consistently lower in reliability than electronic timing, as measured by ICC (ICC = 0.904 – 0.971 vs. 0.982) but the findings were not statistically significant. Mann et al. (2015) compared manual timing using stopwatches in both experienced and novice timekeepers with electronic timing gates and found that the electronic timing system was slightly more reliable, as measured by the MD (0.12 vs. 0.14 seconds). These findings suggest that electronic timing systems should be used in preference to manual timing systems where possible.

EFFECT OF ELECTRONIC TIMING SYSTEM METHODS: SPEED

Comparing the position of the gates when using the same electronic timing system involving photocells, Cronin and Templeton (2008) compared the effects of setting up the timing gates at either 60cm or 80cm from the ground. They found that the low gate position recorded a faster time than the high gate position at both 10m and 20m (by around 0.07 seconds). Haugen et al. (2014) found that 40m sprint times triggered by breaking a photocell beam from a standing start and by the front foot release from the ground in a standing start were 0.27 and 0.69 seconds faster than a block start, respectively. These studies indicate that times measured using different electronic methods should not be compared with one another.

EFFECT OF ELECTRONIC TIMING SYSTEM METHODS: RELIABILITY

Comparing the position of the gates when using the same electronic timing system involving photocells, Cronin and Templeton (2008) found little difference between low and high gate positions, either for 10m (1.1 vs. 1.2%) or 20m (0.69 vs. 0.83%). Haugen et al. (2014) compared the reliability of 40m sprint times with the same stance (a standing start) using two different electronic timing methods: (1) triggering the start by breaking a photocell beam, and (2) triggering the start by front foot coming off a pressure pad on the ground. They found that both methods were all similarly reliable. These studies indicate that so long as the same settings are used, various possible methods within electronic systems are acceptable.

EFFECT OF STANCE ONLY: SPEED

Some studies have identified the way in which stance affects the time recorded during sprints. Cronin et al. (2007a) compared 3 different standing starts in which timing was activated by passing the first gate: parallel (feet parallel to the start line), split (lead left foot on start line, right leg back), and false (initial parallel start, right leg drops back to split start when movement initiated). Cronin et al. (2007a) reported that the parallel start was slower than both the other two stances for both 5m and 10m sprint distances. Johnson et al. (2010) compared four difference stances: parallel (feet evenly placed with toes behind the line), false start (feet started in a parallel stance with toes behind the line then began by stepping back with the preferred foot before stepping forward with the front foot), staggered (feet started with preferred foot forward and toes behind the line then began by stepping forward with the back foot), staggered false start (feet started in a staggered stance with preferred foot forward and toes behind the line then began by switching feet before stepping forward with the front foot). They found that the false start, staggered and staggered false starts were all faster than the parallel start and the staggered false start was faster than the false start. These studies suggest that starting sprint stance should be carefully controlled between trials to ensure that comparability exists between tests.

EFFECT OF STANCE AND METHOD: SPEED

Some researchers have compared the effects of changing both stance and method in combined conditions. Duthie et al. (2006) compared 3 different starts, of which 2 were standing: a standing start in which timing commenced when the first photocell gate was activated (photocell gate), a standing start with timing activated when the front foot left a pressure sensor (pressure sensor), and a conventional 3-point start that was activated when the thumb left a pressure sensor (3-point start). The starts were fastest in the order: 3-point > standing (photocell gate) > standing (pressure sensor). Similarly, Haugen et al. (2012) compared the 40m sprint times between a gunfire-triggered start from a block with automatically-triggered start stances: a 3-point start (pressure sensor), a standing start (photocell gate), and a standing start (pressure sensor). They also found that the 3-point start, standing (photocell gate) and standing (pressure sensor) sprint times were 0.17, 0.27, and 0.69 seconds faster than the block start. These studies suggest that starting sprint stance and method should be carefully controlled between trials to ensure that comparability exists between tests and that the 3-point stance is likely preferable if close comparison with a block start is required.

EFFECT OF STANCE: RELIABILITY

Some studies have identified the way in which stance affects the reliability of recording sprint times. Cronin et al. (2007a) compared 3 different standing starts in which timing was activated by passing the first gate: parallel (feet parallel to the start line), split (lead left foot on start line, right leg back), and false (initial parallel start, right leg drops back to split start when movement initiated) and found no differences between conditions. Duthie et al. (2006) compared 3 different starts, of which 2 were standing: a start in which timing commenced when the first gate was activated (standing start), a standing start with timing activated when the front foot left a fixed timing mat (standing foot start), and a conventional 3-point start using a thumb switch to commence the timing (thumb start). Duthie et al. (2006) did not consider that there was any difference in reliability between the stances but the foot start displayed a lower ICC compared to the other two starts, suggesting that the standing or 3-point starts might be preferable. Haugen et al. (2014) compared the effects of a block start, a 3-point start and a standing start on 40m sprint times. They found that all stances were similarly reliable.

EFFECT OF FLYING START DISTANCE: RELIABILITY

Some studies have identified the way in which stance affects the reliability of recording sprint times. Haugen et al. (2015) measured the reliability of both 10m and 20m sprint times with 0.5, 1, 1.5, 2, 5, 10 and 15m flying starts, recording times using electronic timing gates. Test-retest reliability for 20m sprint times was very high (ICC = 0.99) for all flying start distances (0.5 – 15m) but increased with increasing flying start distance. For example, the 0.5m flying start displayed SEM and COV of 0.03 seconds and 1.2% while the 15m flying start displayed SEM and COV of 0.02 seconds and 0.9%. Haugen et al. (2015) noted that 10m sprint times displayed a similar trend.

EFFECT OF SPRINT DISTANCE: RELIABILITY

Some studies have explored the extent to which distance tested affects the reliability of sprint times. In general, shorter distances (<20m) seem to display worse reliability than longer distances (>20m). This is most clearly seen in Lockie et al. (2013), where the reliability of sprint testing over 5m, 10m and 20m was reported. Reliability increased with increasing sprint distance (ICC = 0.76, 0.85, 0.96). Similarly, Cronin et al. (2007a) compared the COV across 5m and 10m sprint times and found that COV was lower in the 10m than in the 5m sprint (1.16 – 1.67% vs. 1.43 – 2.15%). Similarly, Cronin and Templeton (2008) compared the COV across 10m and 20m sprint times and found that COV was lower in the 20m than in the 10m sprint (0.69 – 0.83% vs. 1.1 – 1.2%). Ebben et al. (2009) compared the COV between 20-yard and 40-yard sprint times and found that COV tended to be lower for the 40-yard than for the 20-yard sprint times (0.56 – 0.96% vs. 0.62 – 1.37%). And Haugen et al. (2015) found that COV was lower in the 20m sprint (0.9 – 1.1%) than in the 10m sprint (1.4 – 1.8%). However, when Enoksen et al. (2009) compared the COV over 20m and 40m sprints using the Newtest powertimer electronic timing system, there was little difference between distances (3.67 vs. 3.74%). This may indicate that the 20m sprint is the best option for measuring short distance sprint running ability reliably.

INTRA-CLASS CORRELATION COEFFICIENTS: <20m

The test-re-test reliability of short-distance (<20m) sprint times as measured by ICC has varied. For 5m sprint times, Chelly et al. (2009) noted in passing that reliability was very good (ICC = 0.82) and Lockie et al. (2013) also found that reliability was very good (ICC = 0.76). For 10m sprint times, Duthie et al. (2006) reported that test-re-test reliability was very good (ICC = 0.86) using the foot-operated standing stance and nearly perfect (ICC = 0.92) using either the photocell-operated standing or 3-point stances. Lockie et al. (2013) similarly found that reliability was very good (ICC = 0.85). In passing, Bachero-Mena and González-Badillo (2014) noted that reliability was very good (ICC = 0.87) and Haugen et al. (1999) reported similar findings (ICC = 0.77).

INTRA-CLASS CORRELATION COEFFICIENTS: >20m

The test-re-test reliability of longer-distance (>20m) sprint times as measured by ICC has most often been reported as nearly perfect. For 20m sprint times, Lockie et al. (2013) reported that reliability was nearly perfect (ICC = 0.96). Haugen et al. (1999) also reported that reliability was nearly perfect over the same distance (ICC = 0.90) while Haugen et al. (2015) most recently reported nearly perfect reliability (ICC = 0.99). For 40 yard sprint times, Mayhew et al. (2010) reported that reliability was nearly perfect when using electronic timing (ICC = 0.98) and when using manual timekeeping (ICC = 0.90 – 0.98). For 40m sprint times, Rimmer and Sleivert (2000) reported in passing that reliability was nearly perfect (ICC = 0.94 – 0.98). Similarly, Haugen et al. (2014) reported that the test-re-test reliability was nearly perfect (ICC = 0.97 – 0.99) irrespective of whether a block, 3-point, or standing stance (either foot-operated or photocell-operated) was used.

STANDARD ERROR OF MEASUREMENT (SEM): <20m

Estimating the real differences in sprint running ability over distances <20m between two or more athletes is extremely difficult, given the large size of the SEM. Lockie et al. (2013) reported that the SEM for a 5m sprint was 0.04 seconds (4.2%) and that the SEM for a 10m sprint was also 0.04 seconds (2.1%). Haugen et al. (1999) similarly reported that the SEM for a 10m sprint was 0.03 seconds (2.0%). These studies imply that differences in times of approximately 0.04 seconds or between 2 – 4% are likely necessary to identify a real difference between multiple athletes in sprints <20m.

STANDARD ERROR OF MEASUREMENT (SEM): >20m

Estimating the real differences in sprint running ability over distances >20m between two or more athletes is extremely difficult, given the large size of the SEM. For a 20m sprint, Lockie et al. (2013) reported that the SEM was 0.04 seconds (1.1%) and Haugen et al. (1999) also reported 0.04 seconds (1.2%). However, Haugen et al. (2015) more recently reported 0.03 seconds (1.0%) when using an 0.5m flying start and 0.02 seconds (0.8%) when using a 15m flying start. For 40 yard sprints, Mayhew et al. (2010) reported that the SEM was 0.04 seconds (0.7%) when using electronic timing and 0.04 seconds (0.8%) when using manual timekeeping. With an almost identical finding, Mann et al. (2015) reported that the SEM was around 0.05 seconds (1.0%) but this did not depend substantially on whether manual or electronic timing was used. For 40m sprints, Haugen et al. (2014) reported that the SEM was 0.04 – 0.06 seconds (0.7 – 1.1%), depending on the starting stance/method used for the measurement. These studies imply that differences in times of approximately 0.05 seconds or around 1% are likely necessary to identify a real difference between multiple athletes in sprints >20m.

MINIMUM DIFFERENCE TO BE CONSIDERED REAL (MD): <20m

Estimating the real improvement in sprint running ability over distances <20m for an athlete is extremely difficult, given the size of the MD. For 10m sprints, Duthie et al. (2006) reported that the MD was 0.02 seconds (1.3%), irrespective of the starting stance used but did they not provide supporting information to support the calculation. Based on the SEM reported by Lockie et al. (2013), the MD can be estimated as 0.11 seconds (5.8%) and based on the SEM reported by Haugen et al. (1999), a very similar MD of 0.09 seconds (5.6%) can be calculated. Nevertheless, the picture for 5m sprint times appears even worse, with an MD calculated based on the SEM reported by Lockie et al. (2013) of 0.12 seconds (11.5%), which is clearly unusable in practice. Identifying improvements using a standard MD over distances <20m therefore appears to be very difficult, as the most promising MD seems to be around 0.1 seconds (6%) for 10m sprints, which is still very large.

MINIMUM DIFFERENCE TO BE CONSIDERED REAL (MD): >20m

Estimating the real improvement in sprint running ability over distances >20m for an athlete is also extremely difficult, given the size of the MD. For 20m sprints, Hopker et al. (2009) reported that the MD with a walking start was 0.12 seconds (3.5%) but whether this finding can be extrapolated to a standing or 3-point start is unclear. Based on the SEM reported by Lockie et al. (2013), an MD of 0.10 seconds (3.1%) can be calculated and based on the SEM reported by Haugen et al. (1999), an identical MD of 0.10 seconds (3.2%) can be calculated. The picture presented by Haugen et al. (2015) when using flying starts is slightly better, with MD ranging between 0.06 and 0.08 seconds (2.2 – 2.6%). For 40 yard sprints, Mann et al. (2015) reported an MD of 0.12 – 0.14 seconds (2.3 – 2.9%), depending on whether manual or electronic timing was used. For 40m sprints, based on the SEM reported by Haugen et al. (2014), an MD can be estimated as 0.11 – 0.17 seconds (1.9 – 2.9%), depending on the starting stance/method used in the trial. Identifying improvements using a standard MD over distances >20m therefore appears to be slightly less difficult than for distances <20m, as 20m sprints display an MD of around 0.10 seconds (3%) and 40m sprints a similar MD of around 0.15 seconds (3%).

COMPARISONS OF MD WITH ACTUAL IMPROVEMENTS: <20m

Some studies have reported actual changes in 10m sprint times following training interventions. In recreationally-trained males, the improvement in 10m sprint times over a 6 – 8-week program is approximately 1.0 – 5.3% (Dawson et al. 1998; Rimmer and Sleivert, 2000; Tricoli et al. 2005; Zafeiridis et al. 2005; Lockie et al. 2012). In athletes, the improvements are generally slightly smaller (1.1 – 3.2%), albeit still substantial (Harris et al. 2000; Ronnestad et al. 2008; Helgerud et al. 2011). Nevertheless, it is unclear whether such large changes are larger than the MD, which seems to be around 0.1 seconds (6%) for 10m sprints.

COMPARISONS OF MD WITH ACTUAL IMPROVEMENTS: >20m

Some studies have reported actual changes in 40m sprint times following training interventions. In recreationally-trained males, the improvement in 40m sprint times over a 6 – 8-week program seems to range from approximately 1.3 – 2.6% (Wilson et al. 1996; Murphy and Wilson, 1997; Dawson et al. 1998; Rimmer and Sleivert, 2000). In athletes, the improvement seems to be smaller (0.8 – 1.9%) over a similar, or slightly longer period (Majdell and Alexander, 1991; Lyttle et al. 1996; Ronnestad et al. 2008; Ronnestad et al. 2011). Nevertheless, it is unclear whether such large changes are larger than the MD, which seems to be around 0.15 seconds (3%) for 40m sprints.

CONCLUSIONS REGARDING SPRINTING

Owing to differences in measurement methods, sprint times measured using manual and electronic systems should not be compared with one another. Similarly, sprint times measured using different electronic systems or when using different settings within individual electronic systems should not be compared with one another.

As they display superior reliability, electronic timing systems should be used in preference to manual timing systems where possible. The exact parameters used within electronic timing systems (gate position and photocell vs. pressure sensors) and stance do not appear to affect reliability.

Longer sprint distances up to 20m are likely more reliable than shorter sprint distances (5 – 10m). However, whether sprint distances >20m are more reliable than 20m sprint distances is unclear. Using a flying start for 10m or 20m may enhance reliability.

Although electronically-measured sprint times over all distances are extremely reliable, large SEM and MD values make inferring differences between athletes or changes following training very difficult.

Differences of around 0.04 seconds or 2 – 4% are likely necessary to identify a real difference between multiple athletes in sprints <20m, while differences of around 0.05 seconds or 1% are likely necessary to identify a real difference between multiple athletes in sprints >20m.

Differences of around 0.1 seconds (6%) for 10m sprints, around 0.1 seconds (3%) for 20m sprints, and around 0.15 seconds (3%) for 40m sprints are likely necessary to identify a real improvement for a single athlete.

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SPRINT RUNNING TRAINING FOR SPRINTING

PURPOSE

This section sets out the extent to which sprint running is effective for improving sprinting speed in either recreationally-trained or highly-trained adult athletes.

BACKGROUND

Introduction

Sprinting is the most specific type of training that can be performed for improving sprinting speed. Therefore, on the basis that specificity is a key strength and conditioning principle, it might reasonably be assumed that this type of training is the most effective.

Mechanisms of action

Sprint running has been widely recognised as a highly effective training method for improving sprinting speed by athletes and coaches, most probably since the dawn of the Olympic games. It is likely that sprint running training improves sprinting speed by a number of different mechanisms. The most probable mechanisms include increases in velocity-specific force production or superior motor coordination in the sprint running movement.

META-ANALYSES

Recreationally-trained athletes

Few meta-analyses or systematic reviews have analysed the benefits of sprint running training on sprint running performance. Rumpf et al. (2014) performed meta-analyses regarding the effects of various types of training modality for improving sprint running performance in recreational athletes. Firstly, they grouped training methods into specific (sprinting or resisted sprinting) and non-specific (plyometrics, resistance training, and ballistic training). They noted that both specific and non-specific training methods were similarly effective in recreational athletes for improving sprint running speeds. This indicates that sprint running training is likely effective for improving sprint running performance in recreationally-trained athletes. However, this meta-analysis was limited as not all of the identified studies presented data in a format suitable for combining into an overall effect size. Different results might have been observed if these studies had disclosed this information. Also, many of the studies included that were classified as being performed in “recreational athletes” were performed in physical education students and it was not clear from the details included in the individual studies that they were all also competitive athletes at some level. This meta-analyses in this part of the investigation by Rumpf et al. (2014) may therefore include some groups that were relatively untrained.

Highly-trained athletes

As noted above, sprint running training can improve sprint running ability in recreationally-trained athletes. The picture is similar in highly-trained athletes, although this group may benefit to a greater extent. Rumpf et al. (2014) performed meta-analyses regarding the effects of various types of training on sprint running performance in highly-trained athletes. Firstly, they grouped training methods into specific (sprinting or resisted sprinting) and non-specific (plyometrics, resistance training, and ballistic training). They found that both specific and non-specific training methods were effective but specific methods appeared to be more effective. They suggested that this might result from the already well-developed strength and power base in highly-trained athletes, which was not further improved by additional non-specific training methods.

EFFECTS OF SPRINT RUNNING ON SPRINTING SPEED IN HIGHLY TRAINED ATHLETES

Study selection

Population – highly-trained, adult athletes only

Intervention – sprint running training only

Comparison – baseline or non-training control

Outcome – sprint running performance over a distance of <100m

Results

The following studies were identified that fit the selection criteria: Majdell (1991), Spinks (2007), Mujika (2009), Clark (2010), Upton (2011), Alcaraz (2012), West (2013), Lutberget (2015). Almost all of the studies reported that standard sprint running training improved the performance of the athletes in tests of sprint running over short distances. It seems likely that a lack of improvement in a small minority of the studies was observed because of the highly-trained nature of the subjects, making it difficult to generate and identify further enhancements in speed.

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EFFECTS OF SPRINT RUNNING ON SPRINTING SPEED IN RECREATIONAL ATHLETES

Study selection

Population – recreationally-trained, adult athletes only

Intervention – sprint running training only

Comparison – baseline or non-training control

Outcome – sprint running performance over a distance of <100m

Results

The following studies were identified that fit the selection criteria: Callister (1988), Dawson (1998), Rimmer (2000), Zafeiridis (2005), Lockie (2012). Almost all of the studies reported that standard sprint running training improved the performance of the recreationally-trained individuals in tests of sprint running over short distances. Why there was a lack of improvement in a small minority of the studies is unclear.

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CONCLUSIONS REGARDING SPRINTING

Sprint running training is effective for improving sprint running performance in both recreational and highly-trained athletes, as might be expected based on the principle of specificity. Highly-trained athletes might benefit more from sprint running training than less specific methods, while recreationally-trained athletes may benefit similarly from both specific and non-specific approaches.

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RESISTED SPRINTING TRAINING FOR SPRINTING

PURPOSE

This section sets out the extent to which resisted sprinting (using either elastic bands or towing a sled) is effective for improving sprinting speed in either recreationally-trained or highly-trained adult athletes.

BACKGROUND

Introduction

Resisted sprinting training is a relatively new method of training for improving sprinting speed involving sprinting with additional resistance. The resistance can be either vertically directed (using a weighted vest) or horizontally directed (using either elastic bands or towing a weighted sled). The most commonly-investigated form of resisted sprint training is the sled, which has been explored in most acute and chronic trials, although other forms of resistance have been assessed, such as parachutes (Alcarez et al. 2008), pulley systems (Kristensen et al. 2006), elastic bands (Myer et al. 2007), and weighted belts or vests (Alcarez et al. 2008, Cronin et al. 2008). Researchers performing reviews of resisted sprinting have previously concluded that resisted sprinting is effective for increasing sprinting speed but no more effective than conventional sprinting training (Hrysomallis, 2012).

Effects of resisted sprinting on kinematics

Introduction

Some coaches have suggested that resisted sprint running (especially using heavier loads) would likely not improve sprint running performance because it would adversely affect sprint technique (Lavrienko et al. 1990; Pauletto, 1993; Jakalski, 1998). Consequently, many researchers have investigated whether resisted sprint running does in fact alter movement patterns acutely (Letzelter et al. 1995; Lockie et al. 2003; Corn and Knudson, 2003; Murray et al. 2005; Alcaraz et al. 2008; Cronin et al. 2008).

Effects on stride length and stride frequency

In general, it seems that resisted sprint running with almost any load causes a reduction in stride length, and potentially also a reduction in stride frequency. In general, it seems that such reductions increase with increasing level of resistance (usually increasing sled load). In an early investigation, Letzelter et al. (1995) tested the effects of sled towing in trained female sprinters with a range of loads. All loads caused a reduction in stride length and stride frequency, and the reductions increased with increasing load. Later, Lockie et al. (2003) tested the effects of 12.6% and 32.2% of bodyweight in male field sports athletes. They found similar results to Letzelter et al. (1995). All loads caused a reduction in stride length and stride frequency, although only stride length reduced more with increasing load. Corn and Knudson (2003), Murray et al. (2005) and Maulder et al. (2008) all found that resisted sprint running (with a range of loads and modalities) led to reductions in stride length but not stride frequency. Similarly, Cronin et al. (2008) found that both stride length and stride frequency were reduced by resisted sprint running, but that the reduction in stride length was much more substantial than the reduction in stride frequency. Alcarez et al. (2008) found reductions in both stride length and stride frequency.

Effects on other parameters

Resisted sprint running appears to alter a range of other aspects of sprint running movement patterns and these alterations seem to be generally more marked with heavier loads. Common changes in movement patterns are an increase in ground contact time, and an increase in forward trunk lean. Letzelter et al. (1995) tested the effects of sled towing on movements patterns in trained female sprinters with loads of 2.5, 5.0, and 10.0kg. Only the heaviest load caused a substantial increase in ground contact time, a substantial increase in forward trunk lean, and an alteration in hip joint angle at ground contact. Later, Lockie et al. (2003) tested the effects of 12.6% and 32.2% of bodyweight in male field sports athletes. In this case, both loads caused an increase in ground contact time and a substantial increase in forward trunk lean, but only ground contact time lengthened more with increasing load. Cronin et al. (2008) also observed increases in ground contact time and forward trunk lean during resisted sprint running and Alcarez et al. (2008) similarly found an increase in forward trunk lean. In contrast, Maulder et al. (2008) investigated but did not observe any change in ground contact time as a result of using resisted sprint running, even though a range of loads was used in sled towing up to 20% of bodyweight.

Effect of resisted sprint running on kinetics

The acute effects of resisted sprint running on kinetics have been investigated in a small number of acute studies, which have all taken very different approaches to the problem (Martinez-Valencia et al. 2013; Okkonen and Häkkinen, 2013; Andre et al. 2013; Cottle et al. 2014; Kawamori et al. 2014). Okkonen and Häkkinen (2013) compared the kinetics, of block sprint starts with those of sled-pulling and selected squat type exercises. They found that sled-pulling and countermovement jumps displayed the most velocity- and movement-specificity to the block sprint start. Cottle et al. (2014) compared propulsive ground reaction forces between sled-pulling with different loads and the staggered sprint start. They found that only a load of 20% bodyweight was large enough to have a meaningful training effect for the sprint start, when measured by propulsive ground reaction forces. Kawamori et al. (2014) compared horizontal ground reaction forces during short (5m) sprints unweighted and with sled loads of 10% and 30% of bodyweight. Only the heaviest load was sufficient to increase horizontal ground reaction forces during short sprints. These findings indicate that sled towing is likely a specific exercise for short sprints and block sprint starts and may be effective for helping athletes develop the ability to produce the horizontal force that is thought to be important for sprint running, particularly during periods of acceleration.

Mechanisms of action

Sprint running has been widely recognised as a highly effective training method for improving sprinting speed by athletes and coaches, most probably since the dawn of the Olympic games. As noted above, is likely that sprint running training improves sprinting speed by a number of different mechanisms, but most likely increases in velocity-specific force production and superior motor coordination in the sprint running movement. Resistance training has been commonly included in training programs for enhancing sprinting speed only for the last few decades. Resistance training is most likely effective because of its ability to improve force production at slower velocities, which then enhances the ability to produce force at higher velocities by virtue of the force-velocity relationship inherent in muscles. Surprisingly, the combination of both sprinting and resistance training has only been introduced into athletic development programs in the last few years. However, it is essentially only a more specific form of resistance training and is very likely effective simply through its ability to improve force production.

META-ANALYSES

Recreationally-trained athletes

Few meta-analyses or systematic reviews have analysed the benefits of resisted sprint running training on sprint running performance, likely because it is a relatively new training method and there is little literature in this area in comparison with more traditional training methods, such as resistance training. Rumpf et al. (2014) performed meta-analyses regarding the effects of various types of training modality for improving sprint running performance in recreational athletes. Firstly, they grouped training methods into specific (sprinting or resisted sprinting) and non-specific (plyometrics, resistance training, and ballistic training). They noted that both specific and non-specific training methods were similarly effective in recreational athletes for improving sprint running speeds. This indicates that resisted sprint running training is likely effective for improving sprint running performance in recreationally-trained athletes. However, this meta-analysis was limited as not all of the identified studies presented data in a format suitable for combining into an overall effect size. Different results might have been observed if these studies had disclosed this information. Also, many of the studies included that were classified as being performed in “recreational athletes” were performed in physical education students and it was not clear from the details included in the individual studies that they were all also competitive athletes at some level. This meta-analyses in this part of the investigation by Rumpf et al. (2014) may therefore include some groups that were relatively untrained.

Highly-trained athletes

As noted above, resisted sprinting can improve sprint running ability in recreationally-trained athletes. The picture is similar in highly-trained athletes, although this group may benefit to a greater extent. Rumpf et al. (2014) performed meta-analyses regarding the effects of various types of training on sprint running performance in highly-trained athletes. Firstly, they grouped training methods into specific (sprinting or resisted sprinting) and non-specific (plyometrics, resistance training, and ballistic training). They found that both specific and non-specific training methods were effective but specific methods appeared to be more effective. They suggested that this might result from the already well-developed strength and power base in highly-trained athletes, which was not further improved by additional non-specific training methods.

EFFECTS OF RESISTED SPRINTING ON SPRINTING SPEED IN HIGHLY TRAINED ATHLETES

Study selection

Population – highly-trained, adult athletes only

Intervention – resisted sprint running training

Comparison – baseline, normal training control, or non-training control

Outcome – sprint running performance over a distance of <100m

Results

The following studies were identified that fit the selection criteria: Spinks (2007), Harrison (2009), Clark (2010), Upton (2011), Alcaraz (2012), West (2013), Lutberget (2015). Almost all of the studies reported that resisted sprint running training improved the performance of the highly-trained individuals in tests of sprint running over short distances. Why there was a lack of improvement in a small minority of the studies is unclear.

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EFFECTS OF RESISTED SPRINTING ON SPRINTING SPEED IN RECREATIONALLY TRAINED SUBJECTS

Study selection

Population – recreationally-trained, adult athletes only

Intervention – resisted sprint running training

Comparison – baseline, normal training control, or non-training control

Outcome – sprint running performance over a distance of <100m

Results

The following studies were identified that fit the selection criteria: Zafeiridis (2005), Kristensen (2006), Myer (2007), Lockie (2012), Kawamori (2013), Bachero-Mena (2014). Almost all of the studies reported that resisted sprint running training improved the performance of the recreationally-trained individuals in tests of sprint running over short distances. Why there was a lack of improvement in a small minority of the studies is unclear.

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EFFECTS OF LOAD DURING RESISTED SPRINTING ON SPRINTING SPEED

Study selection

Population – either recreationally-trained or highly-trained, adult athletes

Intervention – resisted sprint running training with >2 different loads

Comparison – baseline, normal training control, non-training control, and resisted sprint running training with different load

Outcome – sprint running performance over a distance of <100m

Results

The following studies were identified that fit the selection criteria: Kawamori et al. (2013), Bachero-Mena et al. (2014). Both studies found that sled towing with different loads improved sprint running ability similarly. There was no indication that using heavier loads was detrimental to sprint running performance. This is in contrast to the popular belief that heavy sled towing loads cannot improve sprint running ability as they alter movement patterns.

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CONCLUSIONS REGARDING SPRINTING

Resisted sprint running training using a range of modalities (sled, elastic cord, chutes, weighted vests) and both light and heavy loads appears to be effective for improving sprint running performance in athletes. Highly-trained athletes might benefit more from resisted sprint training than less specific methods, while recreationally-trained athletes may benefit similarly from specific and non-specific approaches.

Acutely, resisted sprint running involves substantially smaller stride lengths (and slightly lower stride frequency) than unresisted sprint running. It also involves longer ground contact times and greater forward trunk lean. Heavier loads appear to alter movement patterns more than light loads but this does not appear to affect long-term outcomes.

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RESISTANCE TRAINING FOR SPRINTING

PURPOSE

This section sets out the extent to which conventional resistance training is effective for improving sprinting speed in either recreationally-trained or highly-trained adult athletes.

BACKGROUND

Introduction

Resistance training is a fairly traditional method for enhancing sports performance. It increases muscular strength and size and thereby improves the ability of the athlete to produce force. Before the widespread introduction of resistance training, many coaches believed that lifting weights would be ineffective (as the exercises were not sports-specific) and would slow athletes down by making them bulky, heavy and “musclebound” but this criticism was later found to be unjustified. Interestingly, it is possible to draw many parallels between the arguments directed by the opponents of resistance training 30 – 40 years ago and the arguments cited by coaches who oppose the use of heavy resisted sprint training today. As with resisted sprint training, during resistance training, the actual load can be either vertically directed (using axial exercises such as squats or deadlifts) or horizontally directed (using antero-posterior exercises such as pull-throughs, hip thrusts, glute bridges, or horizontal back extensions).

Mechanisms of action

Resistance training has been commonly included in training programs for enhancing sprinting speed only for the last few decades. Resistance training is most likely effective because of its ability to improve force production at slower velocities, which then enhances the ability to produce force at higher velocities by virtue of the force-velocity relationship inherent in muscles.

META-ANALYSES

Recreationally-trained athletes

Resistance training has been extensively explored for improving sprint running speed and consequently, meta-analysis of a range of studies is possible. Rumpf et al. (2014) performed meta-analyses regarding the effects of various types of training modality for improving sprint running performance in recreational athletes. Firstly, they grouped training methods into specific (sprinting or resisted sprinting) and non-specific (plyometrics, resistance training, and ballistic training). They noted that both specific methods and non-specific methods (like resistance training) were similarly effective in recreational athletes for improving sprint running speeds. Indeed, several investigators have confirmed that resistance training in general and the squat exercise in particular are effective for enhancing sprint running ability. Cronin et al. (2007) reviewed the literature and reported that increases in maximal squat strength following from long-term programs of resistance training were associated with reductions in sprint times. However, they also noted that substantial increases in squat strength were required in recreationally trained athletes for a meaningful reduction in sprint running. Specifically, they observed that around 23% increases in maximal squat strength were needed to achieve reductions in sprint times of around 2%. More recently, Seitz et al. (2014) explored the longitudinal relationship between increases in lower body strength (as measured by 1RM back squat) and increases in sprint running performance over distances <40m. They reported a statistically significant correlation between squat effect size and sprint effect size, with a relatively large relationship (R-squared = 0.60). This supports previous cross-sectional findings that have found close associations between 1RM back squat and short-distance sprint running ability (e.g. Wisløff et al. 2004). It is therefore relatively clear that resistance training in general and the back squat exercise in particular can improve sprint running performance. However, both of these investigations were limited as they included a range of subjects, including those with very limited athletic training experience. Whether such a strong relationship would exist if the less well-trained individuals were eliminated from the above analyses is unclear.

Highly-trained athletes

As noted above, meta-analyses have reported that resistance training can improve sprint running ability and that increases in maximal squat strength are associated with reductions in sprint times in recreational athletes, albeit including those of relatively low training experience. Such findings are likely to apply to highly-trained athletes as well, at least to a certain degree. Indeed, Wisloff et al. (2004) have reported strong cross-sectional correlations between maximal squat strength and short distance sprint running performance in international male soccer players. Rumpf et al. (2014) performed meta-analyses regarding the effects of various types of training on sprint running performance in highly-trained athletes. Firstly, they grouped training methods into specific (sprinting or resisted sprinting) and non-specific (plyometrics, resistance training, and ballistic training). They found that both specific and non-specific training methods were effective. However, they noted that non-specific methods, such as resistance training, were much less effective for highly-trained athletes. They suggested that this might result from their already well-developed strength and power base, which was not further improved by additional resistance training. In conjunction with the fact that highly-trained athletes are unlikely to be able to develop maximal squat (or other exercise) strength by a substantial amount, this may indicate that highly-trained athletes should spend less time using non-specific methods and more time using specific methods.

EFFECTS OF RESISTANCE TRAINING ON SPRINTING SPEED IN ATHLETES

Study selection

Population – either recreationally-trained or highly-trained, adult athletes

Intervention – resistance training

Comparison – baseline, normal training control, or non-training control

Outcome – sprint running performance over a distance of <100m

Results

The following studies were identified that fit the selection criteria: Fry (1991), Hoffman (1991), Wilson (1993), Wilson (1996), Murphy (1997), Harris (2000), Blazevich (2002), Askling (2003), Hoffman (2004), Kotzamanidis (2005), Dodd (2007), Rønnestad (2008), Mujika (2009), Chelly (2009), Helgerud (2011), Hermassi (2011), Rønnestad (2011), Lockie (2012), Comfort (2012), Sander (2013), Loturco (2013), Koundourakis (2014), Brito (2014), Thomas (2014). The large majority of these studies found that resistance training improved sprint running performance in athletes. Many of the included studies used the back squat, although there were some examples where the back squat was not used and yet improvements were still observed (e.g. Askling et al. 2003).

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EFFECTS OF LOAD DURING RESISTANCE TRAINING ON SPRINTING SPEED

Study selection

Population – either recreationally-trained or highly-trained, adult athletes

Intervention – resistance training with >2 different loads (and therefore bar speeds)

Comparison – baseline, normal training control, non-training control, and resistance training with different load

Outcome – sprint running performance over a distance of <100m

Results

The following studies were identified that fit the selection criteria: Harris (2000), Blazevich (2002). Both studies found no differences between programs of slow and fast resistance training. This suggests that using lighter loads and faster bar speeds may not be critical for maximizing sprint running adaptations from resistance training in trained athletes.

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EFFECTS OF EXERCISE DURING RESISTANCE TRAINING ON SPRINTING SPEED

Study selection

Population – either recreationally-trained or highly-trained, adult athletes

Intervention – resistance training with >2 different exercises

Comparison – baseline, normal training control, non-training control, and resistance training with different load

Outcome – sprint running performance over a distance of <100m

Results

The following studies were identified that fit the selection criteria: Speirs (2015). This study found no differences in the improvement in sprint running ability in team sports athletes between programs of bilateral back squat and rear-foot elevated split squat training. This suggests that the exact type of exercise used to develop the lower body musculature may not be critical for maximizing sprint running adaptations from resistance training in trained athletes.

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CONCLUSIONS REGARDING SPRINTING

Resistance training using a range of exercises appears to be effective for improving sprint running performance in athletes. Using lighter loads and faster bar speeds does not appear to produce better results than heavy loads and slow bar speeds. The effect of exercise selection is currently unclear.

Highly-trained athletes might benefit less from non-specific methods like resistance training, while recreationally-trained athletes may benefit similarly from both specific and non-specific approaches.

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PLYOMETRICS TRAINING FOR SPRINTING

PURPOSE

This section sets out the extent to which plyometrics are effective for improving sprinting speed in either recreationally-trained or highly-trained adult athletes.

BACKGROUND

Introduction

In the context of sprint running, plyometrics are explosive, compound, lower-body movements involving the stretch-shortening cycle (see review by Markovic and Mikulic, 2010). They are generally always performed without load or with very low loads, which is what distinguishes them from ballistic resistance training. As is well-known, the term “plyometrics” was first popularised by the Soviet jumping coach, Verkoshansky. Verkoshansky wanted to explore ways to develop the jumping ability of athletes who had already attained significant gains using standard methods at the time, which comprised jumping practice and resistance-training. Verkoshansky reasoned that since there seemed to be a correlation between short ground contact times and better performances in triple jumpers, this could imply that a greater stiffness (or a superior ability to store and release elastic energy) could be the key to improved jumping ability. Thus, he started using depth jumps with his athletes in order to increase their ability to switch from eccentric muscle actions to concentric muscle actions more quickly, thereby reducing ground contact times (see review by Faccioni, 2001). While some coaches still think of plyometrics in these terms, the usage in the modern literature has changed substantially and its meaning is somewhat broader.

Mechanisms of action

Introduction

Since sprint running involves both eccentric and concentric muscle actions, the ability to generate maximal force during running is also dependent upon the behavior of the stretch-shortening cycle and the stiffness of the lower body. It is often stated that such plyometrics are the key to bridging the qualities of strength and power or other related high-velocity expressions of strength (see for example the review by McNeely, 2005), although exactly how this might be mediated is unclear. It is might be mediated as Verkoshansky suspected, by alterations in stiffness. Alternatively, other physiological adaptations might occur that cause an improved ability to store and release elastic energy during high-velocity eccentric and concentric muscle actions.

Effect of velocity and acceleration

The velocity of the sprint and whether or not the athlete is accelerating may affect the degree to which elastic energy storage and/or stiffness are important for sprint running performance. In respect of velocity, Cavagna (2006) found that the increase in stretching velocity of the hip extensors and knee flexors in the terminal swing phase of sprint running increases with increasing speed. This implies that the elastic elements of the muscle-tendon units contribute more to force production at faster running speeds. Thus, it might be expected that training methods that help improve elastic energy storage might help improve sprint running performance to a greater degree at faster speeds than at slower speeds. Additionally, Roberts (2002) found that several studies in animal models reported that muscles during constant speed running change length only slightly but contract more or less isometrically, while the tendon in series undergoes large changes in length. This is in contrast to acceleration running, whereby the muscles shorten considerably while undergoing concentric contractions. This implies that the elastic elements of the muscle-tendon units contribute more to force production at constant-speed sprint running than during accelerating sprint running. Thus, it might be expected that training methods that help improve elastic energy storage might help improve sprint running performance to a greater degree during maximum speed sprint running than during accelerating sprint running.

Beneficial effects of drop jumps

Given that our current understanding of the mechanisms by which plyometrics are effective suggests that they might be most effective for maximum speed sprint running, it is interesting that some studies have reported that drop jump height is the most effective way to predict maximum sprinting speed out of a range of vertical and horizontal jumping tests (Bissas and Havenetidis, 2008; Kale et al. 2009; McCurdy et al. 2010). Drop jumps are believed to be the most effective way of enhancing elastic energy storage and improving reactive strength by increasing stiffness. For the sake of balance, it is important to note that some other studies have found drop jump performance to be not strongly correlated with sprint running performance (e.g. Salaj and Markovic, 2011). It is also noteworthy that some studies have found that horizontal jumps are highly correlated with sprint running performance (e.g. Holm et al. 2008; Hudgins et al. 2012) and may be better predictors of sprint running ability than vertical jumps (e.g. Maulder and Cronin, 2005; Meylan et al. 2009; Habibi et al. 2010; Robbins, 2012; Robbins and Young, 2012). Overall, it seems likely that drop jumps are an effective training tool for increasing maximum sprinting speed by increasing the amount of energy stored in the eccentric phase of ground contact.

META-ANALYSES

Recreationally-trained athletes

Introduction

Plyometrics have been extensively explored for improving sprint running speed and consequently, meta-analysis of a range of studies is possible. Rumpf et al. (2014) performed meta-analyses regarding the effects of various types of training modality for improving sprint running performance in recreational athletes. Firstly, they grouped training methods into specific (sprinting or resisted sprinting) and non-specific (plyometrics, resistance training, and ballistic training). They found that both specific and non-specific training methods were similarly effective in this population. Moreover, they found that plyometrics were the most effective out of all non-specific methods (which also included resistance training and ballistic training). Additionally, Sáez de Villarreal et al. (2012b) performed a meta-analysis assessing the effect of plyometric training but this investigation was performed in both untrained and trained individuals and did not report sub-group analysis for trained subjects or athletes. Also, the extent to which training experience contributed to the heterogeneity of the results was not formally explored by the investigators. It is therefore necessary to be cautious about drawing strong conclusions from these findings for athletes. Nevertheless, in this meta-analysis, Sáez de Villarreal et al. (2012b) reported several interesting findings that may be relevant to recreationally-trained athletes, as set out below.

Effect of plyometrics

Firstly, Sáez de Villarreal et al. (2012b) concluded that plyometrics do improve sprint running performance across both trained and untrained individuals. Although there was no sub-group analysis performed and no analysis of the heterogeneity resulting from the level of experience of the included subjects, the effect in recreationally-trained athletes can be confirmed from a straightforward review of the available literature and from other more well-defined meta-analyses in more specific athletic populations (e.g. Rumpf et al. 2014). The comparison between plyometrics and other modalities is discussed below.

Dose-response of plyometrics

Secondly, Sáez de Villarreal et al. (2012b) concluded that the use of plyometrics for improving sprinting ability is a dose-responsive effect across both trained and untrained individuals, and they proposed that correct dose has a significantly better effect than too much or too little. They suggested an optimal dose of around 3 sessions per fortnight, with >80 jumps per session. These findings are somewhat supported by a direct trial, albeit one that was also performed in untrained subjects only (Sáez de Villarreal et al. 2008), where 2 sessions per week of 60 jumps per session was found to be the optimal volume. Although these findings appear robust across a range of populations, the exact dose-response in recreationally-trained athletes is unclear.

Exercise selection during plyometrics

Thirdly, Sáez de Villarreal et al. (2012b) concluded that the choice of exercise is important during plyometrics across trained and untrained individuals. Specifically, they found that using either a range of different plyometrics or even simply both a squat jump and a drop jump in combination produced greater effects than either a squat jump or drop alone in isolation. The exact reasons for this are unclear but may relate to the different qualities being trained by each type of exercise. Moreover, whether the same effect would be observed in recreationally-trained athletes is unknown.

Highly-trained athletes

As noted above, meta-analyses have reported that plyometrics can clearly improve sprint running ability in recreationally-trained athletes. The picture regarding highly-trained athletes is less clear. Rumpf et al. (2014) performed meta-analyses regarding the effects of various types of training on sprint running performance in highly-trained athletes. Firstly, they grouped training methods into specific (sprinting or resisted sprinting) and non-specific (plyometrics, resistance training, and ballistic training). They found that both specific and non-specific training methods were effective. However, they noted that non-specific methods, such as plyometrics, were much less effective for highly-trained athletes than for recreationally-trained athletes and that more specific methods (such as sprinting or resisted sprinting) were better. They suggested that this might result from the already well-developed strength and power base in highly-trained athletes, which was not further improved by additional plyometrics.

EFFECTS OF PLYOMETRICS ON SPRINTING SPEED IN ATHLETES

Study selection

Population – either recreationally-trained or highly-trained, adult athletes

Intervention – plyometrics

Comparison – baseline, normal training control, or non-training control

Outcome – sprint running performance over a distance of <100m

Results

The following studies were identified that fit the selection criteria: Wilson (1993), Wagner (1997), Rimmer (2000), Chimera (2004), Moore (2005), Reyment (2006), Dodd (2007), Impellizzeri (2008), Thomas (2009), Chelly (2010), Sedano (2011), Arazi (2011), Nakamura (2012), Lockie (2012), Chelly (2014), Brito (2014). The large majority of these studies found that plyometrics improved sprint running performance in athletes. The type of plyometrics used ranged from traditional depth jumps to hurdle jumps and standard countermovement jumps.

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EFFECTS OF EXERCISE DURING PLYOMETRICS ON SPRINTING SPEED IN ATHLETES

Study selection

Population – either recreationally-trained or highly-trained, adult athletes

Intervention – plyometrics with >2 different exercises

Comparison – baseline, normal training control, non-training control, and resistance training with different load

Outcome – sprint running performance over a distance of <100m

Results

The following studies were identified that fit the selection criteria: Impellizzeri (2008), Thomas (2009), Arazi (2011). Impellizzeri et al. (2008) compared grass-based or sand-based plyometrics and found that both improved sprint running ability to a similar extent. Arazi et al. (2011) compared water-based and land-based plyometrics (ankle jumps, speed marching, squat jumps, and skipping drills) and also found that both improved sprint running ability to a similar extent. Thomas et al. (2009) compared traditional depth jumps with standard countermovement jumps and found that neither improved sprint running ability. It is therefore difficult to assess which type of plyometric exercise might be best for enhancing sprint running ability based on long-term trials.

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CONCLUSIONS REGARDING SPRINTING

Plyometrics using a range of exercises appears to be very effective for improving sprint running performance in athletes. However, highly-trained athletes might benefit less from non-specific methods like plyometrics, while recreationally-trained athletes may benefit similarly from specific and non-specific approaches.

It is currently hard to assess which plyometrics exercises are best for improving sprint running speed, although a variety of jumps appears to be better than using only a single type of jump.

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BALLISTIC TRAINING FOR SPRINTING

PURPOSE

This section sets out the extent to which ballistic training is effective for improving sprinting speed in either recreationally-trained or highly-trained adult athletes.

BACKGROUND

Introduction

Ballistic training is a form of resistance training in which there is no deceleration phase. In practice, this means releasing the external load into the air. The lack of a deceleration phase means that athletes are able to increase the duration of time spent accelerating when performing this type of training. This longer period of time spent acceleration is thought to enhance the adaptations to training. The most commonly-used ballistic training exercise for the lower body during sprint running training programs is the jump squat, although many Olympic weightlifting exercises and their variations (such as power cleans) are also in common usage. Some researchers and strength and conditioning coaches use the term ballistic training to refer to light-load resistance training exercise performed explosively but with a deceleration phase. However, from a biomechanical perspective, this is not a correct use of terminology. This confusion may be quite important, as light-load resistance training exercise performed explosively with a deceleration phase does not allow athletes to continue accelerating for as long as genuinely ballistic exercises.

META-ANALYSES

Recreationally-trained athletes

Few meta-analyses or systematic reviews have analysed the benefits of ballistic training on sprint running performance. Rumpf et al. (2014) performed meta-analyses regarding the effects of various types of training modality for improving sprint running performance in recreational athletes. Firstly, they grouped training methods into specific (sprinting or resisted sprinting) and non-specific (plyometrics, resistance training, and ballistic training). They noted that both specific and non-specific training methods were similarly effective in recreational athletes for improving sprint running speeds. This indicates that ballistic training is likely effective for improving sprint running performance in recreationally-trained athletes. However, this meta-analysis was limited as not all of the identified studies presented data in a format suitable for combining into an overall effect size. Different results might have been observed if these studies had disclosed this information. Nevertheless, these findings are support by Sáez de Villarreal et al. (2012b), who performed a meta-analysis assessing the effect of plyometric training on sprinting performance. In this investigation, they analysed plyometric exercises with and without additional loading, which is essentially the definition of ballistic resistance training. They reported that the addition of weight to an exercise (i.e. a loaded countermovement jump) was similarly effective at improving sprinting performance as the unweighted equivalent (i.e. a standard countermovement jump). Although this meta-analysis was limited as it was performed across both trained and untrained subjects, this supports the use of ballistic training for recreationally-trained athletes to develop sprinting ability.

Highly-trained athletes

As noted above, ballistic training appears to be able to improve sprint running ability in recreationally-trained athletes. The picture is similar in highly-trained athletes, although this group may not benefit to the same extent. Rumpf et al. (2014) performed meta-analyses regarding the effects of various types of training on sprint running performance in highly-trained athletes. Firstly, they grouped training methods into specific (sprinting or resisted sprinting) and non-specific (plyometrics, resistance training, and ballistic training). They found that both specific and non-specific training methods were effective but the non-specific methods appeared to be much less effective. They suggested that this might result from the already well-developed strength and power base in highly-trained athletes, which was not further improved by additional non-specific training methods, such as ballistic training.

EFFECTS OF BALLISTIC TRAINING ON SPRINTING SPEED IN ATHLETES

Study selection

Population – either recreationally-trained or highly-trained, adult athletes

Intervention – ballistic resistance training, including Olympic weightlifting or its variations

Comparison – baseline, normal training control, or non-training control

Outcome – sprint running performance over a distance of <100m

Results

The following studies were identified that fit the selection criteria: Wilson (1993), McEvoy (1998), McBride (2002), Hoffman (2004), Hoffman (2005), Moore (2005), Harris (2008), Balsalobre-Fernández (2013). The majority of these studies reported that ballistic training was effective for improving sprint running speeds, although a large minority failed to observe any improvement. It therefore seems likely that ballistic training can improve sprint running ability in athletes.

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EFFECT OF LOAD DURING BALLISTIC TRAINING ON SPRINTING SPEED IN ATHLETES

Study selection

Population – either recreationally-trained or highly-trained, adult athletes

Intervention – >2 ballistic resistance training programs using different loads, including Olympic weightlifting or its variations

Comparison – baseline, normal training control, or non-training control, another ballistic resistance training program using a different load

Outcome – sprint running performance over a distance of <100m

Results

The following studies were identified that fit the selection criteria: McBride (2002), Harris (2008). Most of the measures reported by these studies indicated that there was no difference in relation to the load used on changes in sprint running ability. There was one outcome in which a lighter load led to a superior improvement than a heavier load, which may suggest that lighter loads and faster movement speeds are beneficial during ballistic training for enhancing sprint running speeds but this is uncertain.

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CONCLUSIONS REGARDING SPRINTING

Ballistic training is effective for improving sprint running ability in athletes. The exact exercise or load to use during ballistic training is currently unclear, although a lighter load may possibly be more beneficial than a heavier load.

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COMBINED TRAINING METHODS FOR SPRINTING

PURPOSE

This section sets out the extent to combined training programs can be effective for improving sprinting speed in either recreationally-trained or highly-trained adult athletes.

META-ANALYSES

Recreationally-trained athletes

Few meta-analyses or systematic reviews have analysed the benefits of combined training methods on sprint running performance. Rumpf et al. (2014) performed meta-analyses regarding the effects of various types of training modality for improving sprint running performance in recreational athletes. Firstly, they grouped training methods into specific (sprinting or resisted sprinting), non-specific (plyometrics, resistance training, and ballistic training), and combined approaches. They noted that both specific and non-specific training methods were similarly effective in recreational athletes for improving sprint running speeds but that a combined approach was much less effective than either of these methods. This indicates that combined training for improving sprint running performance in recreationally-trained athletes is not advisable. However, this meta-analysis was limited as not all of the identified studies presented data in a format suitable for combining into an overall effect size. Different results might have been observed if these studies had disclosed this information. Also, many of the studies included that were classified as being performed in “recreational athletes” were performed in physical education students and it was not clear from the details included in the individual studies that they were all also competitive athletes at some level. This meta-analyses in this part of the investigation by Rumpf et al. (2014) may therefore include some groups that were relatively untrained.

Highly-trained athletes

As noted above, combined training appears to be less effective for improving sprint running ability in recreationally-trained athletes than either specific or non-specific methods used in isolation. The picture is very different in highly-trained athletes. Rumpf et al. (2014) performed meta-analyses regarding the effects of various types of training on sprint running performance in highly-trained athletes. Firstly, they grouped training methods into specific (sprinting or resisted sprinting), non-specific (plyometrics, resistance training, and ballistic training) and combined approaches. They found that both specific and combined training methods were similarly effective while the non-specific methods were much less effective. They suggested that this might result from the already well-developed strength and power base in highly-trained athletes, which was not further improved by additional non-specific training methods. They suggested that the success of the combined methods may have arisen through the greater overload that occurred with challenging different neuromuscular qualities simultaneously.

COMBINED TRAINING METHODS FOR ENHANCING SPRINTING SPEED IN ATHLETES

Study selection

Population – either recreationally-trained or highly-trained, adult athletes

Intervention – combined training programs, including >2 of any of the following: sprint running, resisted sprint running, resistance training, ballistic resistance training (including Olympic weightlifting), or plyometrics

Comparison – baseline, normal training control, or non-training control

Outcome – sprint running performance over a distance of <100m

Results

The following studies were identified that fit the selection criteria: Majdell (1991), Lyttle (1996), Gorostiga (2004), Kotzamanidis (2005), Hoffman (2005), Marques (2006), Spinks (2007), Rønnestad (2008), Tsimahidis (2010), Faude (2013), Los Arcos (2014). The majority of these studies reported that combined training was effective for improving sprint running speeds, although a large minority failed to observe any improvement. It therefore seems likely that combined training can improve sprint running ability in athletes.

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CONCLUSIONS REGARDING SPRINTING

Combined training appears to be effective for improving sprint running performance in athletes. However, recreationally-trained athletes might benefit much less from combined methods than highly-trained athletes.

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COMPARISONS OF TRAINING METHODS FOR SPRINTING

PURPOSE

This section sets out the extent to which different training methods are more or less effective for improving sprinting speed in either recreationally-trained or highly-trained adult athletes.

COMPARISON OF TRAINING METHODS FOR ENHANCING SPRINTING SPEED IN ATHLETES

Study selection

Population – either recreationally-trained or highly-trained, adult athletes

Intervention – either sprint running, resisted sprint running, resistance training, ballistic resistance training (including Olympic weightlifting), or plyometrics

Comparison – baseline, normal training control, or non-training control

Outcome – sprint running performance over a distance of <100m

Results

The following studies were identified that fit the selection criteria: Wilson (1993), Rimmer (2000), Hoffman (2004), Kotzamanidis (2005), Moore (2005), Dodd (2007), Lockie (2012), Brito (2014). Almost all of the studies uniformly reported that there was no difference between any of the training modalities tested, which suggests that any of the above approaches are valuable and appropriate for improving sprinting speed. Lockie et al. (2012) found that resistance training was superior to sprinting, resisted sprinting and plyometrics in recreationally-trained athletes and Kotzamanidis et al. (2005) reported that a combined program of both resistance training and sprinting was superior to a program of resistance training alone. The inherent ability of the athlete therefore seems to have a far bigger role to play in their response to training than the training method selected.

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CONCLUSIONS REGARDING SPRINTING

Many training methods can increase sprinting speed in athletes, including conventional sprinting training, resisted sprinting, resistance training, ballistic training, and plyometrics. Comparisons of these training methods have not yet identified which is best.

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BIOMECHANICS OF SPRINTING

INTRODUCTION

When determining a training program for improving sprint running, the evidence-based sports or strength coach will always begin with the evidence from long-term trials (English et al. 2012). Consequently, where a substantial body of long-term trials shows that a training method is effective or ineffective, this can be taken as the best possible quality of information for building a training program. However, as can be seen from the preceding sections, there are many different training methods that are effective for sprint running and it is unclear which are best and how each can be implemented for maximum effect. Assessment of the biomechanics of sprint running can provide clues (but by no means certainty) regarding the optimal ways to structure the different training methods for maximal effect.

BIOMECHANICS SECTION CONTENTS

Click on the links below to jump down to the relevant part of the biomechanics section:

Stride length and stride frequency

Ground contact time and flight time

Joint angle movements

Ground reaction forces

Joint moments

Stiffness

Electromyography (EMG)

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STRIDE LENGTH AND FREQUENCY

PURPOSE

This section sets out the research relating to stride length and stride frequency.

BACKGROUND

Introduction

Stride length is the distance covered in a single gait cycle and averages roughly 2.3 – 2.4m in elite track sprinters over a 100m track sprint event. Conversely, stride frequency is the number of strides taken per second, expressed in Hz. Stride frequency averages around 4 – 5Hz in elite track sprinters over a 100m track sprint event. Sprint running velocity is therefore the product of stride length and stride frequency. It is impossible to change sprint running velocity without altering either stride length or stride frequency or both. However, it is perfectly possible to alter either stride length or stride frequency and not change sprint running velocity, so long as an increase in one factor is matched by an equal and opposite reduction in the other. Currently, it is unclear whether one of the two factors (stride length or stride frequency) is more important for determining sprint running performance for everyone, or whether there is simply one combination that is optimal for each individual. Some researchers have proposed that individual variation may be critical and it may be possible to achieve world-class speed through a variety of combinations of stride lengths and stride frequencies.

RELATIONSHIP BETWEEN STRIDE LENGTH AND SPRINTING SPEED

Introduction

There are several ways to analyse the effects of changing stride length with changing running speed. Firstly, stride length can be measured at different constant running speeds performed by a group of individuals. Secondly and similarly, stride length can be measured in several phases of an accelerating sprint in a group of individuals (both of these approaches are called “within individuals”). Correlations can then be drawn to assess the nature of the relationship between stride length and running speed. Such correlations tell us whether running faster involves longer stride lengths. Thirdly, stride length can be measured at maximal sprint running speed between the individuals in a population (called “between individuals”). Correlations can then be drawn to assess the nature of the relationship between stride length and running speed. This tells us whether faster runners display longer stride lengths. Since both approaches are cross-sectional, however, neither really help us assess whether longer stride lengths are a side effect of faster running or whether being able to run using longer stride lengths makes you run faster.

Within individuals

In investigations comparing running speeds within individuals, many researchers have found that when performing an accelerating sprint, stride length increases broadly in line with increasing sprint running velocity (Debaere et al. 2013; Nagahara et al. 2014a; Nagahara et al. 2014b). In addition, researchers have often observed that when measuring stride length in the same group of individuals at different running speeds, stride length increases with increasing running speed (Mero and Komi, 1986; Kyröläinen et al. 1999; Kyröläinen et al. 2001; Brughelli et al. 2011; Dorn et al. 2012).

Between individuals

In investigations comparing running speeds between individuals, some researchers have found that those individuals displaying greater stride length also display faster sprint running velocity (Hunter et al. 2004b; Brughelli et al. 2011; Lockie et al. 2013). However, other researchers have failed to observe this relationship (Morin et al. 2012). It is therefore unclear whether a longer stride length is unequivocally better for sprint running performance.

RELATIONSHIP BETWEEN STRIDE FREQUENCY AND SPRINTING SPEED

Introduction

There are several ways to analyse the effects of changing stride frequency with changing running speed. Firstly, stride frequency can be measured at different constant running speeds performed by a group of individuals. Secondly and similarly, stride frequency can be measured in several phases of an accelerating sprint in a group of individuals (both of these approaches are called “within individuals”). Correlations can then be drawn to assess the nature of the relationship between stride frequency and running speed. Such correlations tell us whether running faster involves higher stride frequencies. Thirdly, stride frequency can be measured at maximal sprint running speed between the individuals in a population (called “between individuals”). Correlations can then be drawn to assess the nature of the relationship between stride frequency and running speed. This tells us whether faster runners display higher stride frequencies. Since both approaches are cross-sectional, however, neither really help us assess whether higher stride frequencies are a side effect of faster running or whether being able to run using higher stride frequencies makes you run faster.

Within individuals

In investigations comparing running speeds during accelerating sprints within individuals, some researchers have found that, stride frequency does not increase substantially with increasing sprint running velocity after the initial 10m has been performed (Nagahara et al. 2014a; Nagahara et al. 2014b). In investigations comparing different trials of constant running speeds within individuals, most researchers have found that stride frequency is substantially greater at faster running speeds than at slower running speeds (Mero and Komi, 1986; Kyröläinen et al. 1999; Kyröläinen et al. 2001; Belli et al. 2001; Kivi et al. 2002; Brughelli et al. 2011; Dorn et al. 2012).

Between individuals

Some researchers have reported that there is a beneficial relationship between stride frequency and sprint running performance between individuals (Mann and Herman, 1985; Morin et al. 2012). Mann and Herman (1985) reported that the difference in first, second and eighth placing during the Olympic 200m was significantly correlated with stride frequency. However, other researchers have not found this relationship (Hunter et al. 2004b; Brughelli et al. 2011; Lockie et al. 2013). Therefore, it is currently unclear whether a faster stride frequency is associated with faster sprint running performance.

INTERACTIONS BETWEEN STRIDE LENGTH AND STRIDE FREQUENCY

Effect of velocity

It has been suggested that velocity might play a key role in determining the intertwined relationships between stride length and stride frequency and sprint running velocity. Nummela et al. (2007) recorded the stride length and stride frequency in 25 endurance athletes over a range of 8 different running speeds from 4m/s to maximum sprinting. They found that speed increases up to 7m/s were achieved by increasing both stride lengths and stride frequencies but above 7m/s, stride frequency was solely responsible. Similarly, in a musculoskeletal modelling study, Dorn et al. (2012) showed that as sprint running speed increases, stride length is the primary mechanism for increasing velocity up to 7m/s and after that a shift occurs and stride frequency becomes the primary mechanism for increasing sprint running velocity.

Effect of individual variation

It seems very probable that individual variation is critical and that it may be possible to achieve world-class speed through a variety of combinations of stride lengths and stride frequencies. Salo et al. (2011) investigated the stride lengths and stride frequencies of the very best 100m sprinters in the world by reviewing the video footage of 52 male elite-level 100m races from publicly available television broadcasts and taking their times from the International Association of Athletics Federations (IAAF) website. It was found that some of the elite track athletes’ performances were more reliant on stride length, while others were more reliant on stride frequency, and some even displayed no significant reliance on either variable. Taylor and Beneke (2012) reported similar findings based on the 3 top-finishing athletes in the 100m World Athletics Championship final of 2009. Although Usain Bolt displayed the greatest velocity over the 60 – 80m split, he had the lowest stride frequency, which was a function of his greater stride length. Also, it was found that stride frequency was very different between the 3 athletes, with Usain Bolt running at 4.49Hz, Tyson Gay at 4.96Hz and Asafa Powell at 4.74Hz. Similar findings were reported by Ito et al. (2008) when they compared the two athletes Tyson Gay and Asafa Powell in the 100m final at the 2007 IAAF World Championships in Athletics in Osaka. These findings suggest that at the elite level there is certainly a wider range of stride lengths and stride frequencies than might be expected if either stride length or stride frequency were the sole, important factor.

TRAINING TO IMPROVE STRIDE LENGTH AND FREQUENCY

Stride length

Some researchers have carried out dedicated investigations to explore which training methods are best for specifically improving stride length. Lockie et al. (2012) found that 6 weeks of either sprint training, resistance training, plyometrics or resisted sprint training all produced significant improvements in stride length in short distance sprint running. Kawamori et al. (2013) compared the effects of an 8-week program of weighted sled towing with either heavy or light loads on sprint running ability, stride length and stride frequency. The sled-towing group using a heavy load involved a reduction in sprint velocity acutely of around 30% and the sled-towing group with a light load involved a reduction in sprint velocity acutely of 10%. Following the training program, the heavy group significantly increased stride length by 8.1% but the light group showed no significant change. Interestingly, neither group improved stride frequency. Finally, although not a long-term trial, Mero and Komi (1994) investigated the acute stride parameters during hopping, stepping and bounding drills. They reported that stride lengths were greatest in the order hopping > stepping > bounding > sprinting, which could imply that such drills are also useful for increasing stride length, although long-term studies are clearly required in this case.

Stride frequency

Some researchers have carried out dedicated investigations to explore which training methods are best for specifically improving stride length. Moir et al. (2007) found that 8 weeks of combined heavy and explosive resistance training improved stride frequency over the first 3 steps of a sprint. Kawamori et al. (2013) explored the effects of an 8-week program of weighted sled towing with either heavy or light loads on stride frequency. Neither the heavy load or light load sled-towing group improved stride frequency. Mero and Komi (1986) investigated overspeed running by towing and found that increases in sprint running velocity occurred as a result of increased stride frequency. Similarly, Ebben (2008) investigated the speed of overspeed sprint running on decline slopes of 2.1, 3.3, 4.7, 5.8 and 6.9 degrees and found that while several slopes produced faster sprint running speeds, a 5.8 degree slope is the optimal slope for overspeed running. Finally, Paradisis and Cook (2001) investigated the factors contributing to increased speed when running on inclined and declined surfaces and found that it was changes in step length that were the primary contributors to changes in speed. For example, on a 3 degree decline, speed increased 9.2% and step length increased 7%. However, following a long-term intervention of decline surface running, the increases in speed following 6 weeks of training indicated that increases in stride frequency were the primary contributing factors (Paradisis and Cook, 2006).

IMPLICATIONS FOR TRAINING

Assuming it is accepted that neither stride length nor stride frequency is the critical factor for all athletes because of inter-individual variation, it follows that every individual has their own ideal combination of stride length and stride frequency. On this basis, Salo et al. (2011) has suggested some athletes may need to rely more on stride length for increased speed and would consequently benefit from high-force training, while other athletes may rely more on stride frequency for increased speed and would consequently benefit from improving leg turnover speed. However, as Hunter et al. (2004b) has stated, “When training an athlete to increase step length or step rate, care must be taken that the increase in one factor is not ‘canceled out’ by a similar or greater decrease in the other factor.” As noted above, it is perfectly possible to alter stride length or stride frequency without improving sprint running velocity, so long as an improvement in one factor is accompanied by a reduction in the other. Moreover, it is unclear at the moment whether it is more beneficial to train an individual according to his strengths or weaknesses. For example, should athletes with superior strength train with a greater proportion of high-force work or with a greater proportion of high-velocity work?

CONCLUSIONS REGARDING SPRINTING

Sprint running velocity is the product of stride length and stride frequency. It is likely possible to achieve world-class speed through a variety of combinations of stride lengths and stride frequencies. The existence of an ideal individual combination of stride length and stride frequency implies that some individuals may need training to improve stride length, while others may need training to improve stride frequency.

Long-term trials indicate that sprint running training, resistance training, plyometrics and resisted sprint training can all increase stride length. Weighted sled towing for improving stride length appears to be most effective with heavier loads. Acute trials suggest that hopping, stepping or bounding drills may also be beneficial for improving stride length.

Long-term trials indicate that resistance training and overspeed (downhill) running but not resisted sprint training can increase stride frequency. Overspeed (downhill) running seems most effective when using a 5.8 degree decline.

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GROUND CONTACT TIME AND FLIGHT TIME

PURPOSE

This section sets out the research relating to ground contact and flight times.

BACKGROUND

Introduction

Sprint running comprises a ground contact phase and a flight phase. During the ground contact phase, the sprinter absorbs braking and vertical forces and then produces vertical and propulsive forces to drive themselves forwards. During the flight phase, the sprinter repositions the limbs for the next ground contact phase.

CORRELATIONS BETWEEN FLIGHT TIMES AND SPRINTING RUNNING SPEED

Introduction

There are two main ways to analyse the effects of changing flight time with changing running speed. Firstly, flight time can be measured at different constant running speeds performed by a group of individuals (called “within individuals”). Correlations can then be drawn to assess the nature of the relationship between flight time and running speed. This tells us whether running faster involves shorter flight times. Secondly, flight time can be measured at maximal sprint running speed between the individuals in a population (called “between individuals”). Correlations can then be drawn to assess the nature of the relationship between flight time and running speed. This tells us whether faster runners display shorter or longer flight times. Since both approaches are cross-sectional, however, neither really help us assess whether shorter flight times are a side effect of faster running or whether being able to run using shorter flight times makes you run faster.

Within individuals

In investigations comparing sub-maximal running speeds within individuals, some researchers have found that flight times are shorter at faster running speeds (Nilsson et al. 1985; Mero and Komi, 1987; Kyröläinen et al. 2001; Kivi et al. 2002; Kuitunen et al. 2002; Dorn et al. 2012). In a musculoskeletal modelling study, Dorn et al. (2012) found that flight time increased with increasing running speed to a peak at 7m/s but decreased sharply thereafter. The implications of this finding are unclear.

Between individuals

In investigations comparing maximal running speeds between individuals, some researchers have found that flight time does not appear to be affected by running speed. Weyand et al. (2000) reported that flight time was relatively constant between runners of varying abilities, which they interpreted to suggest that the ability to reposition the legs during swing may not be a key factor in determining sprinting performance. Hunter et al. (2004b) performed a paired group analysis with a long stride-length group and a short stride-length group and found that the long stride-length group produced their longer stride length by means of a longer flight time. But they also found that there were no significant differences in sprint running performance between the two groups. This may indicate that longer flight times could simply be a feature of those athletes who display a sprinting style involving longer stride lengths and it may not necessarily be a factor that is related to sprint running velocity. Recently, Morin et al. (2012) reported that flight time was inversely correlated with sprint running performance, and that stride frequency was positively correlated with sprint running performance, both when assessed as peak sprint running velocity and as 100m sprint running time. Similarly, Lockie et al. (2013) assessed the relationship between flight time and 10m sprint running performance and found an inverse relationship, with longer flight times being associated with better ability.

CORRELATIONS BETWEEN SPRINTING SPEED AND GROUND CONTACT TIMES

Introduction

There are two main ways to analyse the effects of changing ground contact time with changing running speed. Firstly, ground contact time can be measured at different constant running speeds performed by a group of individuals (called “within individuals”). Correlations can then be drawn to assess the nature of the relationship between ground contact time and running speed. This tells us whether running faster involves shorter ground contact times. Secondly, ground contact time can be measured at maximal sprint running speed between the individuals in a population (called “between individuals”). Correlations can then be drawn to assess the nature of the relationship between ground contact time and running speed. This tells us whether faster runners display shorter ground contact times. Since both approaches are cross-sectional, however, neither really help us assess whether shorter ground contact times are a side effect of faster running or whether being able to run using shorter ground contact times makes you run faster.

Within individuals

Many studies investigating the effects of different running speeds in the same population have shown that ground contact times reduce substantially from slower to faster running speeds (Nilsson et al. 1985; Mann, 1986; Munro et al. 1987; Kyröläinen et al. 1999; Weyand et al. 2000; Kyröläinen et al. 2001; Kivi et al. 2002; Kuitunen et al. 2002; Nummela et al. 2007; Lockie et al. 2011; Brughelli et al. 2011; Morin et al. 2012; Lockie et al. 2013). Few, if any studies, have found that ground contact times do not reduce with faster running speeds.

Between individuals

Most studies have shown that shorter ground contact times are seen in faster subjects compared to slower subjects (Mann, 1986; Weyand et al. 2000; Morin et al. 2012; Lockie et al. 2013) but this is not always the case (Brughelli et al. 2011). Also, Taylor and Beneke (2012) reported data for the 3 top-finishing athletes in the 100m World Athletics Championship final of 2009. They noted that the mean ground contact times for Usain Bolt, Tyson Gay, and Asafa Powell were: 0.091 ± 0.001s, 0.070 ± 0.001s, and 0.080 ± 0.001s. In other words, ground contact time ranged between 70 – 90ms in these athletes in this event. The athlete who displayed the longest ground contact time (Usain Bolt) ran faster than the athlete who displayed the shortest ground contact time (Tyson Gay). This difference in ground contact time between the two athletes occurred because Usain Bolt ran the 100m in a smaller number of total strides (i.e. his stride frequency was lower) because of his greater stature and subsequently greater stride length. Both Beneke and Taylor (2010) and Krzysztof and Mero (2013) have suggested that the superior performances of Usain Bolt could be explained by his exceptional physique that enables him to increase his ground contact time by displaying a longer stride length and a shorter stride frequency than his peers. Indeed, Babić et al. (2007) have shown that taller individuals do take longer strides during running. Smaller stride frequency means that Bolt enjoys longer ground contact times and therefore has a longer period of time in which to display ground reaction forces, thereby producing a greater impulse with each stride. Moreover, Kugler and Janshen (2010) found that prolonging ground contact time led to greater propulsive forces during accelerative sprint running. This larger impulse produced with each stride is likely what leads to Bolt’s superior sprint running speed.

TRAINING TO REDUCE FLIGHT TIME OR GROUND CONTACT TIME

Flight time

Introduction

On the basis that there is no clear benefit to deliberately trying to reduce flight time, it seems probable that training modalities designed with this purpose might not be effective. For example, resistance training for the hip flexors is often performed with the intention of increasing the ability of sprinters to reposition their limbs during the flight phase, in order to reduce flight times. Despite such concerns, research indicates that increasing hip flexion strength may in fact be beneficial for sprint running performance. Deane et al. (2005) found that an 8-week hip flexor resistance-training program in untrained subjects produced significant reductions in 40-yard and shuttle run times by 3.8% and 9.0%, respectively, along with a 12.2% increase in hip flexion strength. The training program utilized a  standing hip flexion exercise with resistance bands, which primarily strengthens the hip flexor in the top half of the hip flexion range of motion. Whether this training program was effective in improving sprint running performance because it helped reduce flight time or through another mechanism, however, remains unclear.

Support for hip flexor training

While the mechanisms underlying the beneficial effects of hip flexor training on sprint running performance are unclear, there are additional (albeit only observational) grounds for thinking that training this muscle group is likely to be beneficial. The magnitude of hip flexion strength, moment or power has been positively correlated with sprint running performance in a number of cross-sectional investigations (Guskiewicz et al. 1993; Blazevich and Jenkins, 1996; Copaver et al. 2012). Guskiewicz et al. (1993) reported that both relative hip flexion and relative hip extension torque at 60 and 240 degrees/second were significantly correlated to 40 yard sprint times. Blazevich and Jenkins (1996) reported that hip flexion torque at all angular velocities was a better predictor of sprint running ability than hip extension torque. Copaver et al. (2012) reported that hip flexion power was positively correlated with sprint running performance over both 50m and 120m.

Effective mechanisms for hip flexor training

As noted above, the beneficial effects of hip flexor training on sprint running performance may be mediated by reductions in flight time or through other mechanisms. It is commonly believed that increasing hip flexion strength allows a faster repositioning of the limb in the flight phase, a shorter flight phase and consequently a faster stride frequency. Whether this is the case or not, it seems that faster sprint running speeds do require greater hip flexion strength. Acute analyses of biomechanics have reported that peak hip flexor moments increase significantly with increasing running speed when running above speeds of 7m/s (Schache et al. 2011). In addition, the iliopsoas (a hip flexor), along with the gluteus maximus and hamstrings (the main hip extensors), has been found by musculoskeletal modelling to be a primary muscle responsible for increasing speed via increases in stride frequency when running above speeds of 7m/s (Dorn et al. 2012). One potentially confusing factor in relating increased hip flexion strength to improved sprint running performance is the behavior of the rectus femoris, a hip flexor and also a knee extensor. The rectus femoris has been shown to produce hip extension during sprint postures (Hernandez et al. 2008) and gait (Hernandez et al. 2010), and exhibits a first peak in muscle activity during running in the middle of the stance phase that is roughly half of its second peak in muscle activity during the swing phase (Jönhagen et al. 1996). However, when expressed as a percentage of maximum voluntary isometric contraction, the rectus femoris does not appear to contract to high capacities during sprinting (Kyröläinen et al. 1999; Kyröläinen et al. 2005). Consequently, whether hip flexor training improves sprinting via increased hip flexion power and limb repositioning, or  via increased hip extension power and horizontal ground reaction force production, or via a combination of both, remains to be shown.

Ground contact time

Although it is not strictly possible to draw the inference of cause and effect from correlational studies, some researchers and coaches have interpreted the early findings to imply that deliberately reducing ground contact time might be valuable for improving sprint running speed. However, it seems very likely that longer ground contact times allow athletes who have naturally longer stride lengths to display superior ground reaction forces and impulses with each stride, it seems more probable that shorter ground contact times are a side-effect of faster sprint running speeds, rather than the cause of faster sprint running speeds. Indeed, many researchers have found that greater ground reaction forces are significantly correlated with faster sprint running speeds (see review by Randell et al. 2010). Weyand et al. (2000) discerned that as running speed increased, ground contact times decreased at a relatively greater rate, which they interpreted as leading to the length of ground contact time being too short to allow the leg extensors to develop maximum force. They therefore suggested that the limiting factor in sprinting speed is governed by the force-velocity relationship and is likely therefore muscle fiber contraction velocity. Essentially, ground contact times reduce with increasing sprint running speed because of the increasing muscle contraction velocity, but at the point where insufficient force can be produced at this muscle contraction speed, sprint running speed stops increasing and maximum velocity is reached.

IMPLICATIONS FOR TRAINING

Assuming that the shorter ground contact times that are observed with faster running speeds are a side-effect of the faster sprinting velocity and not the cause, as seems most likely, this implies that training methods that are designed to deliberately reduce ground contact times are likely to be highly counter-productive for sprint running performance. In contrast, training methods designed to increase maximal force production at high velocities are likely to be very beneficial.

CONCLUSIONS REGARDING SPRINTING

Sprint running comprises a ground contact phase and a flight phase. In the ground contact phase, the sprinter absorbs braking and vertical forces and then produces vertical and propulsive forces to drive themselves forwards. During the flight phase, the sprinter repositions the limbs for the next ground contact phase.

Training methods aiming to reduce ground contact or flight phase duration may not be effective. However, training methods aiming to improve hip flexion strength and power, or improve vertical and horizontal force production at high velocities are likely to be beneficial.

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JOINT ANGLE MOVEMENTS

PURPOSE

This section sets out the research relating to joint angle movements, including maximum joint angles and maximum joint angular velocities.

BACKGROUND

Introduction

In running, there have traditionally been two main ways of analyzing lower body joint movements: maximum joint angles and joint angle velocities. In respect of the maximum joint angles, the hip joint has been the main area of interest, with both maximum hip flexion and maximum hip extension being studied.

MAXIMUM JOINT ANGLES

Introduction

During running, the hip extends from late in the flight (swing) phase through the ground contact (stance) phase. Maximum hip extension angle appears to occur just before takeoff and maximum hip flexion appears to occur late in the flight phase (see review by Novacheck, 1998). Whether maximum hip extension angle increases with increasing running speed is unclear. Some studies have found that maximum hip extension angle does increase with increasing running speed (e.g. Kyröläinen et al. 1999) and good sprinters seem to exhibit greater maximum hip extension angle compared to average and poor sprinters (Mann et al. 2008), but others studies have reported that that maximum hip extension angle does not increase with increasing running speed (e.g. Franz et al. 2009). In contrast, maximum hip flexion angle does seem to increase with increasing running speed (Novacheck, 1998), and good sprinters seem to exhibit greater maximum hip flexion angle compared to average and poor sprinters (Mann et al. 2008).

Effect of hip joint angle on muscle lengths

As might be expected, the joint angles at various points within the gait cycle determine the muscle lengths. Schache et al. (2012) investigated the lengths of the hamstrings in various positions during the sprint running gait cycle. They found that the bi-articular hamstrings display a lengthening phase late in the flight phase followed by a shortening phase that commences just before foot-strike and continues throughout the ground contact phase. They reported that the biceps femoris (long head) is under the greatest strain during sprinting and they noted that this strain occurs during the terminal swing phase, which was also suggested by the findings of Chumanov et al. (2007).

Effects of pelvic tilt angle on muscle lengths

Research shows that the degree of anterior pelvic tilt can contribute to altered hamstring muscle lengths during running. Both Riley et al. (2010) and Chumanov et al. (2007) have reported that the relative tightness of the hip flexors contributes to the stretch of the contralateral hamstrings during running because of their effect on the degree of pelvic tilt at full hip extension. Chumanov et al. (2007) therefore stressed the importance of pelvic coordination in sprinting, and Riley et al. (2010) suggested that hip flexor mobility may therefore play a role in the utilization of hip extension range of motion during running. If contralateral hip flexor and hamstring flexibility are inextricably linked, then increasing the length and flexibility of either muscle will affect the other, though their effect on pelvic motion during sprinting may differ. In support of this proposal, Simonsen et al. (2012) reported that the hip flexion moment during the latter part of the stance phase in gait is mainly caused by passive elastic structures resisting hip joint extension. This may imply that increasing hip flexor mobility could not only affect the usable amount of hip extension range of motion but could also have a beneficial effect on sprint running performance. Interestingly, Sandberg et al. (2012) reported that acute stretching of the hip flexors led to greater vertical countermovement jump heights in trained subjects. It was proposed that this improvement might have arisen from increased neural drive to the agonist, decreased neural drive to the antagonist, reduced stiffness of the antagonist and braking forces to the agonist, or a combination of these factors, although no changes in muscle activity were observed. While jumping and running are not identical movements, similar mechanisms might be relevant for sprint running. However, Schache et al. (2000) found no significant correlation between static hip extension flexibility and peak hip extension range of motion during running, although it was reported that hip extension and anterior pelvic tilt are strongly correlated and coordinated in gait and in this context it is noteworthy that good sprinters exhibit greater maximum hip extension angle compared to average and poor sprinters (Mann et al. 2008).

Implications for preventing hamstring injury

Large changes in muscle length of the hamstrings during sprint running are consistent with reports that the biceps femoris (long head) is the most frequently injured hamstring muscle in athletes (e.g. Garrett et al. 1989; De Smet and Best, 2000; Slavotinek et al. 2002). The hamstrings are clearly stretched to long lengths during the late swing phase of high-speed running when performing simultaneous hip flexion and knee extension. Consequently, some researchers have proposed that athletes could benefit from increasing hamstrings length to avoid muscle strain injury. In this respect, studies have found that both eccentric resistance training (for a review, see Brughelli and Cronin, 2007) and stretch-shortening cycle resistance training in a lengthened position (e.g. Aquino et al. 2010; Guex et al. 2013) can increase the length of hamstrings muscles. Indeed, such exercises are regularly used in hamstring strain rehabilitation programs (e.g. Askling et al. 2013).

Implications for training

The precise implications for training of the findings regarding maximum hip extension and hip flexion angles during running are unclear. However, it is apparent that at the start of the ground contact phase, at the point that the lead foot touches the ground, the hamstrings are functioning at relatively long muscle lengths. In contrast, at the same point in time, the gluteus maximus is functioning at a much shorter muscle length. Resistance training exercises often develop strength at specific joint angle ranges of motion depending upon their point of peak contraction. Therefore, these findings may be relevant for identifying the optimal resistance training exercises for training the hamstrings and gluteus maximus for optimal performance during sprint running. The hamstrings may benefit from being trained with exercises that involve a peak contraction at long muscle lengths, while the gluteus maximus may benefit from being trained with exercises that involve a peak contraction at short muscle lengths.

JOINT ANGULAR VELOCITIES

Introduction

The joint angular velocities at the hip and knee are very high during sprint running and increase with increasing running speed (Kivi et al. 2002). For example, Kivi et al. (2002) found that at 95% of maximum speed, hip extension and knee extension angular velocity averaged 666 and 1,165 degree/s respectively. Similarly, in 4 male sprinters, Bezodis et al. (2009) reported peak hip and knee extension angular velocities of 871 and 602 degrees/s, respectively. By way of comparison, Akkus (2012) recorded peak hip extension angular velocity of 450 degrees/s during the second pull of the snatch lift as performed by elite female weightlifters, Bobbert et al. (1986) reported peak hip and knee extension angular velocities of approximately 572 and 859 degrees/s respectively during countermovement jumps in team sports athletes, Escamilla et al. (2001) recorded a peak hip extension angular velocity of 121 degrees/s during 1RM back squats performed by elite powerlifters, Okkonen and Häkkinen (2013) recorded peak hip and knee angular velocities of 604 and 724 degrees/s during a block sprint start, 532 and 534 degrees/s during sled pulling with 10% body mass, 477 and 536 degrees/s during sled pulling with 20% body mass, 758 and 1,046 degrees/s during countermovement jumps, 642 and 961 degrees/s during countermovement jumps with 10% body mass, 587 and 907 degrees/s during countermovement jumps with 20% body mass, and 435 and 513 degrees/s during smith machine half-squats with 70% of 1RM loading.

THE HIP EXTENSOR THEORY

Introduction

Some researchers have suggested that joint range of motion or joint angular velocities during sprint running might be significantly correlated with faster sprint running performance. This concept has been expressed as the “hip extensor theory” (e.g. Mann and Sprague, 1980; Mann and Sprague, 1983; Wiemann and Tidow, 1995). In this theory, it is suggested that the major determinant of increased horizontal propulsive ground reaction forces and reduced braking ground reaction forces during the stance phase of gait is a high angular velocity of the thigh.

Supportive evidence

Introduction

The majority of evidence that has been cited in favor of the hip extensor theory is observational and aims to draw associations between the kinematic characteristics observed in faster sprinters and their performance. For example, Mann (1986) reported that faster sprinters tend to display a smaller range of motion at the hip in stance, strike the ground with the foot closer to the body’s center of mass, and minimize the forward velocity of the foot at foot-strike by increasing hip extension angular velocity and knee flexion angular velocity in the late part of the flight phase. Similarly, Mann and Herman (1985) reported that winning 200m sprint performances were associated with greater hip extension angular velocity during stance, higher knee flexion angular velocity at foot-strike, smaller foot to body touchdown distance and higher backward foot velocity at foot-strike. Mann et al. (2008) came to similar conclusions.

Criticism

In explaining the features of the hip extensor theory, Choh et al. (2010) proposed that they function in order to create the smallest possible reduction in horizontal force as a result of the impact (i.e. the smallest braking forces). However, in contradiction to this suggestion, Hunter et al. (2005) found that sprinters who have lower relative braking impulses are not faster runners and do not have greater hip extension or knee flexion velocities at touchdown compared with runners who have high relative braking impulses, while Kawamori et al. (2012) found that short distance (10m) sprint running performance was not significantly correlated with relative braking impulse. Additionally, Kugler and Janshen (2010) found that inclining the center of mass to a greater degree led to greater propulsive forces during acceleration sprinting, which might be expected to involve striking the ground with the foot further from the body’s center of mass.

Counter proposal

Consequently, at present it seems likely that faster peak hip extension angular velocities are not the determinants of either greater propulsive forces or lower braking forces. It seems more likely that any association is likely produced in reverse, with greater forces produced while in the ground contact phase leading to greater joint angular velocities. This may imply that resistance training exercises designed to enhance force production while in the ground contact phase is advantageous for improving sprint running ability.

CONCLUSIONS REGARDING SPRINTING

Faster peak hip extension angular velocities are probably not the determinants of either greater propulsive forces or lower braking forces but likely the result of greater forces produced in the ground contact phase. Resistance training exercise designed to enhance force production while in the ground contact phase may therefore be valuable.

Since ground contact occurs with the hamstrings lengthened and the gluteus maximus contracted, the hamstrings may benefit from being trained with exercises that involve a peak contraction at long muscle lengths, while the gluteus maximus may benefit from being trained with exercises that involve a peak contraction at short muscle lengths.

 

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GROUND REACTION FORCES

PURPOSE

This section sets out the research relating to ground reaction forces (both vertical and horizontal) and impulse (both vertical and horizontal). Impulse is simply the product of force and time, which is equivalent to the change in momentum of an object.

BACKGROUND

Introduction

During running or sprint running, the gait cycle can be subdivided into a flight phase (when neither foot is on the ground) and a stance phase (when one foot is on the ground). In the stance phase, the athlete applies force into the ground in order to continue moving. These forces are properly called “ground reaction forces” but in this section they will be referred to simply as “forces”. No forces are applied in the flight phase. In biomechanics, it is conventional to analyze the overall resultant forces into their orthogonal components, in this case: vertical and horizontal. Since gravity acts on all runners and sprinters, their center of mass falls during the flight phase, accelerating back towards the ground. Substantial vertical forces are then required during the subsequent stance phase to raise the center of mass back upwards. Additionally, since the act of touchdown on the ground with the forefoot is not frictionless, there are horizontal braking forces that cause a slowdown at the start of every stance phase, which must then be reversed towards the middle and end by horizontal propulsive forces in order that the athlete can continue moving at the same speed (or indeed accelerate).

Relative importance of vertical and horizontal forces

Since gravity exerts an extremely large force, the vertical forces required to raise the center of mass during each stance phase are also very large (typically around 2,000N). This has led many researchers and coaches to believe that the ability to exert a large vertical force is critical for improving sprint running ability. On the other hand, since sprint running occurs against friction and wind resistance in a horizontal direction and no amount of vertical force can move an object in a horizontal direction, other researchers and coaches believe that even though horizontal forces are smaller, they are more important for sprinters than vertical forces.

CORRELATIONS BETWEEN FORCES OR IMPULSES AND RUNNING SPEED

Introduction

Some researchers have attempted to identify the associations (correlations) between either vertical or horizontal force production (or the associated impulses) and sprint running performance. This can be done using cross-sectional study designs of two basic kinds. Firstly, the study can compare the vertical or horizontal force (or impulse) production between subjects of differing abilities. This allows us to assess whether superior sprinters display higher vertical and/or higher horizontal forces (or impulses) than inferior sprinters. Secondly, a study can compare the vertical or horizontal force (or impulse) production within subjects who run at different sub-maximal or maximal speeds. This allows us to assess whether individuals display higher vertical and higher horizontal forces (or impulses) when running at faster speeds than when running at slower speeds.

Single force (or impulse) studies

Some investigations have only measured one component of force, which makes their ability to identify the relative importance of either component very limited. Weyand et al. (2000) performed a correlation analysis between the vertical (but not horizontal) forces in 33 runners during level treadmill running. The vertical forces were found to be significantly greater for faster runners than for slower ones and the relationship between vertical force and running speed was low-to-moderate (r = 0.39). Similarly, Buchheit et al. (2014) analysed the horizontal forces in 86 highly-trained youth soccer players (aged 14.1 ± 2.4 years) from an elite academy. In this study, rather than use a treadmill or force plate for measuring the forces, a new field method was used to measure horizontal forces, as described by Samozino et al. (2013). Relative horizontal force was found to be significantly correlated with accelerative sprint performance (10m) but not maximum sprint performance. Although these studies demonstrate the existence of a relationship between both vertical and horizontal force components and running speed, they cannot be used to compare the relative importance of vertical and horizontal forces.

Two force (or impulse) studies

Introduction

Fortunately, several studies have performed correlation analyses in which both vertical and horizontal forces (or impulses) have been measured, allowing us to compare their relative importance. For ease of comparison, these are divided into studies in which the vertical and horizontal forces (or impulses) were measured during an accelerating sprint and studies in which the vertical and horizontal forces (or impulses) were measured during constant speed running or constant maximum speed sprinting. Note that the vertical and horizontal forces (or impulses) are sometimes but not always measured during the same test as the sprint running performance, particularly where an instrumented treadmill is used (e.g. Funato et al. 2000; Morin et al. 2011a; Morin et al. 2012).

Accelerating running
INTRODUCTION

Several studies have assessed the correlation between running speed and forces (or impulses) during accelerating running (Mero, 1984; Morin et al. 2011a; Morin et al. 2012; Kawamori et al. 2012; Lockie et al. 2013; Morin et al. 2015). Such studies can be subdivided into those that have measured vertical and horizontal forces (or impulses) on a treadmill (usually non-motorised) and those that have measured vertical and horizontal forces (or impulses) with a force platform.

TREADMILL MEASUREMENTS

Although some commentators have criticized the use of a non-motorised treadmill for measuring sprint running performance, Mangine et al. (2014) have since found that performance on a 30m ground-based sprint and performance on a non-motorised treadmill test are very closely related. Morin et al. (2011a) analysed 12 male subjects (10 physical education students and 2 national-level long jump competitors). With both peak sprint running velocity and actual 100m sprint running performance, there were significant and strong relationships with horizontal (r = 0.736 and r = 0.775) but not vertical forces recorded during an 8-second sprint on a non-motorised treadmill. As a follow-up to verify these findings, Morin et al. (2012) analysed 13 male subjects with different sprint performance levels (9 physical education students, 3 national-level sprinters, and 1 world-class sprinter). For peak sprint running velocity, there were significant, moderate-to-strong relationships with both vertical (r = 0.593) and horizontal (r = 0.793) forces recorded during a 6-second sprint on a non-motorised treadmill. However, for actual 100m sprint running performance, there was only a significant and strong relationship with horizontal (r = 0.834) forces.

OVERGROUND MEASUREMENTS

In an early study, Mero (1988) analysed 10 Finnish sprint athletes who performed short maximal sprints over 10m from the blocks. The researchers found no correlation between mean or peak vertical forces in the first step and 10m sprinting speed. However, there was a significant, moderate correlation (r = 0.56) between mean and peak horizontal forces in the first step (r = 0.63 and r = 0.66) and 10m sprinting speed. Nevertheless, this study was limited as forces were only measured during the first step. Kawamori et al. (2012) analysed 30 physically active males with a team sports background who performed short maximal sprints over 10m over a force platform. Sprint running time was significantly and moderately correlated with the relative net horizontal impulse (r = 0.52) and the relative propulsive horizontal impulse (r = 0.66) at 8m but not with the relative vertical impulse. Lockie et al. (2013) analysed 22 healthy men currently participating in field sports who performed short maximal sprints of 10m over a force platform. Measurements were taken at three contact points (first, second and final) and correlated with sprint running speed from 0 – 5m, 5 – 10m, and 0 – 10m. There was a significant correlation only between vertical force and sprint running speed from 5 – 10m (r = 0.405). All other correlations were not significant. Most recently, Morin et al. (2015) took multiple measurements over a 40m sprint. They found that net horizontal impulse and propulsive horizontal impulse were significantly and closely correlated with 40m mean speed (r = 0.868 and r = 0.802, respectively) but vertical impulse and braking horizontal impulse were not.

Constant speed running

Several studies have assessed the correlation between running speed and forces during constant speed running (Kyröläinen et al. 1999; Funato et al. 2000; Nummela et al. 2007; Brughelli et al. 2011). Kyröläinen et al. (1999) analysed 17 endurance running athletes who ran on a 200m indoor track for 3 minutes at 3.25, 4.00, 4.75, 5.25, and 5.75m/s. They used stepwise regression analysis and found that mean horizontal force in the propulsion phase was the main factor explaining (88.2%) running velocity, while mean horizontal force in the braking phase also had a small explanatory role (10.6%). Mean vertical force did not explain the differences in running velocity. Funato et al. (2000) analysed 10 normal sedentary men (aged 29.8 ± 7.8 years) who used an instrumented treadmill to perform 6 different constant-speed tests: slow walking, fast walking, slow running, medium running, fast running, and maximal effort sprinting. The subjects also performed a ground-based 50m sprint running test. There was a moderately-strong correlation between the 50m sprint time and horizontal force (r = 0.683). Nummela et al. (2007) analysed 25 endurance athletes who performed 30m ground-based runs at a range of 8 different speeds from 4m/s to maximal sprint running. The researchers found no correlation between relative vertical force and running speed but there was a significant, moderate correlation (r = 0.56) between relative horizontal force and running speed. More recently, Brughelli et al. (2011) analysed 16 semi-professional Australian Rules football players performing short runs at 40% to 100% of maximal speed. For peak sprint running velocity, there was a significant, moderate relationship with horizontal (r = 0.49) but not vertical force.

CHANGES IN GROUND REACTION FORCES WITH INCREASING RUNNING SPEED

Direct comparison of vertical and horizontal forces

Many studies have recorded simultaneous changes in vertical and horizontal forces (measured in Newtons) in conjunction with changes in running speeds (Munro et al. 1987; Nilsson et al. 1989; Nummela et al. 1994; Kuitunen et al. 2002; Kyröläinen et al. 2001; Belli et al. 2001; Kyröläinen et al. 2005; Nummela et al. 2007; Brughelli et al. 2011). The following chart shows the difference between the relative changes in vertical and horizontal forces for these studies, where absolute data is available.

Sprinting forces

Role of vertical forces

If horizontal forces are more relevant to an understanding of which athlete can sprint faster than another, then what is the role of vertical force? Given the very large size of the vertical forces involved, they are unlikely to be irrelevant. One possible explanation is the existence of a non-linear relationship between increasing running speed and vertical forces. Brughelli et al. (2011) found that peak vertical forces on a non-motorized treadmill increased up to 60% of maximum velocity but remained constant above this level. On the other hand, peak horizontal forces were found to increase linearly with increasing speed from 40 – 100% of maximum velocity. This may be related to the “strategy shift” observed by Dorn et al. (2012). Dorn et al. (2012) showed that above 7m/s, effective vertical impulse decreased and a strategy shift occurred in sprinting, whereby the gastrosoleus muscles could no longer produce greater vertical forces as a result of their limited contraction times. Faster speeds were therefore brought about by accelerating the hip and knee joints more rapidly and producing greater stride frequencies.

Forces during sprinting drills

On the basis that improving the ability to produce horizontal forces might be valuable for sprinters, some researchers have explored the acute forces during different sprint running drills. For example, Mero and Komi (1994) found that compared to sprinting, hopping induced greater braking and vertical forces and bounding induced greater propulsive and vertical forces, but sprinting produces far greater power braking and propulsive power outputs than hopping and bounding. Weyand et al. (2005) found that backward sprinting produced similar vertical forces compared to forward sprinting, but one legged hopping produced significantly greater vertical forces and hip, knee, and ankle extensor muscle forces, albeit at much slower speeds and with greater ground contact time. This indicates that these exercises could be useful in developing greater sprint qualities. However, without long-term studies, it is impossible to be certain regarding their benefits.

TRAINING USING VERTICAL OR HORIZONTAL EXERCISES

Introduction

To date, very little work has been performed to assess whether vertically-oriented or horizontally-oriented resistance training, ballistic training, or plyometrics exercises are better for improving sprint running ability and most assessments of which type of exercises is likely to be best rest upon an understanding of the biomechanics of sprint running. Examples of vertically-oriented resistance training, ballistic training, and plyometrics exercises include back squats, jump squats, and depth jumps. Examples of horizontally-oriented resistance training, ballistic training, and plyometrics exercises include hip thrusts or heavy sled pushes, sled towing, and broad jumps or bounding.

Long-term trials

One long-term trial of vertical and horizontal exercises found that they are similarly effective in untrained subjects (Singh and Singh, 2013). One low-volume comparison of vertical and combined (vertical and horizontal) exercises found that they were similarly ineffective in highly-trained professional male soccer players (Los Arcos, 2014). And another comparison of vertical resistance training exercise and combined (vertical resistance training exercise and both vertical and horizontal plyometrics) found that they were they were similarly ineffective in highly-trained professional male soccer players (Rønnestad et al. 2008). Consequently, it is clear that direct trials comparing either vertical and horizontal resistance training exercises and either vertical and horizontal plyometrics are needed.

CONCLUSIONS REGARDING SPRINTING

Horizontal forces appear to increase to a much greater extent with increasing running speeds than vertical forces. Consequently, it seems likely that the ability to produce horizontal force may be more valuable to an athlete intending to sprint faster than the ability to produce vertical force.

Vertical forces are very high during sprint running and may increase to a plateau where a strategy shift occurs. Consequently, the ability to produce vertical force may also be a requirement for sprint running performance.

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JOINT MOMENTS

PURPOSE

This section sets out the research relating to joint moments during sprinting.

BACKGROUND

Introduction

The greater ground reaction forces that likely lead to faster sprint running speeds are caused by greater joint moments. However, it is unclear exactly how and when the various muscle forces are produced that lead to each joint moment being produced at each point in the gait cycle.

Roles of each joint moment

Several studies have assessed the relative importance of each of the leg muscles to sprint running performance by investigations of the joint moments. Many of these studies have concluded that the hip is of primary importance. Mann and Sprague (1983) identified that the hip extensors and knee flexors are dominant in terminal swing, through the foot-strike phase and into mid-stance. They concluded that the hip extensors and knee flexors are responsible for pulling the body over the touchdown leg with minimal loss of horizontal speed. Mann and Sprague (1983) concluded that greatest contributor to sprint running performance was the muscular activity at the hip. They suggested that a large hip extension moment was generated at foot-strike and in the early part of the stance phase, which they proposed both minimized braking forces and provided horizontal propulsive forces. Mann (1981) also reported that the best sprinters had the greatest hip extensor and knee flexor moments. Bezodis et al. (2008) and Bezodis et al. (2009) both remarked upon the large hip extension moments that occurred during sprint running. And a computer model built by Dorn et al. (2012) predicted that increases in force from the hip flexors (iliopsoas) and hip extensors (hamstrings and gluteus maximus) were responsible for increases in running speeds above 7m/s.

Joint moments with increasing speed

As might be expected, the various net joint moments change with increasing running speed. Interestingly, the increases observed for hip extension are substantially greater than those observed at the knee (Simpson and Bates, 1990; Belli et al. 2001; Kuitunen et al. 2002; Schache et al. 2011), which indicates that the hip extensors are very likely the most important muscles for sprint running performance and therefore training practices should emphasize their development above other leg muscles. The following chart shows the findings of those studies that reported absolute data.

Sprinting joint moments

Sequential kinetic linking

Although it is clearly a vital concept, only a small number of studies have investigated the possibility of sequential kinetic linking during sprint running. Nevertheless, there is evidence to suggest that the pattern of sequential kinetic linking does occur in sprint running. In sequential kinetic linking, joint power follows a proximal-to-distal sequence that begins with the hip. The proximal-to-distal sequence has been investigated in various sports in respect of upper body movements and appears to be involved in most throwing and striking motions, as Wagner et al. (2012) have shown. Hunter et al. (2005) concluded that in the acceleration phase of sprinting, athletes use a proximal-to-distal sequence in which peak extension velocity was first reached by the hip, then the knee and finally the ankle joint. Johnson and Buckley (2001) similarly concluded that there is first a generation of peak extensor power at the hip, followed by the knee and then the ankle during stance.

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FACTORS INFLUENCING NET JOINT MOMENTS: MUSCLE MOMENT ARMS

Introduction

Internal net joint moments are the product of muscular force production and the length of the muscle moment arm. Muscle force is a function of muscular size and a range of other central and peripheral factors. Muscle moment arms vary according to the individual and according to the joint angle and have rarely been investigated in direct relation to sprint running.

 

Hamstrings

Few studies have reported on the moment arms for the hamstrings in hip extension. Dostal et al. (1986) reported that the moment arms were 5.6cm for the semitendinosus, 4.6cm for the semimembranosus, and 5.4cm for the biceps femoris (long head). Németh and Ohlsén (1985) reported a moment arm for all hamstrings of 6.1cm. These figures indicate that the hamstrings are an effective hip extensor in the anatomical position. More importantly, Schache et al. (2012) reported that the sagittal plane moment arm of the biceps femoris (long head) is 20 – 49% greater at the hip and 42 – 94% greater at the knee in a typical terminal swing pose compared to the anatomical position.

Gluteus maximus

Few studies have reported on the moment arms for the gluteus maximus in hip extension. Dostal et al. (1986) reported that the hip extension moment arm of the gluteus maximus was was around 4.5cm. This value is similar to those reported by Blemker and Delp (2005) who built a three-dimensional musculoskeletal model and found that the moment arm length of the gluteus maximus ranged between 1.5 – 6.5cm, with a median value of c. 4cm. However, it is substantially less than the value reported by Németh and Ohlsén (1985), who reported that the moment arm length of the gluteus maximus in hip extension was around 8cm. More importantly, Nemeth and Ohlsén (1985) reported that moment arm lengths averaged were far greater in the anatomical position than in 90 degrees of hip flexion (8cm vs. 3cm), which suggests that we might expect the gluteus maximus to be more easily activated when at short lengths than at long lengths, which is exactly what occurs. Worrell et al. (2001) reported that during dynamometry testing although the hip extension moment increased with increasing hip flexion, gluteus maximus muscle activity decreased with increasing hip flexion. Gluteus maximus muscle activity increased from 64% of maximum voluntary isometric contraction (MVIC) levels at 90 degrees of hip flexion to 94% of MVIC at 0 degrees. This indicates that the activity of the gluteus maximus may also be reduced during the terminal swing phase (when the hip is in flexion) in comparison with during the mid-to-late stance phase (when the hip is in full extension).

Comparing hip extensors

Exactly how the moment arm lengths of the hamstrings compare with the gluteus maximus in hip extension is somewhat unclear. In the anatomical position, Dostal et al. (1986) reported that the moment arm length of the gluteus maximus was shorter than that of the hamstrings. On the other hand, in the same position, Németh and Ohlsén (1985) reported the opposite finding. It seems likely that the hamstrings and gluteus maximus therefore have similar muscle moment arms to one another and are therefore expected to be involved in hip extension to a similar extent. It is perhaps more relevant that when the hip is in the terminal swing position (i.e. hip flexion), the hamstrings moment arm length is increased, and when the hip is in the mid-to-late stance position (i.e. full hip extension), the gluteus maximus moment arm is maximized.

FACTORS INFLUENCING NET JOINT MOMENTS: MUSCLE FORCE

Introduction

Muscular force is affected by several factors, including the contraction speed, starting muscle length, muscle fiber type, contraction velocity, degree of activation, cross-sectional area (size), pennation angle and normalized fiber length. However, in general, it is widely recognised that the most significant factor affecting muscular force-producing capacity when the available time for force production is <300ms is contraction velocity, or the force-velocity relationship. Indeed, Weyand et al. (2000) concluded that the limiting factor in sprint running speed may well be muscle fiber contraction velocity and Beneke and Taylor (2010) ascribe the unique success of Usain Bolt to his ability to exert more force over longer ground contact times, thereby manipulating the force-velocity relationship. These conclusions are supported by the findings of Miller et al. (2012) who built a musculoskeletal model of human sprint running that included various equations modelling the force–velocity, excitation–activation, length-tension, and series elastic force–extension relationships. In this model, it was found that the force–velocity relationship had the greatest limiting effect on maximum speed.

 

The force-velocity relationship

The primary importance of the force-velocity relationship for muscle force production during sprint running has two key implications. Firstly, it implies that the ability to produce maximum force is likely to be a key predictor of sprint running ability (since greater maximum force producing ability means more force can be produced at faster velocities). Secondly, it implies that faster muscle contraction velocity is also likely to be a key predictor of sprint running ability (since greater muscle contraction velocity also means more force can be produced at faster velocities). There are many factors (both central and peripheral) that affect the ability to produce maximum force. Muscle contraction velocity is dependent primarily upon muscle fiber type and muscle fascicle length. Type II muscle fibers contract several times quicker than type I muscle fibers and since the sarcomeres in a muscle fiber contract simultaneously, longer muscle fascicles have faster shortening velocities.

CORRELATIONS BETWEEN MUSCLE SIZE AND SPRINTING SPEED

Some studies have reported that there are relationships between overall muscular size and sprint running performance. Weyand and Davis (2005) reported that in successful track athletes, muscle mass was closely matched to the vertical ground reaction forces required for running at the event speed. However, in contrast, Morin et al. reported that body mass index (BMI) showed no significant correlation with 100m sprint running performance in elite track sprinters. In respect of specific muscles, Abe et al. (2000) and Kumagai et al. (2000) both found that the muscle sizes of the quadriceps and gastrocnemius were significantly correlated with faster sprint running performance. Similarly, Kubo et al. (2011) found that erector spinae and quadratus lumborum muscle sizes contributed to accelerative sprint running  performance in youth soccer players. A more complex relationship was observed by Hoshikawa et al. (2006), who found that in both male and female junior sprinters, greater development of the psoas major relative to the quadriceps cross-sectional area was correlated with 100m race performance and that in male junior sprinters, larger quadriceps cross-sectional area was in fact negatively correlated with performance. The sex differences in this study might be explained by differences in the size of the psoas, which is much smaller in females (Hoshikawa et al. 2011). The negative correlation between quadriceps cross-sectional area and sprint running performance may be related to the inertial properties of the lower body. Royer and Martin (2005) reported that increasing mass of the lower limb causes increases in the energy cost of walking. It seems likely that similar increases in energy cost would be observed during running, given the similarity of gait between these two activities. Similarly, Browning et al. (2007) found that increases in mass of the lower limb increased the energy cost of walking to a greater extent than more proximal increases in mass, which suggests that if inertial properties are responsible for these observations, then greater mass of the plantar flexors might be even more detrimental for sprint running performance. However, this remains unclear at the present time.

CORRELATIONS BETWEEN MUSCLE FIBER TYPE AND SPRINTING SPEED

Although muscle fiber type is widely believed to be a key predictor of sports performance, the relationship between type II muscle fiber proportion and sprint running ability has only rarely been explored. Inbar et al. (1981) found that 40m sprint performance was significantly correlated with type II fiber proportion. Interestingly, a recent case study reported that a former 60m indoor sprint running world champion displayed highly unusual muscle fiber type characteristics (Trappe et al. 2015). It was reported that the athlete displayed a very high abundance (24%) of type IIx muscle fibers and a total type II muscle fiber population of 71% in the vastus lateralis, which is commonly reported to display a fairly balanced type I and type II muscle fiber type (Gouzi et al. 2013).

CORRELATIONS BETWEEN MUSCLE FASCICLE LENGTH AND SPRINTING SPEED

Some studies have reported that longer muscle fascicle lengths are associated with greater sprint running ability. Abe et al. (2000) reported that sprinters possessed longer fascicle length in the quadriceps and gastrocnemius muscles than either endurance runners or untrained controls subjects. However, they did not measure the fascicle length of any other muscles. Similarly, Kumagai et al. (2000) also reported that greater muscle fascicle length in quadriceps and gastrocnemius muscles were both significantly correlated with faster sprint running ability. However, again, they did not measure the fascicle length of any other muscles.

IMPLICATIONS FOR TRAINING

As noted above, the ability to produce force quickly is determined by two key factors, because of the force-velocity relationship: the ability to produce absolute force, and muscle contraction velocity. The central and peripheral factors that make up strength are highly complex, although muscle size is the single most important. The central and peripheral factors that make up muscle contraction velocity are less complex, and muscle fiber type and muscle fascicle length are the most relevant. Consequently, it seems that training methods aimed toward developing muscular size, shifts in muscle fiber type towards type II fibers, and increases in muscle fascicle length could well be advantageous for sprinters. The most common training method for developing muscular size is conventional, heavy-load resistance training, although other methods of training for improving muscular size may also be effective. Common training methods used to shift muscle fiber type toward type II fibers include high-velocity resistance training or ballistic training. Common training methods used to increase muscle fascicle length include eccentric training (Brughelli and Cronin, 2007)

CONCLUSIONS REGARDING SPRINTING

The ability to produce force quickly is critical for sprint running performance. High-velocity force production is superior in stronger athletes with higher proportions of type II muscle fibers and longer fascicle length.

Net hip extension moments increase most quickly with increasing sprint running speed. Consequently, the hip extensors (hamstrings and gluteus maximus) are likely the most important muscles for sprint running performance and training practices should therefore prioritise their development.

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STIFFNESS

PURPOSE

This section sets out the research relating to stiffness during sprinting.

BACKGROUND

Introduction

Stiffness is a measure of how much an object resists being lengthened. For sprint running, there are three main measures of stiffness: vertical stiffness, leg stiffness and joint stiffness (see reviews by Brughelli and Cronin, 2008a; Brughelli and Cronin, 2008b). Vertical stiffness is a measure of the stiffness of the center of mass of the human body. Leg stiffness differs from vertical stiffness in that it refers to the stiffness of the leg rather than of the center of mass. Joint stiffness is simply the ratio of joint moment to joint angular displacement.

Changes in stiffness with running speed

Vertical stiffness

The different types of stiffness measure appear to change to a different extent with increasing running speed. Vertical stiffness is perhaps the most straightforward to understand. In their reviews, Brughelli and Cronin (2008a; 2008b) concluded that at both low-to-moderate running speeds and at higher running speeds, vertical stiffness increases with increasing running speed.

Leg stiffness

Regarding leg stiffness, Brughelli and Cronin (2008a; 2008b) concluded that at low-to-moderate running speeds, leg stiffness remains constant despite increasing running speed. At higher running speeds, they concluded that it is unclear what happens to leg stiffness. In this context, it is relevant that Arampatzis et al. (1999) found that increases in leg stiffness occurred with increasing running speed that were predominantly caused by the known increases in knee joint stiffness.

Joint stiffness

In respect of the stiffness of the individual joints, Kuitunen et al. (2002) found that ankle joint stiffness remained constant but knee joint stiffness increased with increasing running speed. Kyröläinen et al. (1999; 2005) and Mero and Komi (1987) proposed that the increase in knee joint stiffness that is observed with increasing running speed was likely the result of increased co-activity of agonist and antagonist muscles just before foot-strike. And Belli et al. (2001) went so far as to propose that it was in fact the primary role of the knee extensors and plantar flexors to ensure a high degree of joint stiffness during sprint running, while the hip extensors provided the forward propulsion.

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Relationship between stiffness and running speed

Vertical stiffness

The relationship between the different leg, vertical or joint stiffness measures and sprint running performance is uncertain. Findings regarding vertical stiffness have been particularly conflicting. Chelly et al. (2001) found that vertical stiffness during repeated jumping was significantly correlated with the maximal sprint running speed over 40m. On the other hand, Bret et al. (2002) found that 100m sprint running performance was not significantly correlated with vertical stiffness. Similarly, when Taylor and Beneke (2012) compared the 4 fastest runners in in the 100m World Athletics Championship final of 2009, they found that although Usain Bolt displayed the greatest velocity over the 60 – 80m split, his vertical stiffness was significantly lower than that of the other 2 athletes. Therefore, it is unclear whether vertical stiffness is beneficial for sprint running performance.

CONCLUSIONS REGARDING SPRINTING

Vertical stiffness and knee stiffness increase with increasing sprint running, although what happens to leg stiffness is less clear.

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ELECTROMYOGRAPHY (EMG)

PURPOSE

This section sets out the research relating to electromyography (EMG) activity during sprinting.

BACKGROUND

Introduction

Many studies have addressed the nature of muscle activity during high-speed running, using electromyography (EMG) methods. Although there are many studies, interpretation is very difficult, because of the rapidly changing nature of the signal over the gait cycle.

ROLES OF THE KEY MUSCLES

Introduction

The most commonly-measured muscles for running and sprint running are the hip extensors (hamstrings and gluteus maximus), knee extensors (quadriceps), and plantar flexors (soleus and gastrocnemius). In investigating the role of the muscles using electromyography (EMG), researchers have used both fine wire and surface electrodes, although little differences have been observed between the two methods (Chumanov et al. 2012). Overall, it seems that most muscles display their highest level of activation either just before or just after ground contact (Mann et al. 1986; Novacheck, 1998), although there are some marked exceptions.

Hamstrings

Several researchers have identified the importance of the hamstrings in high-speed running by using EMG to measure muscle activity. Most studies have found that the largest peak in hamstrings muscle activity occurs in the terminal swing phase (Nilsson et al. 1985; Jacobs et al. 1993; Montgomery et al. 1994; Kuitunen et al. 2001; Higashihara et al. 2010; Chumanov et al. 2012; Rabita et al. 2013), although other studies have found that this peak occurs in the early stance phase (Mero and Komi, 1987; Kyröläinen et al. 1999; Belli et al. 2001) or across both terminal swing and early stance (Mann and Hagy, 1980; Mann et al. 1986; Jönhagen et al. 1996; Kyröläinen et al. 1999; Modica and Kram, 2005; Chung et al. 2009). These findings indicate that the hamstrings are likely primary propulsive muscles during high-speed running, and probably act by storing elastic energy during their lengthening muscle actions in the terminal swing phase, which is then released in the early stance phase (Simonsen et al. 1985; Jönhagen et al. 1996).

Gluteus maximus

Several researchers have identified the importance of the gluteus maximus in high-speed running by using EMG to measure muscle activity. Indeed, many studies have observed peaks in gluteus maximus muscle activity just after ground contact (Mero and Komi, 1987; Montgomery et al. 1994; Weinmann and Tidow, 1995; Belli et al. 2001; Kyröläinen et al. 2001; Rabita et al. 2013) or in the terminal swing phase (Nilsson et al. 1985) or both (Mann and Hagy, 1980; Simonsen et al. 1985; Mann et al. 1986; Jacobs et al. 1993; Jönhagen et al. 1996; Kyröläinen et al. 1999; Chumanov et al. 2012). These findings indicate that the gluteus maximus may also be an important propulsive muscle during high-speed running, and may act in a similar way to the hamstrings by storing elastic energy during its lengthening muscle action in the terminal swing phase, which is then released in the early stance phase (Simonsen et al. 1985; Jönhagen et al. 1996). However, it seems that the gluteus maximus is also very active during stance, which may indicate another role for the gluteus maximus in either forward propulsion or in vertical center of mass recovery (in conjunction with the quadriceps) during this phase.

Quadriceps

The role of the knee extensors during high-speed running may differ depending on whether they are single-joint (vastus lateralis, vastus medialis and vastus intermedius) or two-joint (rectus femoris). In respect of the vastus lateralis, some researchers have observed that the magnitude of the EMG signal rises to a peak in the terminal swing phase and that this peak remains into the early part of the stance phase before reducing (Mann and Hagy, 1980; Simonsen et al. 1985; Nilsson et al. 1985; Kyröläinen et al. 1999; Kyröläinen et al. 2001). Other researchers have noted that while vastus lateralis EMG activity increases in the terminal swing phase, the actual peak of the vastus lateralis EMG signal occurs in the stance phase (Mero and Komi, 1987; Jacobs et al. 1993; Montgomery et al. 1994; Belli et al. 2001; Rabita et al. 2013). When Kuitunen et al. (2002) investigated the vastus medialis, they observed slightly different results, which may reflect a slightly different function of the muscle. They noted a peak in the terminal swing phase that was already decreasing upon reaching the beginning of the stance phase. However, Rabita et al. (2013) did not find this and observed similar patterns of muscle activity in the vastus medialis and vastus lateralis. These findings seem to point to the role of the quadriceps as being central in early stance, where the vertical fall of the runner’s center of mass is arrested and reversed (i.e. shock absorption).

Rectus femoris

In contrast to the other quadriceps, the two-joint rectus femoris appears to display different characteristics during high-speed running. Most researchers have observed two peaks in activity: one peak of rectus femoris activity in line with the other quadriceps (early stance) and another peak when performing hip flexion (early-to-mid swing), which might be related to the function of the rectus femoris as a hip flexor (Mann and Hagy, 1980; Nilsson et al. 1985; Simonsen et al. 1985; Montgomery et al. 1994; Jönhagen et al. 1996; Modica and Kram, 2005; Chung et al. 2009; Rabita et al. 2013). In contrast to these findings, both Mero and Komi (1987) and Kyröläinen et al. (1999) found that the rectus femoris was not particularly active during either terminal swing or early stance but was highly active in late stance, at push-off.

Plantar flexors

Regarding the plantar flexors, many researchers have noted that the gastrocnemius is relatively inactive during the swing phase of high-speed running but begins increasing the magnitude of the EMG signal steadily through the terminal swing phase, reaching a flat peak precisely upon ground contact that remained for a substantial portion of the stance phase (Simonsen et al. 1985; Mann et al. 1986; Kyröläinen et al. 1999; Kyröläinen et al. 2001; Belli et al. 2001). Other researchers have found that plantar flexor EMG activity increases steadily through the terminal swing phase but does not peak until just after the beginning of the stance phase (Mann and Hagy, 1980; Mero and Komi, 1987; Jacobs et al. 1993; Jönhagen et al. 1996; Kuitunen et al. 2002; Modica and Kram, 2005; Chung et al. 2009; Rabita et al. 2013). Nilsson et al. (1985) found the reverse results, in that gastrocnemius EMG activity peaked in terminal swing before the start of the stance phase, where it subsequently dropped off markedly.

Role of pre-activity

Some researchers have investigated the role of increased muscle activity during the terminal swing phase of high-speed running, known as pre-activity. Specifically, it has been proposed that the purpose of the increased muscle activity in this phase is for increasing joint or leg stiffness (Kuitunen et al. 2002). Mero and Komi (1987) and Kyröläinen et al. (1999; 2005) all found that muscle activity levels upon foot-strike increase with running speed. They suggested that this greater pre-activation of the muscles is important in preparing the muscles to absorb the increased impact forces that are associated with increased running speeds, by making them stiffer.

CHANGES IN MUSCLE ACTIVITY WITH INCREASING RUNNING SPEED

Introduction

Muscle activity can change in three main ways with increasing running speed: it can increase in magnitude of the signal, it can alter its timing within the gait cycle, or it can increase its duration. Observing the way in which muscle activity changes with increasing running speed can help us understand which muscles are most important for running faster and which are less relevant.

Magnitude of muscle activity

Introduction

In general, the muscle activity of the lower body musculature (mainly the vastus medialis, vastus lateralis, biceps femoris, gluteus maximus, rectus femoris, soleus, and gastrocnemius muscles) increases with increasing running speed, as might logically be expected (Mero and Komi, 1986; Mero and Komi, 1987; Nummela et al. 1994; Kyröläinen et al. 1999; Kuitunen et al. 2002; Liebenberg et al. 2011).

 

Differences between muscles

Some researchers have observed that the various leg muscles increase their muscle activity with increasing running speed either by different amount or during different parts of the gait cycle. Both Kyröläinen et al. (1999) and Kyröläinen et al. (2005) found that the muscle activity of the hamstrings increased the most overall out of all the leg muscles with increasing running speed. Higashihara et al. (2010) reported that the muscle activity of the hamstrings increased with increasing running speed, but unfortunately they did not measure the activity of any other muscle group. Curiously, some researchers have found that the gluteus maximus displays markedly greater muscle activity in the terminal swing phase with increasing running speed, but actually reduced activity in early stance (Mann et al. 1986; Kuitunen et al. (2002). Nilsson et al. (1985) similarly noted that increasing running speed caused what appeared to be a shift of muscle activity in the gluteus maximus earlier in the gait cycle, which may be the same phenomenon. However, other researchers have not reported this phenomenon and rather have found that muscle activity of the gluteus maximus increases its magnitude of muscle activity in both terminal swing and early stance phases (Kyröläinen et al. 1999; Kyröläinen et al. 2001).

Duration of muscle activity

In respect of the duration of the signal, Wiemann and Tidow (1995) reported that the hamstrings display a longer lasting duration of muscle activity than the other muscles across the running gait cycle. More importantly, Kyröläinen et al. (2005) found that of all the leg muscles only the biarticular hamstrings increased the duration of their muscle activity with faster running speeds. Although some strength coaches have suggested that the erector spinae muscle group is important for sprint running performance, this does not appear to be the case. Mann et al. (1986) found that erector spinae muscle activity displayed a similar duration of activity for jogging, running, and sprinting.

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CHANGES IN MUSCLE ACTIVITY WITH INCREASING FATIGUE

Introduction

Muscle activity can change in three main ways with increasing fatigue: it can increase in magnitude of the signal, it can alter its timing within the gait cycle, or it can increase its duration. The most commonly-measured muscles for running and sprint running are the hamstrings, gluteus maximus, quadriceps, and plantar flexors.

Magnitude of muscle activity

In respect of the magnitude of the signal, Nummela et al. (1994) found that the muscle activity of the biceps femoris and gastrocnemius muscles was higher when non-fatigued than when fatigued during the propulsion part of the stance phase, despite running at the same speed. On the other hand, they noted that the muscle activity of the rectus femoris was was higher when fatigued than when non-fatigued during the braking part of the stance phase. The exact implications of these findings are unclear.

CONCLUSIONS REGARDING SPRINTING

The hamstrings and gluteus maximus display peaks in muscle activity in terminal swing, which implies that they probably act by storing elastic energy during their lengthening muscle actions in the terminal swing phase, which is then released in the early stance phase.

The quadriceps and calf muscles are highly active in early stance, which implies that they act primarily as shock absorbers. The two-joint rectus femoris may also help perform hip flexion in the early-to-mid swing phase.

Since the muscle activity of the hamstrings and gluteus maximus muscles increases most with increasing running speed, this implies that they are the most important muscles for high-speed running.

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TRANSFER TO TRAINING

PURPOSE

This section sets out the research relating to transfer of different exercises or training methods to sprinting speed.

BACKGROUND

Introduction

Various researchers have performed reviews into the effectiveness of common training methods for sprint running, with priority being given to the evidence that can be provided by long-term trials. In general, there is currently a general consensus among reviewers and researchers that no single training technique offers significantly greater benefits from any others and that a mixed approach is probably optimal (e.g. Behrens and Simonson, 2011; Sáez de Villarreal et al. 2012a, Lockie et al. 2011; Rumpf et al. 2012). This may reflect the fact that, owing to complex segment-interactions (Chumanov et al. 2007; Huang et al. 2013) and myofascial force transmission (Carvalhais et al. 2013; Gadikota et al. 2013), the body certainly utilises all of its parts as a unit to produce the greatest power outputs and sprinting speeds. Therefore, the various parts of the body need to be sufficiently strong, powerful, and coordinated for maximum speed performance.

Long-term trials: resistance training and ballistic training

In respect of conventional heavy resistance training and ballistic or high-velocity resistance training, Cronin et al. (2007) reviewed the literature and concluded that isoinertial measures of strength displayed significant longitudinal correlations with sprint running performance. This means that long-term improvements in resistance training exercises were associated with long-term improvements in sprint running times. However, Cronin et al. (2007) also concluded that it was not possible to specify whether heavy resistance training produced better results than power-based resistance training. Regarding cross-sectional correlations, Bret et al. (2002) found that 100m sprint running performance was significantly correlated with both leg strength and countermovement jump height, indicating the importance of both leg strength and power. Additionally, Hori et al. (2008) found that hang clean performance was significantly correlated with short distance sprint running ability.

Long-term trials: plyometrics

In respect of plyometrics, Sáez de Villarreal et al. (2012b) performed a meta-analysis assessing the effect of plyometric training. They concluded that plyometrics can improve sprint running performance but they are dose-responsive and the correct dose has a significantly better effect than too much or too little. In addition, they concluded that the choice of exercise is important and that adding resistance does not appear to improve performance gains.

Long-term trials: resisted sprinting

In a narrative review, Hrysomallis (2012) concluded that while resisted movement training in the form of sled towing and wearing weighted vests has been shown to increase sprint speed, it has not always been shown to be superior to unresisted forms of training. Clark et al. (2010) found that resisted sprint training and unresisted sprint training produced similar training effects in well-trained team sports athletes.

Acute trials: biomechanics

Introduction

Although there is no strong guidance from previous reviews in respect of which training modalities should be prioritized for sprint running, previous reviews investigating the importance of training transfer to sports performance (e.g. Young, 2006; and Randell et al. 2010) have concluded that exercises used in training should have some degree of biomechanical similarity to sports performance.

Biomechanical similarity: horizontal forces

The likely importance of horizontal forces during running indicate that horizontally-oriented resistance-training, power-based exercises or plyometrics may be useful for improving sprint running performance. This would indicate that measures of horizontal force or power and unilateral actions should both be better correlated with sprint running ability than vertical measures. Indeed, many studies have found that horizontal jumping performance is better correlated with sprint running ability than vertical jumping performance (e.g. Meylan et al. 2009, Maulder and Cronin, 2005; Habibi et al., 2010; Robbins, 2012; Robbins and Young, 2012).

Biomechanical similarity: unilateral training

Since sprint running involves unilateral leg movements, this may indicate that unilateral resistance training or unilateral plyometrics may be beneficial for preparing athletes in need of improving their high-speed running ability. Indeed, unilateral jumping appears to be better correlated with sprint running performance than bilateral jumping (e.g. Holm et al. 2008; McCurdy et al. 2010). Additionally, Ramírez-Campillo et al. (2015) found that when training youth soccer players with either unilateral or bilateral plyometrics exercises, the unilateral group increased 15m and 30m sprint speeds with much larger effect sizes than the bilateral group, although the difference between groups was not statistically significant.

Biomechanical similarity: muscle activity and joint moments

Since increasing running speed involves increasing net hip extension moments to a greater extent than either net knee or net ankle moments, this may suggest that exercises designed to develop the hip extensors may be most valuable for preparing athletes in need of superior sprint running ability. These findings are supported by research observations that increasing running speed involves increasing hamstrings and gluteus maximus muscle activity to a greater extent than the activity of other muscles. Based on this analysis it seems that developing the hamstrings and gluteus maximus muscles will provide the most favorable adaptations for improving sprint running speed.

Biomechanical similarity: force-velocity relationship

Since sprint running involves extremely high joint angular velocities and since it is very likely that muscle contraction velocity is a key limitation to maximum running speed, developing the ability to sprint must necessarily involve improving the ability to produce force quickly, which can be practiced using training methods involving explosive movements.

CONCLUSIONS REGARDING SPRINTING

There is currently a general consensus that no single training technique offers significantly greater benefits from any others and that a mixed approach is probably optimal.

Training methods that display biomechanical similarity to sprint running may be most beneficial. For example exercises involving horizontally-directed forces, unilateral exercises, exercises for the hamstrings and gluteus maximus, and training methods involving high-velocity force production.

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