How can ballistic training programs best improve power?

Developing strength and muscle mass are key for athletic development but muscular power is thought to be even more important. Ballistic resistance-training is commonly used for increasing muscular power. However, there is no strong consensus regarding how to set-up training variables during this type of training. Here is a review of the long-term training studies to help clarify things a little.

What is the background?

For an in-depth discussion of muscular power, see my previous article on how to maximize power gains in resistance-training. Exactly how the different training modalities stack up against one another will be covered in a future blog post.

What is ballistic resistance-training?

Ballistic resistance-training differs from heavy resistance-training insofar as there is no deceleration part to the concentric phase. This means that trainees can accelerate throughout the whole concentric range of motion (ROM). It has been proposed that this greater length of time spent accelerating may be advantageous for causing muscular adaptations. Additionally, ballistic resistance-training tends to differ from heavy resistance-training in that lighter loads tend to be used. This means that the loads used are closer to the load at which maximum power output is generated. Given that load-specificity is frequently observed in adaptations to training, this may be part of the reason why ballistic resistance-training is thought to be so important: the measurements involve recording power outputs at values that are close to the loads that are actually used during ballistic resistance-training.

What problems do we have with definitions?

There are some tricky issues with regard to definitions when it comes to differentiating between heavy-load resistance-training using different loads, ballistic resistance-training, and plyometrics. The primary issue here is that whether lifts are ballistic or non-ballistic should strictly be determined by biomechanics and not load but in practice there tends to be a bit of wiggle-room here. A secondary issue is the fact that “no-load” is often used as a loading parameter because it has been found in acute trials to lead to maximal power outputs during vertical jumps (power output during vertical jumping is the most commonly-used test in the literature).

Researchers often refer to “power-based” resistance-training with lighter loads but are then vague about whether or not the exercise was ballistic. Technically, for a movement to be properly categorized as “ballistic”, there must be no deceleration section to the concentric phase. As noted above, this is more than just a technicality, as the benefit of performing ballistic lifts may arise because it is possible to accelerate for a longer period of time and achieve superior adaptations over the long-term. Therefore, for the purposes of this review, if a training exercise was classified as “power-based” but it was not explicitly specified that the athlete performed a ballistic movement, this was classified as a fast, heavy-load resistance exercise and not included. Conversely, if it was explicitly specified that the athlete performed a ballistic movement, irrespective of the load used, this was classified as a ballistic exercise and included.

Additionally, since no-load is often the load that maximizes power output during vertical jumps, there is a tendency in the literature to compare squat jumps with different loads and to include no-load as a loading parameter. In this case, we are technically comparing a plyometric exercise (i.e. using bodyweight only) with a ballistic resistance-training exercise (i.e. using an added external load during a ballistic resistance-training exercise). Similarly, there is also a tendency to compare weighted countermovement jumps (which are ballistic resistance-training exercises using the above definition) with un-weighted countermovement jumps, since again no-load is treated as a load. Once again, here we are technically comparing plyometrics with a ballistic resistance-training exercise. However, since no-load is such a popular “load” to use, for completeness, where studies have compared similar movements with and without load, the no-load condition has been classified into this review as a ballistic resistance-training exercise.

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Which ballistic training variables improve power outputs most?

What are the underlying biological mechanisms?

It is unclear exactly how ballistic resistance-training leads to improvements in power output. Some researchers (Cormie, 2011) have suggested that there are increases in neural drive, rate of neural activation, and inter-muscular co-ordination, which together cause an improvement in rate of force development (RFD). Indeed, Winchester (2008) found that an 8-week period of ballistic resistance-training using jump squats caused an improvement in both RFD and power outputs. However, the precise nature of the underlying adaptations causing these improvements is unclear and it seems likely that some local muscular changes also occur.

What are the selection criteria?

The following studies assessed the effects of altering selected training variables on improvements in muscular power during ballistic resistance-training long-term experimental trials (excluding Olympic weightlifting, which will be addressed separately). The main three criteria used to select the studies were strictly enforced, as follows:

The outcome measure of the study had to be a measured or muscular power that was expressed in Watts and was not a proxy (e.g. vertical jump height).

The study had to explore the effects of a specific resistance-training variable by using at least two different interventions in which only a single variable was altered (e.g. rest periods, or relative load) within the boundaries of what is possible.

The study had to only involve ballistic resistance-training and not carry out ballistic resistance-training in combination with other training modalities, such as heavy resistance-training, Olympic weightlifting or its variations, or plyometrics in combined interventions.

As you will see from the review, this set of rather straightforward criteria has a quite radical effect on the number of qualifying studies. This is partly because many early studies used vertical jump height as a proxy for power output and partly because many later studies have assessed combined methods.

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Effect of relative load

The following table summarizes the results of the long-term trials investigating the effect of relative load during ballistic resistance-training on gains in muscular power. The details of the studies are provided afterwards.

Relative load ballistic

McBride (2002) compared the effects of heavy and light jump squats on peak power output in 26 athletic males with some resistance-training experience, training twice per week over an 8-week period. The subjects were randomly allocated into a light-load, a heavy-load, or a control group. The training groups performed sessions of jump squats with either 30% or 80% of back squat 1RM. The researchers reported that the light group significantly increased peak power output during a jump squat test with 30% of 1RM but the heavy group did not (~10% vs. ~4%). There were no significant differences between the two groups. The researchers found that both light and heavy groups significantly increased peak power output during a jump squat test with 80% of 1RM and there was a non-significant trend for the light group to increase power output to a greater extent (~18% vs. ~14%). Finally, in a jump squat test with 55% of 1RM (mid-way between the two training loads), the researchers also found that both light and heavy groups significantly increased peak power output and there was a non-significant trend for the light group to increase power output to a greater extent (~14% vs. ~10%).

Smilios (2013) compared ballistic resistance-training with heavy loads and with loads that maximized power output in 43 moderately trained male subjects. The subjects were randomly allocated into 4 groups, including 1 heavy-load group (90% of 1RM), 2 ballistic groups at loads where power output was maximized (1 with body mass in the calculations [PW+] and 1 without body mass in the calculations [PW-]), and 1 control group. The subjects performed 4 – 6 sets of jump squats for 6 weeks. The heavy load group performed 3 repetitions at 90% of 1RM. The maximal power output groups used loads of 48 – 58% of 1RM (PW-) and 20 – 37% of 1RM (PW+). All groups also performed 6 repetitions of jump squats with no load. The researchers found that heavy load group and the PW- group both significantly increased power output at loads of 20, 35, 50, 65, and 80% of 1RM while the PW+ group only significantly increased power output at loads of 20 and 35% of 1RM.

Marcovic (2013) compared the effects of different external loads during vertical jump training on muscular power output during the squat and countermovement jumps in physically active but untrained males over an 8-week period. The loading conditions were: no-load and a weighted vest equal to 30% of body weight. The researchers found that the training period led to similar increases in power in the squat jump (7.4 – 11.5 %) but there were differences between groups in respect of the countermovement jump (0.5 vs. 9.5%), whereby the weighted vest group displayed superior results in power output than the no-load group.

Harris (2008) compared the effects of heavy and light jump squats on peak power output in 18 well-trained rugby league players training over a 7-week period. The subjects were randomly allocated into volume-matched heavy load (80% of 1RM) or a light load (20 – 44% of 1RM) groups. The heavy load groupperformed 5 sets of 5 repetitions with a 2-minute rest between sets and the light-load group performed 6 sets of 10 – 12 repetitions with a 2-minute rest between sets. Before and after the intervention, the researchers measured maximal power output at 55% of pre-training 1RM. They found that peak power output actually decreased in both groups but the reduction was significantly smaller in the light-load group compared to the heavy-load group.

In summary, the evidence is conflicting regarding the best load to use during ballistic resistance-training exercise for maximizing gains in muscular power, as two studies found a significant effect in favor of heavy loads and two studies found significant effects in favor of light loads.

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Effect of muscle action

The following table summarizes the results of the long-term trials investigating the effect of muscle action during ballistic resistance-training on gains in muscular power. The details of the studies are provided afterwards.

Muscle action ballistic

Hori (2008) compared the effects of weighted jump squat training with and without eccentric braking in 20 male subjects. The researchers randomly allocated the subjects into 2 groups who trained for an 8-week period. The non-braking group performed of 6 sets of 6 repetitions of weighted jump squats while the braking group performed the same training but the eccentric loading was reduced by using an electromagnetic braking mechanism. The braking group displayed superior adaptations in peak power relative to body mass in the weighted jump squat.

Vanderka and Novosád (2012) compared the effects of explosive squat jump training with and without counter movement in 30 physically active, male subjects. The subjects all trained 2 times per week for 11 weeks, twice a week. One group trained always using a countermovement and the other group always trained using no countermovement. Both groups progressed from 3 to 6 sets of 6 repetitions of weighted explosive squats using relative loads of 50 – 70% of 6RM. The researchers found that the increase in power output was significant and similar in both groups.

Hoffman (2005) compared two protocols of jump squat training in 47 college football players with resistance-training experience over a 5-week period. The subjects were randomly assigned to 1 of 3 groups: a stretch-shortening cycle group, a concentric-only group, and a control group. The stretch-shortening cycle group performed jump squats in addition to their standard training with 70% of 1RM back squat using a jump squat machine apparatus. The load was applied in both concentric and eccentric phases of the exercise. The concentric-only group performed the same jump squat protocol but with the load applied only in the concentric phase. This was possible because the apparatus allows each phase to be loaded individually. The researchers did not identify any significant changes in respect of power output nor any differences between the groups in respect of the changes in power output.

In summary, there is conflicting evidence regarding whether avoiding the use of eccentric muscle actions during ballistic resistance-training exercise can improve gains in muscular power, as two of three studies found that there was no difference between concentric-only and stretch-shortening cycle jumps on increases in power output, while a third found that concentric-only muscle actions led to superior results.

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How can we summarize these findings?

For maximizing muscular power using ballistic resistance-training, there is little or no evidence from long-term trials to help us decide which volumes, frequencies, and ranges-of-motion to use. In respect of relative load, it seems that the literature is conflicting and both heavy and light relative loads can be used successfully for increasing muscular power. In respect of muscle action, there is limited evidence to support the use of concentric-only muscle actions for increasing muscular power.

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What are the practical implications?

There is little evidence to preferentially use heavy-load or light-load ballistic resistance-training for increasing muscular power. Variety in loading protocols can therefore be used as required.

There is little evidence to preferentially use stretch-shortening cycle or concentric-only ballistic resistance-training for increasing muscular power. Variety in these two different types of exercise protocol can therefore be used as required.

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How can resistance-training programs best improve power?

Developing strength and muscle mass are key for athletic development but muscular power is thought to be even more important. Conventional (non-ballistic) resistance-training has been found to improve power but exactly how to program it is unclear. How should we alter individual training variables such as volume, relative load (percentage of 1RM), training frequency, range-of-motion (ROM), and rest period duration to optimize gains in muscular power? In this article, Chris reviews the literature…

What is the background?

Cautionary note: This background section is very long and while it starts off by looking at very basic issues, it gets quite technical extremely quickly. If you’d prefer just to look at how to program conventional (heavy-load) resistance-training for maximal gains in power output, please skip down to the review by clicking HERE.

What is power?

In strict Newtonian mechanical terms, power is defined as the product of force (in Newtons) and velocity (in meters per second). So power can be expressed as a value in Newton meters per second but it is more commonly reported as Watts (i.e. a Watt is synonymous with a Newton meter per second). Power can also be calculated as the rate at which work is done, where work done is the product of force (in Newtons) and distance (in meters). Despite the availability of such a precise definition, Cronin and Sleivert (2005) have noted that power is frequently confused with other measures in many places in the sports science literature, such as rate of force development (RFD), explosive strength, and impulse. We are not going to fall into that trap here, so everything in this review will be related to a power output measure in either Watts or Newton meters per second.

What is muscular power?

In biomechanics literature, muscular power is often discussed without clearly defining the exact terms, particularly where compound movements are being investigated. Strictly speaking, if we want to explore the ability of a given muscle to produce power, then short of doing some musculoskeletal modelling, we will need to calculate power as the product of joint moment and angular velocity. This can very easily be done in single-joint, or isolation movements such as knee extensions or biceps curls and the output is a measure of joint power, which involves all of the muscles acting on the joint. However, when exploring compound movements, things become more complicated, as we will see later on. Nevertheless, irrespective of whether we are investigating isolation or compound movements, if we are going to understand power, then we need to understand how changing either force (or joint moment) or velocity (or angular velocity) affects the other. We can do this most easily by looking at the force-velocity relationship.

What is the force-velocity relationship?

Individual muscles are thought to follow a fairly predictable force-velocity relationship, which is negative and hyperbolic. Being negative means that the greater the external load, the lower the contraction velocity. Similarly, the higher the contraction velocity, the lower the internal muscle tension. Being hyperbolic means that the rate of change of force alters with changing velocity. At low velocities, the rate of change of force is very high and it drops off quickly with small increments in speed. At higher velocities, the rate of change of force is quite low and alters little with each incremental change in speed. The force-velocity relationship was originally described by Hill (1938) and his formula includes two constants as well as maximum isometric force. The following diagram (see original here) presents this force-velocity relationship and its consequences for muscular power.

Force-velocity

The diagram shows that while force decreases rapidly as velocity increases, the product of force and velocity (i.e. power) is greatest when both force and velocity are moderate values rather than when either force or velocity is very high. Thus, we can deduce that power outputs are most likely to be greatest when moderate loads and moderate velocities are used.

What factors determine muscular power?

Power is determined by the ability to produce force and the speed of the muscular contraction. Therefore, the ability of a muscle to produce power is thought to be affected by the underlying qualities of a muscle that affect force production and contraction velocity. Factors that affect joint moment production during simple concentric-only muscle actions include moment arm length, fiber type, cross-sectional area, fascicle length, pennation angle, motor unit recruitment, and motor unit firing frequency. Factors that affect force production during stretch-shortening cycle muscle actions also include tendon compliance. Factors that affect contraction velocity during simple concentric-only muscle actions include fiber type, fascicle length, pennation angle, and motor unit firing frequency. Factors that affect contraction velocity during stretch-shortening cycle muscle actions also include tendon compliance. That means there are a lot of potential factors that could influence changes in power output during a program of resistance-training!

Are compound movements different from isolation movements?

Most studies exploring muscular power are primarily interested in its development for athletic movement. Thus, power outputs during compound exercises involving lower-body movements (e.g. jumping) are most frequently investigated. However, there is a crucial difference between compound and isolation movements when it comes to measuring power outputs. When we measure power outputs during compound exercises, we are not measuring the individual muscular power outputs but rather the ability of a combination of a group of muscles acting together in a system to produce power. Thus, in addition to the factors affecting individual muscle power noted above, there will be factors associated with the system that will also affect the system power outputs measured during compound exercises. Such factors include synergist activation, antagonist co-contraction, and the extent to which proximal-to-distal kinematic sequencing occurs in the motor pattern. So compound movements are quite different from isolation movements when it comes to measuring power output and they may also have their own specific adaptations as well.

How do compound movements differ from isolation movements?

One really important way in which compound and isolation movements differ is the way in which system power outputs change with the imposed external load. Obviously, in the case of isolation movements, the system power output at any given loading is the same as the individual muscle group power output. However, the same is not the case in compound movements. Bobbert (2012) devised a musculoskeletal model to explore why the force-velocity relationship observed in a lower body compound movement (leg pressing) is not hyperbolic but is almost linear. The model showed that even though there was a hyperbolicforce-velocity relationship between leg extension velocity and muscle force, segmental dynamics canceled increasingly more muscular force as movement velocity increased and external force reduced. Thus, while maximum possible muscular force and maximal possible muscle contraction velocity are the only two key variables relevant to single-joint movements, segmental dynamics must also be considered as a key variable in compound movements. Moreover, this phenomenon may have training implications. Bobbert reported that while external power output peaked when external force was ~50% of maximum, muscle power output peaked when external force was ~15% of maximum. Thus, training at moderate loads would lead to maximum system power outputs, while training with lower loads would maximize individual muscle power outputs. If maximizing power output of individual muscles is central to developing the ability of a muscle to produce power over a long-term training intervention, then this would imply that optimizing power outputs by reference to the system is not the best way to achieve this aim.

What is the load that maximizes power output?

Some researchers have suggested that training with a load that optimizes power output will lead to the greatest long-term adaptations. For a detailed review of this topic, see Cronin and Sleivert(2005). As a consequence, many studies have investigated the load that maximizes power output in various exercises. This load seems to depend upon the exercise. For example, Baker (2001) reported that the load that maximizes power output during explosive bench press-type throws in a smith machine was 55 ± 5.3% of 1RM bench press. However, many tests of lower body power output during jumping have found that the load that maximizes power output is no-load (e.g. Cormie, 2007).

These observations have led to the maximum dynamic output (MDO) hypothesis, which is the proposal that the arrangement of the lower body segments is such that it can produce maximum dynamic power output in rapid movements when loaded only by the weight and the inertia of its own body (Jaric and Markovic, 2009). Thus, when performing jump squats, maximum power output is expected to occur with no load. The exact type of jump may have a bearing on the validity of the MDO hypothesis. For example, Swinton (2012) found that while conventional jump squats displayed maximum power output with no external load, hex-bar deadlift jumps displayed peak power output with 20% of 1RM additional load. It was once proposed that training status may also affect the point at which peak power is produced, as Baker (2001) reported that a load of 55% of 1RM maximized power output during jump squats in well-trained athletes. More recently, however, both Nuzzo (2010) and Pazin (2013) have found that bodyweight leads to maximal power output during jump squats in a range of individuals with differing training statuses.

Why is the optimum load for power during jump squats so low?

When we are exploring the power output during a lower-body compound exercise, we are almost always moving the body through space. It is easy to forget that this means there is a substantial load being moved, particularly where strength and power athletes are concerned. For example, “no-load” during a jumping movement is actually a fairly large relative load for the muscles while “no-load” during a throwing action really does mean almost no load. This can be confusing when reviewing the literature, as many studies have reported that the load that leads to optimum power output during the countermovement jump is no-load. If we are not careful, we might fall into the trap of assuming that this does not abide by the force-velocity relationship noted above. However, Pazin (2013) noted that while maximal power output occurred at bodyweight, when including bodyweight in the calculations of overall weight lifted, the average load that maximized peak and mean power output during different types of jump was 30 – 46% of maximal dynamic strength. So power is still being maximized at moderate loads, it’s just that we don’t tend to incorporate the load of the body when we measure 1RM squat load.

Is muscular power a key predictor of athletic performance?

It is often assumed without question that the ability to generate a large power output during compound movements is a key differentiator of athletic performance. However, as Cronin and Sleivert(2005) have noted, much of the evidence for this is based on studies that have used inaccurate outcome measures for measuring power. It may be the case that other strength qualities such as impulse, rate of force development, or explosive strength may be better predictors of athletic performance. Nevertheless, it is not the purpose of this review to explore such issues but rather to explore the optimal ways in which power can be developed, where it is considered to be a valuable quality.

What might we expect to see in long-term training studies?

Based on this short review, in long-term training studies we might expect to see the following:

Gains in muscular power output as a result of interventions that enhance muscular strength, such as heavy resistance-training, ballistic resistance-training, plyometrics, and Olympic weightlifting.

Gains in muscular power output as a result of interventions that enhance contraction velocity, which include the same interventions.

Since muscular strength is a lot easier to improve than muscle contraction velocity, we might expect training methods that enhance strength to have a greater effect than methods directed solely towards increasing contraction velocity, particularly in populations for whom it is easy to enhance strength, such as untrained subjects.

Maximum power outputs recorded when moderate loads and moderate velocities are used. Thus, if the outcome measure is solely maximum power output and is not assessed at different relative loads, training specificity might be expected to lead to the apparent greater success of those methods that enhance the force-velocity relationship at these moderate loads.

Training status not being a major factor affecting the force-velocity relationship. Although training specificity may have some affect on performance at different loads, maximum power output is still anticipated to remain at similar percentages of maximum strength in power athletes.

Differences in results between isolation exercises and compound movements, as there are more variables in play and an added degree of complexity, which makes exact training responses difficult to predict.

The complexity and lack of certainty provide a very good reason not to place too much faith in acute trials and to review how training variables affect gains in muscular power during long-term training studies.

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THE REVIEW

Which resistance-training variables improve power outputs most?

What are the underlying biological mechanisms?

Resistance-training can increase muscular cross-sectional area (and therefore also moment arm lengths), fascicle lengths, pennation angle, motor unit recruitment, motor unit firing frequency, co-ordination, and synergist activation. Thus, there is a sound underlying set of biological mechanisms through which resistance-training might alter and likely improve muscular power output.

What are the general effects of resistance-training?

Resistance-training has been found to improve absolute force and peak power at the individual fiber level (Widrick, 2002; Shoepe, 2003) and may also improve contractile velocity (Trappe, 2000). Many studies have confirmed increases in power output at the muscular level when tested during isolation movements such as biceps curls (Moss, 1997; Toji and Kaneko, 2004). Trials investigating muscular power outputs following interventions using compound exercises have also generally observed improvements (Jozsi, 1999; Häkkinen, 2001; Izquierdo, 2001; Ferri, 2003) in both young and old individuals.

What are the selection criteria for this review?

The following studies assessed the effects of altering selected training variables on improvements in muscular power during heavy resistance-training long-term experimental trials. The main three criteria used to select the studies were strictly enforced, as follows:

The outcome measure of the study had to be a measured on muscular power that was expressed in Watts and was not a proxy (e.g. vertical jump height).

The study had to explore the effects of a specific resistance-training variable by using at least two different interventions in which only a single variable was altered (e.g. rest periods, or relative load) within the boundaries of what is possible.

The study ideally had to only involve dynamic heavy resistance-training and not carry out heavy resistance-training in combination with other training modalities, such as ballistic resistance-training or plyometrics in combined interventions. However, since athletes perform other training and engage in explosive movements during sports anyway, this criterion was relaxed where trained populations were involved.

N.B. This review does NOT cover ballistic resistance-training and this will be covered in the next article.

As you will see from the review, this set of rather straightforward criteria has a quite radical effect on the number of qualifying studies. This is partly because many early studies used vertical jump height as a proxy for power output and partly because many later studies have assessed combined methods. While some may consider this overly strict, it is worth noting that the use of jump height to measure power was challenged as long ago as 2005 by Cronin and Sleivert (2005). Exactly why this is the case is probably a step too far for this article but I shall cover it in a future instalment. Suffice it to say that there is more involved in a big vertical jump than just power output, so trying to draw conclusions about power output from vertical jump height isn’t really valid.

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What is the effect of relative load?

The following studies have assessed how relative load affects gains in muscular power. For a refresher, read more about how relative load affects gains in muscular size and about how relative load affects gains in muscular strength in previous reviews. Here’s a table to summarize the results of relative load on power improvements:

Load for power

Moss (1997) explored the effects of strength training with different loads on muscular power output of the elbow flexors in 30 physical education students divided into 3 groups. One group trained using 2 repetitions and a load of 90% of 1RM, another with 7 repetitions and a load of 35% of 1RM, and one with 10 repetitions and a load of 15% of IRM. All groups trained using 3 – 5 sets, 3 times a week for 9 weeks. Maximal power increased for all tested loads in all 3 groups and there were no significant differences in this increase in power among the 3 groups at loads <50%. However, for loads >70% of 1RM, the increase in muscular power output was significantly larger for the heavier two groups (90% of 1RM and 35% of 1RM) than for the lightest group (15% of 1RM). The researchers also observed a trend towards load-specificity, in that the load at which each group trained was the load at which the greatest power outputs were observed.

Harris (2000) explored the effects of 3 different resistance-training methods on power output during the vertical jump in 42 resistance-trained males. The researchers randomly assigned the subjects into a high force (80 – 85% of 1RM), a high power (30% of 1RM), and a combination group for a 9-week intervention. However, neither the high force group nor the high power group significantly improved vertical jump peak or average power outputs. The improvements in the high force and high power groups were similar for both average (3.1% and 2.1%) and peak power (2.6% and 2.4%) in that there was a small trend for an improvement in both cases but there was no real difference between groups.

Cronin (2001) investigated the effect of isoinertial training velocity on netball chest pass throwing power and velocity in 21 female netball players during a 10-week intervention. The researchers randomly assigned the subjects either to a strength group (80% of 1RM), a power group (60% 1RM), or a control group. The researchers found that the strength group produced significantly greater improvement in mean power output compared to the power and control groups.

De Vos (2005) compared the effects of three different loads (20%, 50% and 80% of 1RM) during resistance-training for improving muscle power in 112 healthy older adults (69 ± 6 years). The subjects trained 2 times per week with 5 exercises for 3 sets of 8 repetitions using resistance machines. The researchers found that average peak power increased significantly and similarly in 80% (14 ± 8%), 50% (15 ± 9%), and 20% (14 ± 6%) groups compared to a control group (3 ± 6%). The researchers concluded that peak muscular power may be improved similarly using light, moderate, or heavy relative loads in elderly people.

Rana (2008) compared the effects of relative load on muscular power increases in 34 healthy adult females who performed a 6-week resistance-training program comprising the leg press, back squat and knee extension. The researchers allocated the subjects into different groups. One group performed traditional heavy strength-training group at 6 – 10 RM with 1 – 2 second concentric and eccentric phases. Another group performed traditional endurance-training at 20 – 30RM with 1 – 2 second concentric and eccentric phases. The researchers found that there were no significant changes in muscular power in any group as a result of the intervention. However, there was a non-significant trend for the traditional heavy strength-training to display a greater increase in muscular power during the vertical jump test (c. 8.3%) than the traditional endurance-training group (c. -1.2%).

Jones (2001) compared power output following a 10-week period of heavy resistance-training with two different loading protocols in 30 moderately resistance-trained NCAA Division I baseball players. The subjects were randomly assigned to either low-load (40 – 60% of 1RM) or high-load (70 – 90% of 1RM) groups, who trained using the parallel squat, Romanian deadlift, lunge, and partial squat exercises. Before and after the intervention, the researchers tested power outputs during squat jumps, depth jumps, and weighted jumps with 30 and 50% of 1RM. There was no significant improvement in power outputs measured during the squat jump and depth jump for either group, nor was there any significant difference between groups. Both high- and low-load groups similarly improved power output during both types of jump squat but the low-load group improved power output to a significantly greater extent.

De Villarreal (2012) compared the effects of heavy-load resistance training and light-load resistance-training in 65 physical education students (47 males and 18 females). The heavy-load resistance training group trained using the full-squat exercise with 56 – 85% of 1RM for 3 – 6 repetitions and the light-load strength training trained using the parallel-squat exercise with 100 – 130% of the load that maximizes power output for 2 – 6 repetitions. The researchers reported no significant differences in power output during loaded jumps between the two training programs.

In summary, this limited group of studies shows that muscular power can be enhanced similarly by a wide range of loads during resistance-training. There is certainly no strong trend in favour of either heavy or light loads. Thus, as Cronin and Sleivert (2005) suggest, it may be that load is not as important as is generally assumed for developing power. Rather, other factors may be more important.

Additionally, the results from several studies indicate that muscular power is developed in a way such that power output is maximized at the load used during training. This may indicate that the load selected for developing power for sports-specific purposes should be the load closest to that which is required during play. However, it is also possible that a variety of loads may be optimal and further research is needed in this area.

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What is the effect of repetition speed?

The following studies have assessed how repetition speed affects gains in muscular power. For a refresher, read more about how repetition speed affects gains in muscular size and about how repetition speed affects gains in muscular strength in previous reviews. Here is a table to summarize the results:

Speed for power

Morrissey (1998) explored the effect of repetition speed in a 7-week trial in which two groups of untrained female subjects performed squats in one of two conditions, being either slow (2 seconds up and 2 seconds) or fast (1 second up and 1 second down) for 3 sets of 8 repetitions to muscular failure, 3 times per week. The researchers found that increases in system peak power during the vertical jump were very similar in both groups (slow = 10% ± 10% vs. fast 9% ± 5%), as were the increases in system average power (slow = 35% ± 15% vs. fast 30% ± 9%).

Rana (2008) compared the effects of relative load on muscular power increases in 34 healthy adult females who performed a 6-week resistance-training program comprising the leg press, back squat and knee extension. The researchers allocated the subjects into different groups. One group performed traditional training at 6 – 10 RM with 1 – 2 second concentric and eccentric phases. Another group performed slow training at 6 – 10RM but with a 10-second concentric and a 4-second eccentric phase. The researchers found that there were no significant changes in muscular power in any group as a result of the intervention. However, there was a non-significant trend for the traditional group to display a greater increase in muscular power during the vertical jump test (c. 8.3%) than the slow group (c. 0.0%).

Neils (2005) assessed the adaptations following traditional (80% of 1RM) and SuperSlow resistance-training (50% of 1RM) using the squat exercise in 16 healthy, untrained subjects. The subjects trained 3 days per week for 8 weeks. The researchers reported that the traditional group improved peak power during the countermovement jump significantly from 23.0 ± 5.5 to 25.0 ± 6.3 W/kg but there was no significant increase in the SuperSlow group.

Kraemer (2001) compared the effects of two periodized resistance training programs in which a power-training group emphasized explosive exercise movements using 3 – 8RM training loads and a strength-hypertrophy group emphasized slower exercise movements with 8 – 12RM loads. Only the power-training group displayed increased in squat jump and bench throw power outputs compared to a control.

Fielding (2002) compared the effects of high-velocity and low-velocity resistance-training programs in 30 elderly women (aged 73 + 1 years). The subjects trained 3 times per week for 16 weeks with 3 sets of 8 – 10 repetitions of the leg press and knee extension exercises at 70% of 1RM. The researchers found that leg press peak power increased significantly more in the high-velocity group than in the low-velocity group.

In summary, while the literature is not completely consistent, there are some indications that a faster repetition speed is superior to a slow repetition speed for increasing muscular power, where repetition speed is deliberately slowed rather than being a function of relative load.

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What is the effect of volume?

The following studies have assessed how training volume affects gains in muscular power. For a refresher, read more about how training volume affects gains in muscular size and about how training volume affects gains in muscular strength in previous reviews.

Ostrowski (1997) investigated the effects of 3 different volumes (low, moderate and high) of resistance training on muscle size over a 10-week period in 27 males with 1 – 4 years weight-training experience, training 4 days a week. Pre- and post-intervention, the researchers measured vertical jump power output and bench throw power output. The researchers reported that the vertical jump power output did not increase in any group but the bench throw power output increased in all three groups. There was no significant difference between any of the groups and the increases in bench throw power outputs were all very similar, ranging between 2.3 – 3.1%.

Naclerio (2013) compared the effects of 3 different resistance-training volumes (1 set, 2 sets, and 3 sets per exercise) on maximum strength in 32 college team sport athletes (20 males and 12 females) with no previous resistance-training experience over a 6-week intervention. The researchers found that only the 2-set and 3-set groups increased average power output for the bench press but only the 1-set group increased average power output for the squat.

Stone (A short term comparison of two different methods of resistance training on leg strength and power) compared the effects of different training modalities (machines and free-weights), different training volumes (1 set vs. 3 – 7 sets), and different numbers of repetitions. They reported that there was no significant difference in vertical jump power output in either group.

In summary, there is no clear picture regarding the effects of training volume on increases in muscular power following resistance-training interventions.

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What is the effect of proximity to failure?

The following studies have assessed how proximity to failure affects gains in muscular power. For a refresher, read more about how proximity to failure affects gains in muscular size and about how proximity to failure affects gains in muscular strength in previous reviews.

Izquierdo (2006) assessed the effects of training to failure or not-to-failure during 11 weeks of resistance-training in 42 physically-active males. The researchers reported that both groups significantly improved upper and lower body power but there were no significant differences between groups. Upper body power increased in the failure and not-to-failure groups by 20% and 23% and lower body power increased by 26% and 29%. Thus, there was a slight non-significant trend for the failure group to improve upper and lower body power to a greater extent.

Drinkwater (2006) assessed the effect of training to repetition failure on 40kg bench throw power in elite junior athletes. The subjects performed bench press training for 3 workouts per week for 6 weeks, using equal volume in one of two groups. One group trained to repetition failure by using 4 sets of 6 repetitions every 260 seconds while the other group trained using the same number of total repetitions but not to failure, using 8 sets of 3 repetitions every 113 seconds. The researchers found that the failure group displayed greater increases in bench throw power.

Lawton (2004) compared the effects of two training protocols in 26 elite junior male basketball and soccer players over a 6-week training period. The researchers divided the subjects into two groups. One group performed 4 sets of 6 repetitions (greater fatigue) of the bench press while the other group performed 8 sets of 3 repetitions (lesser fatigue). The increases in power at 20, 40 and 60kg bench press loads in the greater and lesser fatigue groups were similar (6.7 vs. 6.0%, 6.7 vs. 5.8%, and 10.9 vs. 7.2%). Thus, there was a slight non-significant trend for the greater fatigue group to improve upper body power to a greater extent.

In summary, gains in muscular power appear to be enhanced by training closer to muscular failure, although there are only a limited number of studies available in this area.

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What is the effect of rest period duration?

The following studies have assessed how rest period duration affects gains in muscular power. For a refresher, read more about how rest period duration affects gains in muscular size and about how rest period duration affects gains in muscular strength in previous reviews.

Robinson (1995compared the effects of a 5-week, high-volume resistance-training program with three different rest interval durations on increases in power and maximum strength. They recruited 33 resistance-trained young male subjects and allocated them into 3 training groups who performed the same training program except that a long-rest group used a rest period of 3 minutes, a moderate-rest group used a rest period of 1.5 minutes and a short-rest group used a rest period of 30 seconds. Before and after the 5-week intervention, the researchers measured vertical jump height and associated power output. However, power output did not increase significantly in any group. There was a non-significant trend for the long-rest group to display a larger increase in vertical jump power output than the short-rest group (3.1% vs. -1.5%).

Pincivero (1997compared the effects of a 4-week, isokinetic resistance-training program with two different rest interval durations on increases in muscular power. The researchers recruited 15, college-aged individuals and allocated them to either a short rest group (40 seconds) or a long rest group (160 seconds). The training intervention involved unilateral lower body isokinetic resistance-training, 3 days per week for 4 weeks. The researchers found significantly greater increases in isokinetic average power at 180 degrees/second in the long-rest group compared to the short-rest group.

Pincivero (2004compared the effects of different rest intervals on lower body strength and fatigue following a 6-week period of high-intensity resistance-training. They recruited 15 healthy males and allocated them to one of three groups, a short-rest group (40 seconds), a long-rest group (160 seconds), and a control group. The training groups performed isokinetic knee extension exercises at 180 degrees/s, 2 days per week for 6 weeks. Before and after the intervention, the researchers measured isokinetic knee extension torque, work and power at 180 degrees/s. There was no change in power output in any of the groups as a result of the training intervention. However, the researchers did note that there was a non-significant trend for highest single repetition power output to increase to a greater extent in the long rest group compared to the short rest group (12.7% vs. 9.3%).

In summary, it appears that long rest periods are superior to short rest periods for enhancing gains in muscular power.

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What is the effect of range of motion (ROM)?

The following studies have assessed how ROM affects gains in muscular power. For a refresher, read more about how ROM affects gains in muscular size and about how ROM affects gains in muscular strength in previous reviews.

Weiss (2000) compared the effects of training with either machine-based parallel or quarter squats, 3 times per week for 9 weeks. They recruited 10 male and 8 female subjects who were untrained and allocated them to one of three groups: deep squats, shallow squats and a control group. The deep squat group performed deep squats and full ROM leg presses. The shallow squat group performed shallow squats and partial ROM leg presses. The researchers found that their measure of squat power (moderately fast-velocity relative peak–squatting power at 1.43m/s) was not significantly different between any of the three groups.

In summary, there is limited evidence to indicate how range-of-motion affects increases in muscular power output.

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How can we summarize these findings?

The literature describing how different training variables during conventional (non-ballistic) heavy-load resistance-training affect gains in muscular power is clearly limited. However, we can draw some tentative conclusions from the long-term training literature, as follows:

Relative load – studies show that muscular power can be enhanced by a wide range of loads during resistance-training. The literature is conflicting regarding which relative load is best, despite current beliefs that low relative loads are necessary.

Relative load – muscular power is developed in a way that is maximized at the load used during training. Thus, low training loads will likely maximize muscular power most in tests using low loads and high training loads will maximize muscular power most in tests using high loads.

Repetition speed – gains in muscular power are likely enhanced by training at higher velocities rather than at low velocities, where relative load is maintained the same.

Proximity to failure – gains in muscular power appear to be enhanced by training closer to muscular failure.

Rest periods – it appears that long rest periods are superior to short rest periods for enhancing gains in muscular power.

On the other hand, for frequency, volume, range-of-motion, and muscle action, the literature is very limited. It is therefore too hard to say based on the current long-term training literature how these training variables should be programed in order to create the largest possible gains in muscular power.

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What are the practical implications?

For maximizing muscular power during conventional (heavy-load) resistance-training, it seems best to train with a range of relative loads, to emphasize the relative load most relevant to the sport being trained for, to use faster repetition speeds, to use long rest periods, and to train closer to muscular failure (subject to the ability to recover from workouts appropriately).

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