Squat


The barbell squat is a key exercise in strength and conditioning programs. There are many barbell squat variations, which can be classified in different ways (including barbell placement, technique, stance width or foot placement, and fixed or free weight).

The test-re-test reliability of back squat 1RM testing is generally nearly perfect or very high, although a familiarization effect has been observed over subsequent sessions. In trained individuals, a difference of 4% can differentiate between individuals, and a difference of 8% can establish a real training effect. In untrained individuals, much larger differences may be necessary.

Based on changes in muscle activity with load, bar speed, and ROM, the prime movers in the back squat include the quadriceps, gluteus maximus and erector spinae. The hamstrings appear to function as antagonist co-contractors. The roles of the adductors, gastrocnemius and soleus and abdominals are unclear. During the back squat, using a wider stance and knee wraps increase gluteus maximus muscle activity, while using running shoes rather than no footwear increases quadriceps muscle activity. 

Most squat variations appear to lead to similar quadriceps, gluteus maximus and erector spinae muscle activity, but the back squat seems to display greater quadriceps muscle activity than either the split squat or overhead squat. No other exercise has been found to involve greater quadriceps muscle activity than the back squat but the barbell hip thrust involves greater gluteus maximus activity and the deadlift involves greater erector spinae muscle activity.

Heavier loads are lifted during partial rather than parallel squats, by individuals with greater levels of resistance-training experience, and by athletes using a powerlifting-style of squat compared to an Olympic weightlifting-style of squat. Ground reaction forces appear to be primarily a function of the absolute loads used.

The optimal load for power during back squats is unclear. Supportive equipment (knee wraps and weightlifting belts) appear to increase power output, most likely by increasing velocity as a result of stored elastic energy in the lowering phase. Greater rate of force development seems to be observed in the box squat than in other squat variations.

Greater trunk angles in the back squat are observed in subjects wearing no footwear rather than running shoes and when using cues to restrict the movement of the knees over the toes. The effect of cues to prevent knee movement over the toes on peak hip angle is unclear but cues to look downwards rather than upwards lead to more acute hip angles, while increasing fatigue leads to less acute peak hip angles.

Increasing load and wearing running shoes rather than no footwear appear to lead to more acute peak knee angles, while using cues to prevent forward knee movement over the toes and fatigue lead to less acute knee angles. Similarly, using weightlifting shoes and running shoes both lead to more acute peak ankle angles than using no footwear, while cues to prevent the knee from moving forward over the toes lead to less acute peak ankle angles.

Hip extensor moments in the back squat increase with increasing relative load, squat depth, trunk lean and with cues to prevent forward movement of the knees over the toes. They are greater using a powerlifting-style squat than a traditional squat. When using Smith machine squats, hip extensor moments are greater with a foot position that is further forward of the barbell or a backward body inclination.

In contrast, knee extensor moments in the back squat increase with increasing relative load and squat depth but reduce with cues to prevent forward movement of the knees over the toes or with greater trunk lean. They are greater using a traditional squat than when using a powerlifting-style squat but similar during back and front squats. When using Smith machine squats, knee extensor moments are greater with a foot position that is closer toward the barbell or a forward body inclination.

CONTENTS

Full table of contents

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

Background

Reliability of 1RM testing

Electromyography

External kinetics

Joint angle movements

Net joint moments

External moment arm lengths

References


BACKGROUND TO THE SQUAT

PURPOSE

This section provides some background to the squat exercise, its variations and how they are used, and suggests some reasons for its prominent position in strength and conditioning programs.

CONTRIBUTORS

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BACKGROUND

Introduction

The squat is a key exercise in strength and conditioning programs. There are many squat variations, which can be classified in various ways, including the placement of the barbell, the technique used, and whether they are performed with free weights or in a Smith machine. Primarily, squats are classified by the placement of the barbell. Squats classified in this way are described as back squats, front squats, and overhead squats and these variations are often viewed as completely distinct exercises. Secondarily, squats can be classified by the technique used in the type of strength sport that they resemble. Squats classified in this way are often described as Olympic squats or powerlifting squats and display certain key distinctive features. Thirdly, squats can be classified regarding whether they are performed using a free weight barbell or a barbell in a fixed apparatus, such as a Smith machine. Fourthly, squats can be classified by hip angles, which lead to different stance widths (wide, medium or narrow) and foot positions (neutral or outwardly rotated feet). Fifthly, squats can be classified according to whether there is a box placed at the bottom of the movement or whether they are performed freely without any box.

Squat variations

The back squat is the most commonly-performed squat variation in strength and conditioning programs. It is also a key element of most Olympic weightlifting training routines, and is contested as one of the three lifts that comprise the sport of powerlifting. The biomechanics of the back squat have been reviewed countless times over recent years (O’Shea, 1985; Chandler and Stone, 1991; Neitzel and Davies, 2000; Escamilla, 2001c; Schoenfeld, 2010; Clark et al. 2012), leading to a range of suggestions regarding performance, and various recommendations have been made for correct or optimal technique (Carter et al. 2013; Myer et al. 2014). The front squat is another very commonly-used squat in strength and conditioning programs and has a number of variations that are valuable for use in developing athletes (Larson et al. 1991; Cissik, 2000; Waller and Townsend, 2007; Bird and Casey, 2012).

THE REVIEW

Inclusion criteria

The main part of this page covers research into the biomechanics of the loaded barbell squat using the following inclusion criteria:

  • Study design = acute
  • Population = healthy adults
  • Intervention = loaded barbell squat
  • Comparator = squat variation or technique or other exercise
  • Outcome = biomechanical measure (muscle activity, kinetics, or kinematics)

Squat variations could include the back squat, front squat, overhead squat, Smith machine squat, box squat, and cambered bar squat. Squat techniques could include different styles (e.g. Olympic, powerlifting) or different hip angles (foot placements and stance widths). Other exercises could include any instance where the squat has been compared to another lower-body exercise, such as a leg press, lunge, or deadlift. Muscle activity studies were included where they used surface or fine wire electrodes to record electromyography (EMG). Outcomes recorded in studies of kinetics were reported for external load, ground reaction forces, power outputs, rate of force development, and net joint moments. Outcomes recorded in studies of kinematics were reported for peak trunk angles, and peak angles at the hip, knee and ankle.

Exclusion criteria

The main part of this page covers research into the biomechanics of the loaded barbell squat and excluded studies using the following exclusion criteria:

  • Study design = any non-acute study design
  • Population = any study not in healthy adults
  • Intervention = any study not using a loaded barbell squat
  • Comparator = any study not providing a comparator for the back squat
  • Outcome = any non-biomechanical measure

As a result of these exclusion criteria, this page does not cover the long-term effects of training using squats, either in relation to muscular adaptations (strength, hypertrophy, power and rate of force development) or in relation to the longitudinal transfer to sporting qualities (sprinting, jumping, throwing). It does not include research exploring squats of any kind in unhealthy or clinical populations. It does not cover research involving unloaded squats (also called “sit-to-stands”) or loaded squats performed without a barbell, either because they are loaded with dumbbells, elastic resistance, or boxes placed in the hands (also called “squat lifting”). It does not include any study where an aspect of the squat exercise was not explored in relation to another squat variation or another exercise and therefore excludes studies exploring the post-activation potentiation effect, which frequently makes use of the loaded barbell squat exercise.

Reporting of findings

Findings reported on this page are with very few exceptions provided only if the comparison met statistical significance (p < 0.05). Therefore, where it is noted that a study reported a finding, it is assumed that the finding was statistically significant. Where this is not the case, a note is always provided to clarify that the finding was only a trend and did not meet with the requirements of the tests used by the researchers to establish whether a finding was likely to be real or whether there was a risk of being fooled by randomness in the observation.

 

SECTION CONCLUSIONS

The squat is a key exercise in strength and conditioning programs. There are many squat variations, which can be classified in various ways, including the placement of the barbell, the technique used, and whether they are performed with free weights or in a Smith machine.


RELIABILITY OF 1RM TESTING

PURPOSE

This section details the test-re-test reliability of 1RM back squat testing, which helps provide strength and conditioning coaches with a method for assessing whether an improvement in 1RM back squat 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.

Types of reliability

Inter-rater reliability describes whether a test can be performed by different people at the same time and yet still produce the same (or at least a very similar) result. If two people score a subject or an outcome very differently while watching them perform the test at the same time, this would mean that the test had poor inter-rater reliability and this would challenge the overall assessment of the reliability of a test. Similarly, intra-rater reliability describes whether a test can be performed by the same person on two different occasions and yet still produce the same result. If the same person scores a subject or an outcome very differently on two different occasions, this would mean that the test had poor intra-rater reliability and this would challenge the overall assessment of the reliability of a test. Sometimes, true intra-rater can 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)
  • Large (r = 0.5 – 0.7)
  • Very large (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, rough 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).

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) (see Beckerman et al. 2001) or the Smallest Detectable Difference (SDD) (see Comfort and McMahon, 2014). 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). Whereas the SEM deals with differences between subjects, the MD addresses differences within the same subject. The MD is the difference that must be recorded between two test scores for the same subject when multiple measurements are taken, usually as the result of an intervention, in order for practitioners to be certain that a real change has actually taken place. 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 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).

RELIABILITY OF 1RM

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing the reliability of 1RM testing in the back squat exercise

Comparison – between sessions (test-re-test reliability)

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

Results 

The following relevant studies were identified that met the inclusion criteria: Soares-Caldeira (2009), Ritti-Dias (2011), Seo (2012), Augustsson (2013), Comfort (2014).

Findings

INTRA-CLASS CORRELATION COEFFICIENTS

The test-re-test reliability of 1RM back squat as measured by ICC has most often been reported as either nearly perfect (Soares-Caldeira et al. 2009, Ritti-Dias et al. 2011, Seo et al. 2012; Comfort and McMahon, 2014) or very large (Swinton et al. 2012, Augustsson and Svantesson, 2013). Lower reliability appears to be associated mainly with untrained individuals (Augustsson and Svantesson, 2013) while the highest levels of reliability appear to be observed in previously trained subjects (Soares-Caldeira, 2009; Comfort and McMahon, 2014). Additionally, there appears to be a training or familiarization effect, with later sessions tending to display higher values of 1RM than earlier sessions, even in moderately-trained individuals (Soares-Caldeira et al. 2009).

STANDARDIZED MEAN DIFFERENCE

The SEM for the 1RM back squat has been reported less frequently than the ICC but it can be estimated from data provided in the relevant studies. In trained individuals, the SEM appears to be between 1 – 4% (Soares-Caldeira et al. 2009; Ritti-Dias et al. 2011; Seo et al. 2012; Comfort and McMahon, 2014). In untrained individuals, it appears much higher at between 6 – 11% (Ritti-Dias et al. 2011; Augustsson and Svantesson, 2013). Therefore, the ability to differentiate 1RM back squat performances between individuals may depend substantially upon training status.

MINIMUM DIFFERENCE TO BE CONSIDERED REAL

The MD for the 1RM back squat has been reported less frequently than the ICC but it can be estimated from data provided in the relevant studies. In trained individuals, the MD appears to be between 2 – 8% (Soares-Caldeira et al. 2009; Seo et al. 2012; Comfort and McMahon, 2014). In completely untrained individuals, it appears much higher at between 17 – 30% (Ritti-Dias et al. 2011; Augustsson and Svantesson, 2013). Therefore, the ability to differentiate 1RM back squat performances for a given individual from the beginning of a training program to the end may only be feasible in trained individuals.

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SECTION CONCLUSIONS

The test-re-test reliability of back squat 1RM testing is generally either nearly perfect (r > 0.9) or very high (r = 0.7 – 0.9), with only a few reports identifying test-re-test reliability only as high (r = 0.5 – 0.7). This indicates that the 1RM back squat test is reliable, although a familiarization effect has been observed over subsequent sessions even in moderately trained individuals.

When measuring trained individuals, a difference of around 4% can differentiate between individuals, and a difference of 8% can establish a real training effect. However, when measuring untrained individuals, a difference of around 6 – 11% may be necessary to differentiate between individuals, and a difference of around 17 – 30% may be necessary to establish a real training effect.


 

ELECTROMYOGRAPHY (EMG)

PURPOSE

This section sets out a summary of the research that has explored the muscle activity of each of the main trunk and lower body muscles during the squat exercise, using electromyography (EMG).

GLUTEUS MAXIMUS

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing the muscle activity of the gluteus maximus during the squat exercise

Comparison – either normalized values relative to a maximum voluntary isometric contraction (MVIC) value or a dynamic reference contraction, or absolute values of voltage where such comparisons are appropriate

Outcome – percentage of MVIC

Results 

The following relevant studies were identified that met the inclusion criteria: McCaw (1999), Zink (2001), Caterisano (2002), Andersen (2006), Manabe (2007), Paoli (2009), Jones (2012), Li (2013), Aspe (2014), DeForest (2014), Gomes (2015), Yavuz (2015), Contreras (2015a), Contreras (2015b).

Findings

EFFECT OF TRAINING VARIABLES

Exploring training variables, Li et al. (2013), Aspe and Swinton (2014) and Gomes et al. (2015) all reported that greater relative loads produced greater levels of muscle activity. Manabe et al. (2007) reported that faster bar speeds produced greater muscle activity compared to slower bar speeds. Caterisano et al. (2002) reported that increasing depth led to increasing muscle activity (using the same absolute loads) but Contreras et al. (2015b) found that increasing depth had no effect on muscle activity (using the same relative loads), thereby indicating that so long as similar percentage of 1RM is used, depth has no effect on gluteus maximus muscle activity.

EFFECT OF EQUIPMENT

Exploring the effects of equipment on muscle activity, Zink et al. (2001) reported that a weightlifting belt did not affect muscle activity. However, Gomes et al. (2015) reported that knee wraps lead to increased muscle activity.

EFFECT OF HIP JOINT ANGLES

Comparing different stance widths, both McCaw and Melrose (1999) and Paoli et al. (2009) found that muscle activity was greater during squats with a wide stance width compared to those with a narrower stance width.

EFFECT OF EXERCISE VARIATION

Comparing back and front squats, both Contreras et al. (2015b) and Yavuz et al. (2015) found that front and back squats displayed equal levels of muscle activity (with the same relative loads). Similarly, comparing  the back squat and the split squat, both Jones et al. (2012) and DeForest et al. (2014) found no differences between conditions (with the same relative and adjusted absolute loads, respectively).

COMPARING THE BACK SQUAT TO OTHER EXERCISES

Comparing back squats with the leg press, Andersen et al. (2006) found that muscle activity was similar between the back squat and the horizontal leg press. However, Contreras et al. (2015) found that the barbell hip thrust displayed greater muscle activity than the barbell back squat.

Conclusions

Heavier loads, faster bar speeds, greater depth (with the same load), a wider stance, and using knee wraps all lead to increased gluteus maximus muscle activity during back squats. Back squats, front squats, split squats and leg presses all appear to lead to similar gluteus maximus muscle activity. However, the barbell hip thrust appears to lead to greater gluteus maximus activity than the barbell back squat.

QUADRICEPS

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing the muscle activity of the quadriceps during the squat exercise

Comparison – normalized values relative to a maximum voluntary isometric contraction (MVIC) value or a dynamic reference contraction, or absolute values of voltage where such comparisons are appropriate

Outcome – percentage of MVIC

Results 

The following relevant studies were identified that met the inclusion criteria: Signorile (1994), Stuart (1996), Wretenberg (1996), Ninos (1997), Escamilla (1998), McCaw (1999), Boyden (2000), Pick (2000), Zink (2001), Escamilla (2001b), Caterisano (2002), Anderson (2005), Andersen (2006), Manabe (2007), Schwanbeck (2009), Gullett (2009), Paoli (2009), McCurdy (2010), Pereira (2010), Jones (2012), Li (2013), Gorsuch (2013), Maddigan (2014), Aspe (2014), Luera (2014), Andersen (2014), Sinclair (2014), DeForest (2014), Gomes (2015), Yavuz (2015), Contreras (2015a), Contreras (2015b).

Findings

EFFECT OF INTRINSIC FEATURES

Both Wretenberg et al. (1996) and Pick and Becque (2000) found that stronger individuals displayed greater muscle activity than weaker individuals during the back squat. In the case of the data reported by Wretenberg et al. (1996), differences may also have arisen because of the styles of squat used by the stronger and weaker lifters, being powerlifters and Olympic weightlifters.

EFFECT OF TRAINING VARIABLES

Exploring the effects of training variables, McCaw and Melrose (1999), Li et al. (2013), Aspe and Swinton (2014) and Gomes et al. (2015) all reported that greater relative loads produced greater levels of muscle activity and Luera et al. (2014) showed that the correlation between increasing squat force and muscle activity was strong and linear. Manabe et al. (2007) reported that faster bar speeds produced greater muscle activity compared to slower bar speeds. Both Gorsuch et al. (2013) and Caterisano et al. (2002) reported that increasing depth led to increasing muscle activity (using the same relative and absolute loads, respectively). However, Contreras et al. (2015b) found that increasing depth had no effect on muscle activity (using the same relative loads), suggesting that so long as similar percentage of 1RM is used, depth is not important.

EFFECT OF EQUIPMENT

Exploring the effects of equipment on muscle activity, Zink et al. (2001) reported that a weightlifting belt did not affect muscle activity. However, Gomes et al (2015) reported effects of knee wraps that depended upon relative load but was not linear. Sinclair et al. (2014) compared the use of weightlifting shoes, minimalist footwear, running shoes, and no footwear (barefoot) and found that running shoes displayed greater muscle activity than no footwear but there were no other differences between conditions.

EFFECT OF HIP JOINT ANGLE

Comparing squats with different hip rotation angles, Ninos et al. (1997), Boyden et al. (2000) and Pereira et al. (2010) all found no differences in muscle activity between squats with the feet pointing neutrally forwards and with the feet turned out at 20 – 30 degrees (using the same absolute load). Similarly, McCaw and Melrose (1999), Escamilla et al. (2001b), and Paoli et al. (2009) all found no differences in muscle activity between narrow and wide stance width squats (using the same absolute load).

EFFECT OF EXERCISE VARIATION

Comparing front and back squats, neither Stuart et al. (1996), Gullett et al. (2009) or Contreras et al. (2015b) found any differences in muscle activity (with the same absolute or relative loads). However, Yavuz et al. (2015) found that front and back squats displayed equal levels of muscle activity for the vastus lateralis and rectus femoris but greater levels in the front squat for the vastus medialis (with the same relative loads). Comparing back and overhead squats, Aspe and Swinton (2014) found that muscle activity was greater in the back squat than in the overhead squat (with the same relative loads). Comparing free weight and machine squats, Anderson and Behm (2005) found that muscle activity was greater during the Smith machine squat than during a free weight squat (with the same absolute load), while Schwanbeck et al. (2009) found the opposite results, possibly because they used the same relative loads. Comparing the back squat and the split squat (with the same relative loads), both McCurdy et al. (2010) and Andersen et al. (2014) found that the back squat displayed greater muscle activity than the split squat. However, Jones et al. (2012) and DeForest et al. (2014) found no differences between exercises (with the same relative and adjusted absolute loads, respectively).

COMPARING THE SQUAT TO OTHER EXERCISES

Comparing the back squat with knee extensions, Signorile et al. (1994) found that muscle activity was greater during back squats than during knee extensions but Andersen et al. (2006) found the opposite results and Escamilla et al. (1998) found that muscle activity differences depended upon knee angle. Escamilla et al. (1998) reported that muscle activity was greater in the knee extension closer to full extension (15 – 65 degrees) and greater int the squat at greater angles of flexion (>83 degrees). Comparing the back squat with the forward lunge, Stuart et al. (1996) noted that the forward lunge displayed higher muscle activity than either the front or back squat (albeit using the same absolute load). Comparing the back squat with the leg press, Andersen et al. (2006) found that the leg press involved greater muscle activity than the back squat (with the same relative load) but Escamilla et al. (2001b) found the opposite results (also with the same relative load). Comparing the barbell hip thrust and the barbell back squat, Contreras et al. (2015) found no differences in muscle activity between exercises. Finally, Maddigan et al. (2014) compared a 10RM back squat with a 20 step maximum sled push and found no differences in muscle activity between the two exercises during the maximal tests.

Conclusions

Heavier loads, faster bar speeds, greater depth (with the same absolute and relative loads), and using running shoes rather than no footwear all lead to increased quadriceps muscle activity during back squats. Back squats, front squats, Smith machine squats, hip thrusts and sled pushes appear to display similar quadriceps muscle activity, but the back squat seems to display greater quadriceps muscle activity than either the split squat or overhead squat.

HAMSTRINGS

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing the muscle activity of the hamstrings during the squat exercise

Comparison – normalized values relative to a maximum voluntary isometric contraction (MVIC) value or a dynamic reference contraction, or absolute values of voltage where such comparisons are appropriate

Outcome – percentage of MVIC

Results 

The following relevant studies were identified that met the inclusion criteria: Stuart (1996), Ninos (1997), Escamilla (1998), McCaw (1999), Zink (2001), Escamilla (2001b), Caterisano (2002), Anderson (2005), Andersen (2006), Manabe (2007), Schwanbeck (2009), Paoli (2009), Gullett (2009), McCurdy (2010), Jones (2012), Li (2013), Gorsuch (2013), DeForest (2014), Luera (2014), Aspe (2014), Maddigan (2014), Andersen (2014), Sinclair (2014), Yavuz (2015), Contreras (2015a), Contreras (2015b).

Findings

EFFECT OF TRAINING VARIABLES

Exploring training variables, Aspe and Swinton (2014) reported that greater relative loads produced greater levels of muscle activity but Li et al. (2013) found that greater relative loads did not lead to greater increases in muscle activity. Additionally, Luera et al. (2014) showed that correlations between increasing squat force and muscle activity were only low-to-moderate. Manabe et al. (2007) reported that faster bar speeds produced greater muscle activity compared to slower bar speeds. Caterisano et al. (2002) reported that increasing depth led to increasing muscle activity (using the same absolute loads) but both Gorsuch et al. (2013) and Contreras et al. (2015b) reported that increasing depth had no effect on muscle activity (using the same relative loads).

EFFECT OF EQUIPMENT

Exploring the effect of supportive equipment, Zink et al. (2001) reported that a weightlifting belt did not affect muscle activity. Sinclair et al. (2014) compared the use of weightlifting shoes, minimalist footwear, running shoes, and no footwear (barefoot) and found no differences between conditions.

EFFECT OF HIP JOINT ANGLES

Comparing squats with different hip rotation angles, Ninos et al. (1997) found no differences in muscle activity between squats with the feet pointing neutrally forwards and the feet turned out at 30 degrees (using the same absolute load). Similarly, McCaw and Melrose (1999), Escamilla et al. (2001b) and Paoli et al. (2009) all found no differences in muscle activity between narrow and wide stance width squats (using the same absolute load).

EFFECT OF EXERCISE VARIATION

Comparing front and back squats, Stuart et al. (1996), Gullett et al. (2009), Yavuz et al. (2015) and Contreras et al. (2015b) all found no differences in muscle activity between front and back squats (with the same absolute or relative loads). Comparing back and overhead squats, Aspe and Swinton (2014) found that muscle activity was greater in the back squat than in the overhead squat (with the same relative loads). Comparing free weight and machine squats, Anderson and Behm (2005) found no differences in muscle activity between the  free weight and Smith machine squat (using the same absolute loads), while Schwanbeck et al. (2009) reported that the free weight back squat displayed higher muscle activity than a Smith machine squat, possibly because they used the same relative loads. Comparing the back squat and the split squat (with the same relative loads), both McCurdy et al. (2010) and Andersen et al. (2014) found that the split squat displayed greater muscle activity than the back squat. DeForest et al. (2014) also found greater muscle activity in the split squat, using the same adjusted absolute loads. However, Jones et al. (2012) found no differences between exercises.

COMPARING THE SQUAT TO OTHER EXERCISES

Comparing the back squat and the forward lunge, Stuart et al. (1996) noted that the forward lunge displayed lower muscle activity than either the front or back squat. Comparing the back squat and leg press, Andersen et al. (2006) found that the leg press involved similar muscle activity to the back squat (with the same relative load) but both Escamilla et al. (1998) and Escamilla et al. (2001b) found that the squat was superior to the leg press (also with the same relative load). Comparing the barbell back squat and the barbell hip thrust, Contreras et al. (2015) found that the hip thrust displayed greater muscle activity. Finally, Maddigan et al. (2014) compared a 10RM back squat with a 20 step maximum sled push and found no differences in muscle activity between the two exercises during the maximal tests.

Conclusions

Faster bar speeds and greater depth with the same absolute loads (but not the same relative loads), lead to increased hamstrings muscle activity during back squats. The back squat appears to display greater hamstrings muscle activity than the forward lunge and overhead squat but less hamstrings muscle activity than the split squat and hip thrust. There is no difference in hamstrings muscle activity between back and front squats.

ADDUCTORS

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing the muscle activity of the adductors (adductor group, adductor magnus, or adductor longus) during the squat exercise

Comparison – normalized values relative to a maximum voluntary isometric contraction (MVIC) value or a dynamic reference contraction, or absolute values of voltage where such comparisons are appropriate

Outcome – percentage of MVIC

Results 

The following relevant studies were identified that met the inclusion criteria: McCaw (1999), Zink (2001), Paoli (2009), Pereira (2010).

Findings

EFFECT OF TRAINING VARIABLES

Comparing squats with different relative loads, McCaw and Melrose (1999) found that adductor longus muscle activity was greater when using heavier relative loads than when using lighter relative loads.

EFFECT OF EQUIPMENT

Exploring the effect of supportive equipment, Zink et al. (2001) reported that a weightlifting belt did not affect muscle activity.

EFFECT OF HIP JOINT ANGLES

Comparing squats with different stance widths, both McCaw and Melrose (1999) and Paoli et al. (2009) found that stance width had no effect on the muscle activity of the adductors (using the same absolute load). In contrast, Pereira et al. (2010) found that hip adductor muscle activity was increased by increasing hip external rotation angle (between 0 and 30 degrees), when using the same absolute load for each variation. However, they found that there was no further increase between 30 and 50 degrees, suggesting that there is an optimal length-tension relationship before this point is reached.

Conclusions

Heavier loads appear to lead to increased hip adductor muscle activity during back squats. Although stance width appears to have no effect, greater hip external rotation angles (up to 30 degrees) appear to cause increased hip adductor muscle activity.

GASTROCNEMIUS AND SOLEUS

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing the muscle activity of the gastrocnemius or soleus during the squat exercise

Comparison – normalized values relative to a maximum voluntary isometric contraction (MVIC) value or a dynamic reference contraction, or absolute values of voltage where such comparisons are appropriate

Outcome – percentage of MVIC

Results 

The following relevant studies were identified that met the inclusion criteria: Escamilla (2001b), Anderson (2005), Manabe (2007), Paoli (2009), Schwanbeck (2009), Li (2013), Gorsuch (2013), DeForest (2014), Sinclair (2014), Aspe (2014), Andersen (2014), Maddigan (2014).

Findings

EFFECT OF TRAINING VARIABLES

Both Li et al. (2013) and Aspe and Swinton (2014) reported that greater relative loads produced greater levels of muscle activity. Manabe et al. (2007) reported that faster bar speeds did not cause greater muscle activity compared to slower bar speeds. Gorsuch et al. (2013) found that squat depth had no effect on muscle activity (using the same relative loads).

EFFECT OF EQUIPMENT

Comparing different types of footwear, Sinclair et al. (2014) compared the use of weightlifting shoes, minimalist footwear, running shoes, and no footwear (barefoot) and found no differences between conditions.

EFFECT OF HIP JOINT ANGLES

Comparing squats with different stance widths, Escamilla et al. (2001b) found that muscle activity was greater in narrow stance width squats compared to wide stance width squats.

EFFECT OF EXERCISE VARIATION

Comparing the back and overhead squats, Aspe and Swinton (2014) found that muscle activity was greater in the back squat than in the overhead squat (with the same relative loads). Comparing free weight and machine squats, Anderson and Behm (2005) found no differences between conditions (with the same absolute loads) but Schwanbeck et al. (2009) noted that the free weight back squat displayed higher muscle activity than a Smith machine squat (with the same relative loads). Comparing the back squat and the split squat, DeForest et al. (2014) found no differences between exercise variations (using the same adjusted absolute loads).

COMPARING THE SQUAT WITH OTHER EXERCISES

Comparing the back squat and the leg press, Escamilla et al. (2001b) found that there was no difference in muscle activity between the squat and the leg press. Comparing the back squat and sled push, Maddigan et al. (2014) compared a 10RM back squat with a 20 step maximum sled push and found that the sled displayed superior muscle activity to the squat during the maximal tests.

Conclusions

Heavier loads and narrower stance widths appear to lead to increased gastrocnemius and soleus muscle activity during back squats. The back squat appears to display similar gastrocnemius and soleus muscle activity to the leg press but less than the sled push.

ERECTOR SPINAE

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing the muscle activity of the erector spinae during the squat exercise

Comparison – normalized values relative to a maximum voluntary isometric contraction (MVIC) value or a dynamic reference contraction, or absolute values of voltage where such comparisons are appropriate

Outcome – percentage of MVIC

Results 

The following relevant studies were identified that met the inclusion criteria: Zink (2001), Anderson (2005), Hamlyn (2007), Manabe (2007), Nuzzo (2008), Paoli (2009), Willardson (2009), Bressel (2009), Gullett (2009), Schwanbeck (2009), Comfort (2011), Jones (2012), Li (2013), Gorsuch (2013), Sinclair (2014), Fletcher (2014), Aspe (2014), Maddigan (2014), Andersen (2014), Yavuz (2015).

Findings

EFFECT OF TRAINING VARIABLES

Exploring the effects of training variables, Bressel et al. (2009), Willardson et al. (2009), Li et al. (2013) and Aspe and Swinton (2014) all reported that greater relative loads produced greater levels of muscle activity. Manabe et al. (2007) reported that faster bar speeds produced greater muscle activity compared to slower bar speeds. Gorsuch et al. (2013) found that muscle activity increased with increasing squat depth (using the same relative loads).

EFFECT OF EQUIPMENT

Exploring the effect of supportive equipment, Zink et al. (2001) reported that a weightlifting belt did not affect muscle activity. Sinclair et al. (2014) compared the use of weightlifting shoes, minimalist footwear, running shoes, and no footwear (barefoot) and found no differences between conditions.

EFFECT OF EXERCISE CUES

Assessing the effects of cues, Bressel et al. (2009) found that conscious efforts to contract the abdominal muscles during squats did not affect the muscle activity of the erector spinae.

EFFECT OF EXERCISE VARIATION

Comparing front and back squats, Comfort et al. (2011) reported greater muscle activity in the front squat than in the back squat (using the same absolute load) but Gullett et al. (2009) and Yavuz et al. (2015) found no differences between front and back squats when using the same relative load. Comparing back and overhead squats, Aspe and Swinton (2014) found that muscle activity was greater in the back squat than in the overhead squat (with the same relative loads). Comparing free weight and machine squats, while some researchers have reported lower erector spinae muscle activity in the Smith machine squat than in the free weight back squat, with both the same absolute (Anderson and Behm, 2005) and relative (Fletcher and Bagley, 2014) loads, Schwanbeck et al. (2009) found no differences (using the same relative loads). Comparing the back squat with the split squat (with the same relative loads), both Jones et al. (2012) and Andersen et al. (2014) found no differences in muscle activity between exercises.

COMPARING THE SQUAT WITH OTHER EXERCISES

Although Willardson et al. (2009) found that muscle activity was greater in the deadlift than in the back squat, these results may depend upon the exact region measured, as Hamlyn et al. (2007) reported greater muscle activity in the back squat than the deadlift in the lower erectors but greater muscle activity in the deadlift than the back squat in the upper erectors (with the same relative loads), although Nuzzo et al. (2008) reported no differences (also using the same relative loads). Additionally, while Comfort et al. (2011) found that muscle activity was greater in the superman exercise than in the back squat, this involved a low absolute load and therefore it is unsurprising that Hamlyn et al. (2007) reported greater muscle activity in the back squat than in the superman when using a heavy relative load (80% of 1RM). Finally, comparing the back squat and sled push, Maddigan et al. (2014) compared a 10RM back squat with a 20 step maximum sled push and found that the squat displayed superior muscle activity to the sled during the maximal tests.

Conclusions

Heavier loads, faster bar speeds, and greater depth (with the same relative load), all lead to increased erector spinae muscle activity during back squats.  The back squat displays greater erector spinae muscle activity than the overhead squat, superman or sled push exercises but less than the deadlift.

ABDOMINALS

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing the muscle activity of the abdominal musculature (including rectus abdominis, internal or external obliques, or transverse abdominis) during the squat exercise

Comparison – normalized values relative to a maximum voluntary isometric contraction (MVIC) value or a dynamic reference contraction, or absolute values of voltage where such comparisons are appropriate

Outcome – percentage of MVIC

Results 

The following relevant studies were identified that met the inclusion criteria: Anderson (2005), Hamlyn (2007), Nuzzo (2008), Willardson (2009), Bressel (2009), Schwanbeck (2009), Comfort (2011), Aspe (2014), Andersen (2014), Maddigan (2014).

Findings

EFFECT OF TRAINING VARIABLES

Both Willardson et al. (2009) and Aspe and Swinton (2014) reported that greater relative loads produced greater levels of muscle activity.

EFFECT OF EXERCISE CUES

Assessing the effects of cues, Bressel et al. (2009) found that conscious efforts to contract the abdominal muscles during squats caused increased muscle activity.

EFFECT OF EXERCISE VARIATION

Comparing front and back squats, Comfort et al. (2011) found no differences in muscle activity. Comparing back and overhead squats, Aspe and Swinton (2014) found that muscle activity was greater in the overhead squat than in the back squat (with the same relative loads). Comparing free weight and machine squats, Anderson and Behm (2005) and Schwanbeck et al. (2009) found no differences between the free weight back squat and the Smith machine squat, with either the same relative or absolute loads. Comparing the back squat and the split squat, Andersen et al. (2014) found that the split squat displayed greater external oblique muscle activity but similar rectus abdominis muscle activity to the back squat.

COMPARING THE SQUAT WITH OTHER EXERCISES

Comparing the back squat and deadlift, Hamlyn et al. (2007), Nuzzo et al. (2008) and Willardson et al. (2009) all found no differences in muscle activity between the deadlift and the back squat. Comparing the back squat and standard core exercises, Comfort et al. (2011) reported that the plank exercise produced much greater muscle activity than either the front or back squat variations but Nuzzo et al. (2008) found no differences in muscle activity between the back squat and three different Swiss ball stability exercises. Finally, comparing the back squat and sled push, Maddigan et al. (2014) compared a 10RM back squat with a 20 step maximum sled push and found no differences in muscle activity between the two exercises during the maximal tests.

Conclusions

Heavier loads, and conscious cues to contract the abdominals lead to increased abdominal muscle activity during back squats.  The back squat appears to display lower abdominal muscle activity than the overhead squat or plank exercises but similar abdominal muscle activity to the front squat and deadlift.

SECTION CONCLUSIONS

Based on changes in muscle activity with load, bar speed, and ROM, the prime movers in the back squat include the quadriceps, gluteus maximus and erector spinae. The hamstrings appear to function as antagonist co-contractors. The roles of the adductors, gastrocnemius and soleus and abdominals are unclear. During the back squat, using a wider stance and knee wraps increase gluteus maximus muscle activity, while using running shoes rather than no footwear increases quadriceps muscle activity.

Most squat variations appear to lead to similar quadriceps, gluteus maximus and erector spinae muscle activity, but the back squat seems to display greater quadriceps muscle activity than either the split squat or overhead squat. No other exercise has been found to involve greater quadriceps muscle activity than the back squat but the barbell hip thrust involves greater gluteus maximus activity and the deadlift involves greater erector spinae muscle activity.


EXTERNAL KINETICS

PURPOSE

This section sets out a summary of the research that has explored the external kinetics (ground reaction forces, power outputs, and rate of force development) during the squat exercise.

EXTERNAL LOADING (1RM)

Selection criteria

Population – any healthy, adult population

Intervention – any acute study measuring the effect of condition on 1RM during the squat exercise, with >2 different conditions

Comparison – between squat variations

Outcome – 1RM

Results 

The following relevant studies were identified that met the inclusion criteria: Wretenberg (1996), Ritti-Dias (2011), Cotter (2013), Gorsuch (2013),  Pallarés (2014), Yavuz (2015).

Findings

EFFECT OF INTRINSIC FEATURES

Assessing the 1RM back squat in individuals with different levels of training experience, Ritti-Dias et al. (2011) found that subjects with greater resistance-training experience displayed greater back squat 1RM than subjects with less resistance-training experience.

EFFECT OF TRAINING VARIABLES

Assessing the effect of squat depth, Cotter et al. (2013) compared the effect of squat depth on 1RM achieved and found that 1RM increased substantially in the order above parallel > parallel > below parallel. Similarly, Gorsuch et al. (2013) reported that the absolute load was greater during squats to above parallel than during squats to parallel, when using the same relative loads. Surprisingly, Pallarés et al. (2014) found that incorporating a pause into the 1RM test did not alter the measured 1RM, although there was a large albeit non-significant trend for the paused squat 1RM to be lighter than the touch-and-go 1RM, which may therefore be type II error (90.3 ± 14.7 vs. 97.2 ± 16.8kg).

EFFECT OF EXERCISE VARIATION

Comparing the Olympic and powerlifting squats, Wretenberg et al. (1996) found that powerlifters performing the powerlifting squat lifted heavier loads that Olympic weightlifters using the Olympic-style back squat. Comparing the back and front squats, Yavuz et al. (2015) found that loads were greater in the back squat than in the front squat.

Conclusions

Heavier absolute loads are lifted by individuals with greater levels of resistance-training experience, as well as athletes using a powerlifting-style of squat compared to an Olympic weightlifting-style of squat. Substantially heavier absolute loads are required to achieve the same relative loads when using partial squats as for parallel squats.

GROUND REACTION FORCES

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing ground reaction forces during the squat exercise

Comparison – between squat variations or between legs

Outcome – ground reaction forces in the lifting phase

Results 

The following relevant studies were identified that met the inclusion criteria: Lander (1986), Escamilla (2001b), Kellis (2005), Zink (2006), Flanagan (2007), McBride (2010), Blatnik (2012), Drinkwater (2012), Swinton (2012), Okkonen (2013), Aspe (2014).

Findings

EFFECT OF INTRINSIC FEATURES

Comparing forces exerted by each leg, Flanagan and Salem (2007) reported ground reaction forces on the left side were slightly greater (by around 6%) than the right side, irrespective of loading condition.

EFFECT OF TRAINING VARIABLES

Exploring training variables, Kellis et al. (2005), Zink et al. (2006) and Drinkwater et al. (2012) all found that increasing relative load led to increased ground reaction forces. Additionally, Drinkwater et al. (2012) also found that partial depth squats produced greater ground reaction forces than full range-of-motion squats, which was likely a function of the larger absolute loads used.

EFFECT OF EQUIPMENT

Assessing the effects of supportive gear, Blatnik et al. (2012) found that wearing a squat suit had no effect on ground reaction forces at a range of loads (80% – 100% of 1RM).

EFFECT OF HIP JOINT ANGLES

Comparing squats with different stance widths, Escamilla et al. (2001b) found no differences in ground reaction forces between squats with wide and narrow stances (with the same absolute loads).

EFFECT OF EXERCISE VARIATION

Comparing the box squat and back squat, McBride et al. (2010) reported that the box squat displayed greater ground reaction forces than the traditional squat with 70% of 1RM (but not 60% or 80% of 1RM), when using the same absolute load. In contrast, Swinton et al. (2012) found that peak ground reaction forces were greater during the traditional and powerlifting squat variations than during the box squat variation (using the same relative load) but there was no difference between traditional and powerlifting squat variations. Comparing the back and overhead squats, Aspe and Swinton (2014) found that the back squat displayed greater ground reaction forces to the overhead squat with the same relative load but similar ground reaction forces when using the same absolute load. Comparing back squats and squats with a cambered bar, Lander et al. (1986) found no differences in ground reaction forces (with the same relative loads).

COMPARING THE SQUAT TO OTHER EXERCISES

Comparing the back squat with sled pulling, Okkonen and Häkkinen (2013) reported that peak ground reaction forces with 70% of half squat 1RM were greater than during either block starts or sled pulling with loads of 10% or 20% of bodyweight.

Conclusions

Ground reaction forces appear to be primarily if not exclusively a function of the absolute loads used and do not appear to be markedly affected by other parameters.

POWER OUTPUTS

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing system power outputs during the squat exercise

Comparison – between squat variations

Outcome – system power output in the lifting phase

Results 

The following relevant studies were identified that met the inclusion criteria: Siegel (2002), Zink (2006), McBride (2010), Drinkwater (2012), Lake (2012), Blatnik (2012), Swinton (2012).

Findings

EFFECT OF TRAINING VARIABLES

Various contrasting findings have been reported for the effect of relative load on power output in the squat. Siegel et al. (2002) originally found that peak power output occurred between 50 – 70% of 1RM for the squat. In contrast, Drinkwater et al. (2012) found that increasing relative load (from 67% to 83% of 1RM) led to increased power output. However, Zink et al. (2006) did not find any effect of relative load on power output, most likely because they observed considerable inter-individual variability in respect of the relative load at which maximum power output was observed. In terms of other training variables, Drinkwater et al. (2012) found that partial depth squats produced greater power output than full range-of-motion squats.

EFFECT OF EQUIPMENT

Assessing the effects of supportive gear, Blatnik et al. (2012) found that wearing a squat suit increased power output at several different relative loads (80% – 90% of 1RM) compared to not wearing a squat suit. Lake et al. (2012) similarly found that wearing knee wraps improved peak power (when using 80% of 1RM).

EFFECT OF EXERCISE VARIATION

Comparing the back squat and box squat, McBride et al. (2010) reported that the box squat displayed greater power outputs than the traditional squat with 80% of 1RM (but not 70% or 80% of 1RM), when using the same absolute loads. In contrast, Swinton et al. (2012) found that system power outputs were greater during the traditional and powerlifting squat variations than during the box squat variation but there was no difference between traditional and powerlifting squat variations (with the same relative loads).

Conclusions

Power outputs during back squats differ from jump squats and the optimal load for power is unclear. Substantial inter-individual variability appears to exist in respect of the load at which power is greatest. Supportive equipment (knee wraps and weightlifting belts) appear to increase power output, most likely by increasing velocity as a result of stored elastic energy in the lowering phase.

RATE OF FORCE DEVELOPMENT

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing rate of force development during the squat exercise

Comparison – between squat variations

Outcome – rate of force development in the lifting phase

Results 

The following relevant studies were identified that met the inclusion criteria: Swinton (2012).

Findings

EFFECT OF EXERCISE VARIATION

Comparing the back squat and box squat, Swinton et al. (2012) found that rate of force development was 3 – 4 times greater during the box squat variation than during the traditional and powerlifting squat variations. However, there was no difference between traditional and powerlifting squat variations.

Conclusions

Greater rate of force development seems to be observed in the box squat than in other squat variations. The reasons for this are unclear but may relate to the pause before commencing the lifting phase. Whether this acute difference could translate to long-term improvements is unclear.

SECTION CONCLUSIONS

Heavier loads are lifted during partial rather than parallel squats, by individuals with greater levels of resistance-training experience, and by athletes using a powerlifting-style of squat compared to an Olympic weightlifting-style of squat. Ground reaction forces appear to be primarily a function of the absolute loads used.

The optimal load for power during back squats is unclear. Supportive equipment (knee wraps and weightlifting belts) appear to increase power output, most likely by increasing velocity as a result of stored elastic energy in the lowering phase. Greater rate of force development seems to be observed in the box squat than in other squat variations.


JOINT ANGLE MOVEMENTS

PURPOSE

This section sets out a summary of the research that has explored the joint angle movements during the squat exercise, using motion analysis software in either two dimensions (2D) or three dimensions (3D).

BACKGROUND

Kinematics reported in studies are not always easy to interpret. There are two main types of angle: absolute angles and relative angles. Absolute angles are those that represent the angles of the trunk, thigh or shank relative to the horizontal. Relative angles are those that represent the angles of the hip, knee and ankle relative to the body. The following diagram shows a representation of the squat in the bottom position performed with a medium width stance by masters powerlifters, with the joint angle data taken from Escamilla et al. (2001a) and the segment length data taken from Zatsiorsky et al. as reported in De Leva (1996).

Squat

PEAK TRUNK ANGLES

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing peak trunk angles in the sagittal plane during the squat exercise

Comparison – between squat variations or lifters of differing expertise

Outcome – peak joint angles (more acute angles are more “closed” while less acute angles are more “open”)

Results 

The following relevant studies were identified that met the inclusion criteria: Lander (1986), Russell (1989), Orloff (1997), Zink (2001), Escamilla (2001a), Fry (2003), Donnelly (2006), Hirata (2007), Gullet (2009), Gutierrez (2009), McCurdy (2010), Diggin (2011), Swinton (2012), List (2013), Sato (2013), Sinclair (2014).

Findings

EFFECT OF INTRINSIC FEATURES

Orloff et al. (1997) assessed the effect of training status on peak trunk angle (using the same absolute loads). They found that trained individuals remained more upright and therefore displayed a less acute peak trunk angle than untrained subjects.

EFFECT OF TRAINING VARIABLES

Orloff et al. (1997) assessed the effect of load on peak trunk angle and found that there was no effect with increasing load. List et al. (2013) found that load had a complex effect on peak lumbar and thoracic angles. Peak lumbar angle was found to reduce with increasing load from no load through to 50% of bodyweight, which represents a straightening of the spine under load. In contrast, peak thoracic angle first increased from no load to 25% of bodyweight and then decreased from 25% of bodyweight to 50% of bodyweight.

EFFECT OF EQUIPMENT

Exploring the effects of supportive gear, Zink et al. (2001) found no effect on peak trunk angle of using a weightlifting belt. Sinclair et al. (2014) compared the use of weightlifting shoes, minimalist footwear, running shoes, and no footwear (barefoot) and found no differences between conditions. However, Sato et al. (2013) found that no footwear allowed greater trunk lean than wearing running shoes.

EFFECT OF EXERCISE CUES

Taking the trunk as a single segment, Donnelly et al. (2006) found that peak trunk angle was similar whether lifters were cued to look downwards or upwards; both Fry et al. (2003) and Hirata and Duarte (2007) found that when artificially restricting forward knee motion, this produced greater forward lean and hence a more acute peak trunk angle. Taking the trunk as multiple segments, List et al. (2013) found that peak thoracic trunk angle was greater when artificially restricting forward knee motion using visual cues compared to unrestricted squats, and peak lumbar trunk angle displayed a non-significant trend in the same direction.

EFFECT OF HIP JOINT ANGLES

Comparing the effects of squats with different stance widths, Escamilla et al. (2001a) compared narrow, medium and wide stance back squats and found that peak trunk angles did not differ between variations.

EFFECT OF EXERCISE VARIATION

Both Russell and Phillips (1989) and Diggin et al. (2011) reported that peak trunk angle was more acute during the back squat than during the front squat (performed to a standardized depth). McCurdy et al. (2010) reported that peak trunk angle was more acute during the back squat than during a rear-foot elevated split squat. Swinton et al. (2012) found that peak trunk angle was similar in the traditional and powerlifting squat variations but was much less acute during the box squat. Lander et al. (1986) found no difference in trunk angles between back squats and squats using a cambered bar. Finally, Gutierrez and Bahamonde (2009) found that peak trunk angle was more acute during a free weight back squat compared to a Smith machine squat.

Conclusions

Greater trunk angles in the back squat are observed in untrained individuals, in subjects wearing no shoes, and when using cues to restrict the forward movement of the knees over the toes. Greater trunk angles are also observed during the back squat compared to the front squat, box squat, Smith machine squat, and split squat.

PEAK HIP JOINT ANGLES

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing peak hip angles in the sagittal plane during the squat exercise

Comparison – between squat variations, between legs, or between lifters of differing expertise

Outcome – peak joint angles (more acute angles are more “closed” while less acute angles are more “open”)

Results 

The following relevant studies were identified that met the inclusion criteria: Wretenberg (1996), Zink (2001), Escamilla (2001a), Fry (2003), Kellis (2005), Donnelly (2006), Flanagan (2007), Manabe (2007), Braidot (2007), Hales (2009), Gutierrez (2009), Lorenzetti (2010), McKean (2010), Swinton (2012), List (2013), Sinclair (2014), Hooper (2014), Gomes (2015), Yavuz (2015).

Findings

EFFECT OF INTRINSIC FEATURES

Comparing differences between legs during the back squat, Flanagan and Salem (2007) reported that peak hip angles did not differ between legs and thus there were no bilateral differences. Hooper et al. (2014) found that greater levels of fatigue led to less acute hip angles.

EFFECT OF TRAINING VARIABLES

Exploring the effects of training variables, Kellis et al. (2005) found that joint angles differed between relative loads but did not identify how the individual hip, knee and ankle joints differed; however, McKean et al. (2010) reported that peak hip angle was more acute with load compared to no load, while both List et al. (2013) and Gomes et al. (2015) reported that peak hip angle became less acute with heavier relative loads. Manabe et al. (2007) found that there was no difference in peak hip angles between squats performed at slow, moderate or fast speeds.

EFFECT OF EQUIPMENT

Exploring the effects of supportive gear, Gomes et al. (2015) noted that knee wraps had no effect on peak hip angles. Similarly, Zink et al. (2001) found no effect on peak hip angle of using a weightlifting belt. Sinclair et al. (2014) compared the use of weightlifting shoes, minimalist footwear, running shoes, and no footwear (barefoot) and found no differences between conditions.

EFFECT OF EXERCISE CUES

Exploring the effects of movement cues, Lorenzetti et al. (2010) found that peak hip angle was more acute when lifters were visibly cued to prevent the knee from moving forward over the toes, compared to when they were allowed to lift normally. However, using a similar technique, List et al. (2013) found that there was no difference in peak hip angle between restricted and unrestricted squats and while Fry et al. (2003) found that artificially restricting forward knee motion produced greater forward trunk lean, this did not also lead to a difference in peak hip angle. Finally, Donnelly et al. (2006) found that peak hip angle was more acute when lifters were cued to look downwards rather than upwards.

EFFECT OF HIP JOINT ANGLES

Comparing the effects of squats with different stance widths, Escamilla et al. (2001a) found that peak hip angles did not differ between narrow, medium and wide stance width back squat variations.

EFFECT OF EXERCISE VARIATION

Both Braidot et al. (2007) and Yavuz et al. (2015) found that peak hip angle was more acute during the back squat than during the front squat. Wretenberg et al. (1996) found that peak hip angle was less acute in the Olympic weightlifting-style squat than in the powerlifting squat. Swinton et al. (2012) found that the peak hip angle was less acute in the traditional squat than in the powerlifting squat variation but there was no difference between either of these variations and the box squat. Finally, Gutierrez and Bahamonde (2009) found that peak hip angle was more acute during a free weight back squat compared to a Smith machine squat.

COMPARISON WITH OTHER EXERCISES

Comparing the back squat with other exercises, Hales et al. (2009) compared the peak hip angles in the back squat and deadlift. They reported that the squat displayed a more acute peak hip angle than the deadlift, when performed under powerlifting regulations.

Conclusions

The effects of load and cues to prevent forward knee movement over the toes on peak hip angle are unclear. However, cues to look downwards rather than upwards lead to more acute hip angles, while increasing fatigue leads to less acute hip angles. Peak hip angle is more acute during the back squat than the front squat, Smith machine squat or deadlift.

PEAK KNEE JOINT ANGLES

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing peak knee angles in the sagittal plane during the squat exercise

Comparison – between squat variations, between legs, or between lifters of differing expertise

Outcome – peak joint angles (more acute angles are more “closed” while less acute angles are more “open”)

Results 

The following relevant studies were identified that met the inclusion criteria: Lander (1986), Russell (1989), Wretenberg (1996), Zink (2001), Escamilla (2001a), Fry (2003), Kellis (2005), Donnelly (2006), Hirata (2007), Braidot (2007), Manabe (2007), Flanagan (2007), Hales (2009), Miletello (2009), Gutierrez (2009), Lorenzetti (2010), McKean (2010), Diggin (2011), Swinton (2012), List (2013), Sato (2013), Hooper (2014), Sinclair (2014), Gomes (2015), Yavuz (2015).

Findings

EFFECT OF INTRINSIC FEATURES

Comparing differences between legs during the back squat, Flanagan and Salem (2007) found that peak knee flexion angles displayed bilateral differences, with the right side achieving a more acute angle than the left side. Hooper et al. (2014) found that greater levels of fatigue led to less acute knee angles. Miletello et al. (2009) analysed the peak knee angles between lifters of different experience levels and found that novice lifters achieved the most acute peak knee angles, followed by college-level lifters, and finally high-school lifters.

EFFECT OF TRAINING VARIABLES

Exploring the effects of training variables, Kellis et al. (2005) found that peak joint angles differed between relative loads but did not identify how the individual hip, knee and ankle joints differed; however, both McKean et al. (2010) and List et al. (2013) reported that peak knee angle became more acute with load compared to no load or with increasing load (from 25% to 50% of bodyweight), while Gomes et al. (2015) reported that peak knee angle was similar with heavy and moderate relative loads; Manabe et al. (2007) found that there was no difference in peak knee angles between squats performed at slow, moderate or fast speeds.

EFFECT OF EQUIPMENT

Exploring the effects of supportive gear, Zink et al. (2001) found no effect on peak knee angle of using a weightlifting belt. Sinclair et al. (2014) compared the use of weightlifting shoes, minimalist footwear, running shoes, and no footwear (barefoot) and found that running shoes displayed greater peak knee flexion angles than no footwear but there were no other differences between conditions. Similarly, Sato et al. (2013) also found that running shoes displayed greater peak knee flexion angles than no footwear.

EFFECT OF EXERCISE CUES

Assessing the effects of cues, Fry et al. (2003), Hirata and Duarte (2007), Lorenzetti et al. (2010) and List et al. (2013) all found that peak knee angles were less acute when lifters were visibly or forcibly cued to prevent the knee from moving forward over the toes, compared to when they were allowed to lift normally; while Donnelly et al. (2006) found that peak knee angle was similar whether lifters were cued to look downwards or upwards.

EFFECT OF HIP JOINT ANGLES

Comparing the effects of squats with different stance widths, Escamilla et al. (2001a) compared narrow, medium and wide stance back squats and found that peak knee angles did not differ between variations.

EFFECT OF EXERCISE VARIATION

Comparing squat variations, Russell and Phillips (1989), Braidot et al. (2007), Diggin et al. (2011) and Yavuz et al. (2015) all reported that peak knee angles were similar during the back squat and front squat, even when each variation was performed to a standardized depth. Wretenberg et al. (1996) found that peak knee angle was more acute in the Olympic weightlifting-style squat than in the powerlifting squat. Swinton et al. (2012) found that peak knee angles were more acute in the order traditional > powerlifting > box squat variations. Lander et al. (1986) found no difference in knee angles between back squats and squats using a cambered bar. Finally, Gutierrez and Bahamonde (2009) found that peak knee angle was more acute during a free weight back squat compared to a Smith machine squat.

COMPARISON WITH OTHER EXERCISES

Comparing the back squat with other exercises, Hales et al. (2009) compared the peak knee angles in the back squat and deadlift. They reported that the squat displayed a more acute peak knee angle than the deadlift, when performed under powerlifting regulations.

Conclusions

Increasing load and wearing running shoes rather than no footwear appear to lead to more acute peak knee flexion angles. The effect of training status is unclear. Peak knee flexion angles are less acute when using cues to prevent forward knee movement over the toes or as a result of fatigue. Peak knee flexion angle is more acute during the traditional or Olympic weightlifting-style of back squat than during the powerlifting-style of back squat, while the back squat displays a more acute peak knee flexion angle than the Smith machine squat or deadlift.

PEAK ANKLE JOINT ANGLES

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing peak ankle angles in the sagittal plane during the squat exercise

Comparison – between squat variations, between legs, or between lifters of differing expertise

Outcome – peak joint angles (more acute angles are more “closed” while less acute angles are more “open”)

Results 

The following relevant studies were identified that met the inclusion criteria: Zink (2001), Fry (2003), Kellis (2005), Hirata (2007), Braidot (2007), Manabe (2007), Hales (2009), Gutierrez (2009), Lorenzetti (2010), Swinton (2012), List (2013), Sinclair (2014).

Findings

EFFECT OF INTRINSIC FEATURES

Comparing differences between legs during the back squat, Flanagan and Salem (2007) reported that peak ankle angles did not differ between sides.

EFFECT OF TRAINING VARIABLES

Exploring the effects of training variables, Kellis et al. (2005) found that joint angles differed between relative loads but did not identify how the individual hip, knee and ankle joints differed; however, List et al. (2013) found that increasing load caused peak ankle angle to become more acute, from no load to 25% of bodyweight, to 50% of bodyweight. Manabe et al. (2007) found that there was no difference in peak ankle angles between squats performed at slow, moderate or fast speeds.

EFFECT OF EQUIPMENT

Exploring the effects of supportive gear, Zink et al. (2001) found no effect on peak ankle angle of using a weightlifting belt. Sinclair et al. (2014) compared the use of weightlifting shoes, minimalist footwear, running shoes, and no footwear (barefoot) and found that both weightlifting shoes and running shoes displayed more acute peak ankle angles than no footwear but there were no other differences between conditions.

EFFECT OF EXERCISE CUES

Exploring the effects of cues, Hirata and Duarte (2007), Lorenzetti et al. (2010) and List et al. (2013) all found that peak ankle angles were less acute when lifters were visibly cued to prevent the knee from moving forward over the toes, compared to when they were allowed to lift normally.

EFFECT OF HIP JOINT ANGLES

Comparing the effects of squats with different stance widths, Escamilla et al. (2001a) did not report actual peak ankle plantar flexion angles, but they did report more heavily-angled shanks in narrow stance squats compared to wide stance squats.

EFFECT OF SQUAT VARIATION

Comparing squat variations, Braidot et al. (2007) reported that peak ankle angle was similar for the back squat and the front squat. Swinton et al. (2012) found that peak ankle angles were less acute in the order box squat > powerlifting > traditional variations. This appeared to be a function of the near-vertical shank in the box squat and the heavily-angled shank in the traditional squat. Gutierrez and Bahamonde (2009) found that peak ankle angle was more acute during a free weight back squat compared to a Smith machine squat.

COMPARISON WITH OTHER EXERCISES

Comparing exercises, Hales et al. (2009) compared the peak ankle angles in the back squat and deadlift. They reported that the squat displayed a less acute peak ankle angle than the deadlift, when performed under powerlifting regulations.

Conclusions

Using weightlifting shoes and running shoes lead to more acute peak ankle angles than using no footwear, while cues to prevent the knee from moving forward over the toes lead to less acute peak ankle angles. Peak ankle ankles are more acute during traditional back squats than during powerlifting or box squats. They are also more acute during back squats than during Smith machine squats.

SECTION CONCLUSIONS

Greater trunk angles in the back squat are observed in subjects wearing no footwear rather than running shoes and when using cues to restrict the movement of the knees over the toes. The effect of cues to prevent knee movement over the toes on peak hip angle is unclear but cues to look downwards rather than upwards lead to more acute hip angles, while increasing fatigue leads to less acute hip angles.

Increasing load and wearing running shoes rather than no footwear appear to lead to more acute peak knee angles, while using cues to prevent forward knee movement over the toes and fatigue lead to less acute knee angles. Similarly, using weightlifting shoes and running shoes both lead to more acute peak ankle angles than using no footwear, while cues to prevent the knee from moving forward over the toes lead to less acute peak ankle angles.


 

NET JOINT MOMENTS 

PURPOSE

This section sets out a summary of the research that has explored the net joint moments during the squat exercise, using inverse dynamics calculations based on data from motion analysis of joint angle movements and on ground reaction forces measured using a force plate.

LUMBAR JOINT MOMENTS

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing the peak lumbosacral (L5-S1) joint moments in the sagittal plane during the squat exercise

Comparison – between squat variations

Outcome – net joint moment

Results 

The following relevant studies were identified that met the inclusion criteria: Swinton (2012).

Findings

EFFECT OF EXERCISE VARIATION

Comparing different squat variations, Swinton et al. (2012) reported that lumbosacral extensor moments were greater in the traditional squat variation than in either the box or powerlifting squat variations, but there was no difference between box and powerlifting squats.

Conclusions

Lumbosacral extensor moments are greater in traditional back squats than in either box or powerlifting-style squats.

HIP NET JOINT MOMENTS

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing the peak hip net joint moments in the sagittal plane during the squat exercise

Comparison – between squat variations

Outcome – net joint moment

Results 

The following relevant studies were identified that met the inclusion criteria: McLaughlin (1978), Lander (1986), Russell (1989), Wretenberg (1996), Orloff (1997), Escamilla (2001a), Abelbeck (2002), Fry (2003), Hirata (2007), Lorenzetti (2010), Biscarini (2011), Bryanton (2012), Swinton (2012), Biscarini (2013).

Findings

EFFECT OF INTRINSIC FEATURES

Orloff et al. (1997) reported that experienced lifters displayed lower peak hip extensor moments than inexperienced lifters during squats with the same absolute loads. This was associated with the more acute peak trunk angles displayed by the inexperienced lifters, which was taken to imply a greater moment arm length at the hip joint.

EFFECT OF TRAINING VARIABLES

Exploring the effects of training variables, Bryanton et al. (2012) found that peak hip extensor moments increased with increasing relative load (data reported but not analysed directly). Wretenberg et al. (1996) similarly observed that peak hip extensor moment was greater when heavier loads were used, although this was likely also a function of differences between powerlifting and Olympic weightlifting styles of squat. Bryanton et al. (2012) found that peak hip extensor moments increased with increasing depth (albeit with the same absolute loads) but Wretenberg et al. (1996) reported that peak hip extensor moments during both powerlifting squats and during Olympic weightlifting-style squats did not differ substantially between deep and parallel versions (deep = maximal knee flexion vs. parallel = posterior of the hamstrings parallel to the ground).

EFFECT OF EXERCISE CUES

Assessing the effects of cues, Fry et al. (2003) and Lorenzetti et al. (2010) found that peak hip extensor moments were greater when lifters were visibly or forcibly cued to prevent the knee from moving forward over the toes, compared to when they were allowed to lift normally but Hirata and Duarte (2007) found the opposite. McLaughlin et al. (1978) similarly noted that peak hip extensor moments were greater in individuals who displayed greater trunk lean and more acute hip angles, which is associated with this type of exercise cue.

EFFECT OF HIP JOINT ANGLES

Comparing squats with different stance widths, Escamilla et al. (2001a) reported that peak hip extensor moments did not differ between narrow, medium and wide stance squats.

EFFECT OF EXERCISE VARIATION

Comparing squat variations, Russell and Phillips (1989) reported that peak hip extensor moments were greater during the back squat than in the front squat, even when each variation was performed to a standardized depth and with the same relative load. Both Abelbeck (2002) and Biscarini et al. (2011) modeled the effect of changing foot position during Smith machine squats and reported that peak hip extensor moments increased with a foot position that was increasingly further forward of the barbell; similarly, Biscarini et al. (2013) modeled the effect of inclining the Smith machine apparatus backwards or forwards and found that a backward inclination increased hip extensor moments, while a forward inclination decreased them. Wretenberg et al. (1996) found that peak hip extensor moments were greater during powerlifting squats than during Olympic weightlifting-style squats, although this also involved the use of greater absolute loads. Swinton et al. (2012) reported that peak hip extensor moments were greatest in the order powerlifting > traditional > box squat variations. Finally, Lander et al. (1986) compared found no differences in peak hip extensor moments between back squats and squats using a cambered bar.

Conclusions

Hip extensor moments increase with increasing relative load, squat depth, greater trunk lean, and with cues to prevent forward movement of the knees over the toes. They are greater using a powerlifting-style squat than a traditional squat. When using Smith machine squats, hip extensor moments are greater with a foot position that is further forward of the barbell or a backward body inclination.

KNEE NET JOINT MOMENTS

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing the peak knee net joint moments in the sagittal plane during the squat exercise

Comparison – between squat variations

Outcome – net joint moment

Results 

The following relevant studies were identified that met the inclusion criteria: McLaughlin (1978), Lander (1986), Russell (1989), Wretenberg (1996), Stuart (1996), Escamilla (2001a), Wallace (2002), Abelbeck (2002), Fry (2003), Hirata (2007), Gullett (2009), Lorenzetti (2010), Bryanton (2012), Swinton (2012), Biscarini (2013), Cotter (2013).

Findings

EFFECT OF TRAINING VARIABLES

Exploring the effects of training variables, Bryanton et al. (2012) and Cotter et al. (2013) found that peak knee extensor moments increased with increasing depth (albeit with the same absolute loads). Bryanton et al. (2012) reported that peak knee extensor moments did not increase with increasing relative load (data reported but not analysed directly), but Cotter et al. (2013) noted an increase with increasing load. Similarly, Wallace et al. (2002) noted that peak knee extensor moment increased between squats with no load to squats with a barbell load equal to 35% of bodyweight. Wretenberg et al. (1996) found that peak knee extensor moments were greater during both powerlifting squats and during Olympic weightlifting-style squats when performed with greater depth (deep = maximal knee flexion vs. parallel = posterior of the hamstrings parallel to the ground).

EFFECT OF EXERCISE CUES

Exploring the effects of cues, Fry et al. (2003), Hirata and Duarte (2007) and Lorenzetti et al. (2010) all found that peak knee extensor moments were smaller when lifters were visibly or forcibly cued to prevent the knee from moving forward over the toes, compared to when they were allowed to lift normally. McLaughlin et al. (1978) similarly noted that peak knee extensor moments were smaller in individuals who displayed greater trunk lean and more acute hip angles, which is associated with this type of exercise cue.

EFFECT OF HIP JOINT ANGLES

Comparing the effects of squats with different stance widths, Escamilla et al. (2001a) reported that peak knee extensor moments did not differ between narrow, medium and wide stance squats.

EFFECT OF EXERCISE VARIATION

Both Russell and Phillips (1989) and Stuart et al. (1996) reported that peak knee extensor moments were similar during the back squat and front squat, even when each variation was performed to a standardized depth. In contrast, Gullett et al. (2009) reported that peak knee extensor moments were greater during the back squat than the front squat; Both Abelbeck (2002) and Biscarini et al. (2011) modeled the effect of changing foot position during Smith machine squats and reported that peak knee extensor moments decreased with a foot position that was increasingly further forward of the barbell; similarly, Biscarini et al. (2013) modeled the effect of inclining the Smith machine apparatus backwards or forwards and found that a backward inclination decreased knee extensor moments, while a forward inclination increased them. Wretenberg et al. (1996) found that peak knee extensor moments were lower during powerlifting squats than during Olympic weightlifting-style squats, even though the powerlifting squats involved the use of greater absolute loads; Swinton et al. (2012) reported that peak knee extensor moments were greater in the box squat variation than in either the traditional or powerlifting squat variations, but there was no difference between traditional and powerlifting squats. Finally, Lander et al. (1986) found no differences in peak knee extensor moments between back squats and squats using a cambered bar.

Conclusions

Knee extensor moments increase with increasing relative load and squat depth but reduce with cues to prevent forward movement of the knees over the toes or with greater trunk lean. They are greater using a traditional squat than when using a powerlifting-style squat but similar during back and front squats. When using Smith machine squats, knee extensor moments are greater with a foot position that is closer toward the barbell or a forward body inclination.

ANKLE NET JOINT MOMENTS

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing the peak ankle net joint moments in the sagittal plane during the squat exercise

Comparison – between squat variations

Outcome – net joint moment

Results 

The following relevant studies were identified that met the inclusion criteria: Lander (1986), Escamilla (2001a), Hirata (2007), Bryanton (2012), Swinton (2012).

Findings

EFFECT OF TRAINING VARIABLES

Exploring training variables, Bryanton found that peak ankle plantar flexor moments increased with increasing depth (albeit with the same absolute loads) and with increasing relative load (data reported but not analysed directly).

EFFECT OF EXERCISE CUES

Exploring the effects of cues, Hirata and Duarte (2007) found that peak ankle flexor moments were smaller when the knee was cued not to pass forward of the toes compared to a conventional technique.

EFFECT OF HIP JOINT ANGLES

Comparing the effects of squats with different stance widths, Escamilla et al. (2001a) reported that peak ankle plantar flexor moments did not differ between narrow and medium stance squats but were much larger in magnitude during wide stance squats. Additionally, they noted that the net joint moment was an ankle dorsiflexion moment in the medium and wide stance squats but an ankle plantar flexion moment in narrow stance squats.

EFFECT OF EXERCISE VARIATION

Comparing different squat variations, Swinton et al. (2012) reported that peak ankle plantar flexor moments were greater in the traditional squat variation than in either the box or powerlifting squat variations, but there was no difference between box and powerlifting squats. Lander et al. (1986) found no differences in peak ankle plantar flexor moments between back squats and squats using a cambered bar.

Conclusions

Ankle plantar-flexor moments increase with increasing relative load, stance width and squat depth but reduce with cues to prevent forward movement of the knees over the toes.

SECTION CONCLUSIONS

Hip extensor moments increase with increasing relative load, squat depth, trunk lean and with cues to prevent forward movement of the knees over the toes. They are greater using a powerlifting-style squat than a traditional squat. When using Smith machine squats, hip extensor moments are greater with a foot position that is further forward of the barbell or a backward body inclination.

In contrast, knee extensor moments increase with increasing relative load and squat depth but reduce with cues to prevent forward movement of the knees over the toes or with greater trunk lean. They are greater using a traditional squat than when using a powerlifting-style squat but similar during back and front squats. When using Smith machine squats, knee extensor moments are greater with a foot position that is closer toward the barbell or a forward body inclination.

Ankle plantar-flexor moments increase with increasing relative load, stance width and squat depth but reduce with cues to prevent forward movement of the knees over the toes.


EXTERNAL MOMENT ARM LENGTHS

PURPOSE

This section sets out a summary of the research that has explored the external moment arm lengths at the hip, knee and ankle during the squat exercise.

EXTERNAL MOMENT ARM LENGTHS: SPINE

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing the external moment arm lengths at the lumbar spine in the sagittal plane during the squat exercise

Comparison – the anatomical position or between squat variations

Outcome – external moment arm length

Results 

The following relevant studies were identified that met the inclusion criteria: Swinton (2012).

Findings

EFFECT OF EXERCISE VARIATION

Comparing different squat variations, Swinton et al. (2012) reported that peak lumbosacral moment arm lengths were greater in the traditional and powerlifting squat variations than in the box squat variations. However, there was no difference between the traditional and powerlifting squat variations.

Conclusions

Lumbosacral moment arm lengths are greater in the traditional and powerlifting squat styles than in the box squat style.

EXTERNAL MOMENT ARM LENGTHS: HIP

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing the external moment arm lengths at the hip in the sagittal plane during the squat exercise

Comparison – the anatomical position or between squat variations

Outcome – external moment arm length

Results 

The following relevant studies were identified that met the inclusion criteria: Escamilla (2001a), Swinton (2012).

Findings

EFFECT OF HIP JOINT ANGLE

Comparing the effect of squats with different stance widths, Escamilla et al. (2001a) reported no differences in hip moment arm lengths between the narrow, medium, and wide stance width squats at any point in the lowering and lifting phases, except at 45 degrees of knee flexion in the lifting phase, when the medium and wide stance width squats displayed greater hip moment arm lengths than narrow stance width squats.

EFFECT OF EXERCISE VARIATION

Comparing different squat variations, Swinton et al. (2012) reported that peak hip extension moment arm lengths were greater in the traditional and powerlifting squat variations than in the box squat variations. However, there was no difference between the traditional and powerlifting squat variations.

Conclusions

Hip extensor moment arm lengths are greater in the traditional and powerlifting squat styles than in the box squat style.

EXTERNAL MOMENT ARM LENGTHS: KNEE

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing the external moment arm lengths at the knee in the sagittal plane during the squat exercise

Comparison – the anatomical position or between squat variations

Outcome – external moment arm length

Results 

The following relevant studies were identified that met the inclusion criteria: Escamilla (2001a), Swinton (2012).

Findings

EFFECT OF HIP JOINT ANGLE

Comparing the effect of squats with different stance widths, Escamilla et al. (2001a) reported no differences in knee moment arm lengths between the narrow, medium, and wide stance width squats at any point in the lowering and lifting phases, except at 45 degrees of knee flexion in both lowering and lifting phases, when the wide stance width squats displayed greater knee moment arm lengths than either medium or narrow stance width squats.

EFFECT OF EXERCISE VARIATION

Comparing different squat variations, Swinton et al. (2012) reported that peak knee extension moment arm lengths were greatest in the order box > traditional > powerlifting squat variations.

Conclusions

Knee extensor moment arm lengths are greatest in the order box > traditional > powerlifting squat styles.

EXTERNAL MOMENT ARM LENGTHS: ANKLE

Selection criteria

Population – any healthy, adult population

Intervention – any acute study assessing the external moment arm lengths at the ankle in the sagittal plane during the squat exercise

Comparison – the anatomical position or between squat variations

Outcome – external moment arm length

Results 

The following relevant studies were identified that met the inclusion criteria: Escamilla (2001a), Swinton (2012).

Findings

EFFECT OF HIP JOINT ANGLE

Comparing the effect of squats with different stance widths, Escamilla et al. (2001a) reported differences in ankle moment arm lengths between narrow, medium, and wide stance width squats at most points in the lowering and lifting phases. In general, wide stance width squats displayed large, negative ankle moment arm lengths, medium stance width squats displayed small, negative ankle moment arm lengths, and narrow stance width squats displayed small, positive ankle moment arm lengths.

EFFECT OF EXERCISE VARIATION

Comparing different squat variations, Swinton et al. (2012) reported that peak ankle moment arm lengths were greater in the traditional squat variation than in either the powerlifting or box squat variations. However, there was no difference between the powerlifting and box squat variations, and only positive ankle moment arm lengths were observed for all types of squat.

Conclusions

Ankle moment arm lengths are greater in the traditional squat style than in either the powerlifting or box squat styles.

SECTION CONCLUSIONS

Lumbosacral, hip extensor moment and ankle arm lengths are greater in the traditional and powerlifting squat styles than in the box squat style. In contrast, knee extensor moment arm lengths are greatest in the order box > traditional > powerlifting squat styles. 

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