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Tag Archives: power

De Villarreal et al have a really interesting study in the December issue of the Journal of Strength and Conditioning Research looking at the impact of different exercise protocols on the vertical jump. The authors studied college physical education students using one of five protocols: heavy full-squats, power half squats (i.e. to parallel), weighted counter-movement jumps (CMJ), plyometrics, and a combination of all. Subjects were tested on their vertical jump height and their performance on CMJs with 17kg, 27kg, and 37kg of added resistance.

All training took place 3 times per week for seven weeks:
• Heavy squat group: Gradually increased the resistance over seven weeks while decreasing the volume.
• Power half squat group: Gradually increased the resistance over seven weeks while decreasing the volume. The initial resistance was selected as the resistance that maximized power output, after the first week the resistance was increased each week and leveled out at weeks six and seven.
• Weighted CMJ group: Resistance was selected based upon what maximized power output. Initially the group exercised with 30% less than the amount that maximizes power output, over seven weeks this was increased.
• Plyometric group: sets of five rebound jumps.
• Combined group: Basically combined all the above workouts.

In terms of results:
• All groups increased the heights of their vertical jumps, the heights of their loaded CMJ height at each resistance, and the rate of force development during the loaded CMJs. There were no statistically significant differences between any of the groups.
• There were statistically significant increases in power output during loaded CMJs for the combined group and the weighted CMJ group only. However, all groups increased their power outputs by 3-13% at each resistance after seven weeks of training. So while this may not be statistically significant, it is an increase.

The results are interesting because essentially all the training programs worked. To me the most interesting result in the vertical jump height, the weighted CMJ testing condition isn’t really something that’s going to be duplicated on the field. The authors don’t give us the vertical jump values, only a graph so it is difficult to tease out the improvements in vertical jump. This suggests that heavy squats, squats done explosively, weighted vertical jumps, and plyos all improve vertical jump. The results are also interesting because the group with the greatest volume (the combined group) made the same gains as the other groups.

Now, there are some limitations. First, the subjects were college students. It’s very possible that strength trained athletes would have had different results. Second, the study may not have been long enough to tease out differences between the training programs. Third, all the squats and weighted CMJs are being done in a Smith machine which may impact both adaptations and transferability of the results. Finally, by using weights greater than that which maximized power output (the power squat group) or by using weights less than that which maximized power output (weighted CMJ group) both of these groups may not have made the gains that they could have as a result of the training.

De Villarreal, E.S.S., Izquierdo, M., and Gonzalez-Badillo, J.J. (2011). Enhancing jump performance after combined vs. maximal power, heavy-resistance, and plyometric training alone. Journal of Strength and Conditioning Research, 25(12), 3274-3281.

The power clean is a popular exercise for the strength and conditioning of athletes as well as an assistance exercise in the training of Olympic lifters. The lift uses most of the muscles of the body, is done standing up, must be completed in around a second to be successful, and results in a great deal of power output especially compared to many other (and slower) strength training exercises. For all these reasons, it is popular for the conditioning of athletes.

There are a number of variations of the power clean. It can be performed from the floor (power clean), from blocks (the bar rests on a raised surface), or from the hang (the lifter holds the bar from a static position and then performs the lift).

Comfort et al, in the December issue of the Journal of Strength and Conditioning Research, studied whether a particular variation of the power clean results in a better power output. In their study, they had sixteen male rugby league players perform variations of the power clean with 60% of their 1-RM on a force platform. The variations were the power clean proper, the lift from the hang (knee height), the lift from the hang (mid-thigh level), and the clean pull from mid-thigh. Each lifter did three reps on each lift, with 30 seconds of rest between each lift.

The results are not what I expected:
• Mid-thigh power clean and mid-thigh clean pull had the greatest force output, followed by knee height power clean, followed by the power clean proper (~2800 newtons for mid-thigh power clean versus ~2300 newtons for the power clean).
• The same pattern was true for rate of force development (~15,000 N/s for the mid-thigh power clean versus ~8700 N/S for the power clean).
• The same pattern was true for power output (~3600 Watts for the mid-thigh power clean versus ~2600 Watts for the power clean).
• In all cases, the mid-thigh pull had greater force, RFD, and power values than the mid-thigh clean though there were no statistically significant differences between the two.

This is not the first article from these authors on this (see http://wp.me/pZf7K-3w) for a summary of another article. If it’s true, and if we are seeking to maximize our athletes’ training time, then it suggests that the mid-thigh pulls and cleans may be a better use of our time.

Now, there are some assumptions with these results:
1. The subjects are trained. It’s likely that subjects that are more, or less trained would have responded differently to the testing.
2. 60% is the optimal intensity. The other study performed by the authors on this subject also used 60% of 1-RM as the testing intensity. Some authors have found that peak power occurs at 80% of 1-RM, though there is no statistically significant difference in the ranges of 50%-90% of 1-RM (Cormie et al 2007, Kilduff et al 2007).
3. The subjects have good technique on the lifts. Proper technique may have a huge impact on the outcome of the study. We have now way of knowing the subjects technical mastery of the lifts.

Lastly, it needs to be pointed out that this is not a training study. In other words, we don’t see the impact of focusing on x number of weeks of the mid-thigh lifts versus the power clean on power output and other variables. This would be an interesting route to go with future research.

Comfort, P., Allen, M., and Graham-Smith, P. (2011). Kinetic comparisons during variations of the power clean. Journal of Strength and Conditioning Research, 25(12), 3269-3273.

Cormie, P., McCauley, G.O., Triplett, N.T., and McBride, J.M. (2007). Optimal loading for maximal power output during lower-body resistance exercises. Medicine and Science in Sports and Exercise, 39(2), 340-349.

Kilduff, L.P., Bevan, H., Owen, N., Kingsley, M.I.C., Brunce, P., Bennett, M., and Cunningham, D. (2007). Optimal loading for peak power output during the hang power clean in professional rugby players. International Journal of Sports Physiology and Performance, 2, 260-269.

Kettlebells exploded on the scene a number of years ago and have attained almost cult-like status. They are promoted as a tool to increase strength, hypertrophy, power, core stability, metabolic conditioning, and even cardio-vascular conditioning. Despite the claims, almost no research has been done on this exercise mode. Harrison et al, in the December issue of Strength and Conditioning Journal, have an article that reviews the state of the literature and provides recommendations for the implementation of kettlebells into a strength and conditioning program.

As kettlebells have mass, and as this mass can be increased (i.e. you can always exercise with a heavier kettlebell), they are effective at increasing strength and hypertrophy. It also stands to reason that performing explosive exercises with them will result in an increase in power.

In terms of cardio-vascular and fat-loss benefits, the authors don’t report terribly strong research. For example, there is a study that demonstrated that performing the two-handed swing for twelve minutes increases heart rate, but it is not as stressful as running. They report that research looking at the metabolic cost of using kettlebells is unclear and guilty of comparing apples to oranges (i.e. this means you cannot really draw a conclusion on the effectiveness of kettlebells one way or the other).

At the very least, the authors feel that kettlebells can aid with muscular strength/hypertrophy/power and certainly add some variety and fun to a strength and conditioning program.

With regards to implementation, I feel that the authors make an excellent point when they state that: “Training protocols for kettlebells do not necessarily need to be different from the traditional resistance training protocols…” At the end of the day, if the goal is to increase strength (no matter what training tool is used) then one needs to lift heavy weights, for few repetitions, with full recovery. If the goal is to train power, one needs to focus on being explosive, which means limiting fatigue and allowing full recovery. If the goal is endurance or metabolic conditioning, then the workout will look very different.

I personally have some opinions about technique and kettlebell exercises, especially when we start talking about the Olympic lifts and kettlebells. I’m uncomfortable with the idea of swinging the weights for these lifts, which most places advocate. I still feel that the triple extension motion is very important (if the idea is to train for transferable power). I also think that swinging the weight overhead on the snatch is just asking for trouble.

Harrison, J.S., Schoenfeld, B., and Schoenfeld, M.L. (2011). Application of kettlebells in exercise program design. Strength and Conditioning Journal, 33(6), 86-89.

There has been a debate for a number of years about the effectiveness of the powerlifts (bench press, squat, deadlift) at improving power. The thought has been that while these lifts increase maximal strength, they are performed too slowly to train power adequately. Powerlifting proponents, especially with the advent of training with chains and bands, have argued this is not the case. Swinton et al, in the November issue of the Journal of Strength and Conditioning Research conducted a study looking at the deadlift exercise and came up with some fascinating data on the deadlift that may require that this argument be reevaluated.

The authors had 23 experienced subjects (powerlifters and rugby union athletes) participate in the study. On average, the athletes weighed 107 kilograms and deadlifted 227 kilograms. In other words, these athletes are deadlifting more than twice their body weight.

The athletes performed two testing sessions. During the first session, athletes maxed out on the deadlift. They then performed a single repetition at 30%, 50%, and 70% of their 1-RM at maximal velocity.

During the second session, the athletes performed repetitions at 30%, 50%, and 70% of 1-RM at submaximal velocity. After this, they performed maximal velocity repetitions at 30%, 50%+chains equal to 20% of 1-RM, then 70%+chains equal to 40% of 1-RM. Two repetitions were performed at each weight.

Subjects performed the lift on a force platform and had each lift filmed.

Many of the results are what you’d expect:
• As the weight increased, the velocity of the barbell decreased. The velocity was greatest at the maximal velocity trial with 30%+chains (at 2.2 meters per second).
• For the submaximal velocity trials, peak power increased as the resistance increased. For the maximal velocity trials, it was greatest at the 30%+chain load and decreased as the weights increased. Peak power for the maximal velocity trails was more than double that of the submax trials for every resistance except 70%+chains.
• The acceleration phase for performing the lifts with chains is greater than the submax conditions.

The velocity information is fascinating. These numbers exceed some of the velocities seen in the second pull of the snatch and clean as well as the drive of the jerk exercise. This suggests that the deadlift can be performed in an explosive manner to train for athletic power.

Now, there are some challenges with this study. First, the athletes studied are able to deadlift double bodyweight, which means that they have some skill on the exercise. It’s unclear if the results can be transmitted to other athletes. It is actually likely that there needs to be a strength base present before advanced training tools, like chains, can be effective. Second, the athletes self-selected “submaximal” and “maximal” velocities. Without standardizing the submaximal velocities (i.e. lift at 70% of maximal deadlift velocity, etc.) it makes it difficult to compare the results across lifters and to apply them to a larger pool of athletes. The final limitation that needs to be kept in mind is that this is not a training study. In other words, this study is not looking at the effectiveness of X number of weeks of training the deadlift with chains on power. It’s a snapshot in time and this needs to be kept in perspective when reading about it.

Swinton, P.A., Stewart, A.D., Keogh, J.W.L., Agouris, I., and Lloyd, R. (2011). Kinematic and kinetic analysis of maximal velocity deadlifts performed with and without the inclusion of chain resistance. Journal of Strength and Conditioning Research, 25(11), 3163-3174.

Sprinting is thought to be made up of several qualities; acceleration (the ability to increase velocity), maximum velocity (the fastest an athlete can run), and speed endurance (the ability to maintain velocity). Not all of these qualities are thought to be equally important for every athlete. Outside of sprinters, most athletes don’t have to worry about speed endurance. For most sports, acceleration and maximum velocity will be the most important qualities.

For a 100 meter sprinter, maximum velocity isn’t reached until 60-80 meters. If this holds true for other types of athletes, it suggests that most athletes are in an acceleration situation when sprinting in sports. There is a lot of mixed research on acceleration in the sense that some research shows that maximum strength is important for acceleration, some shows that it is not. Lockie et al in the October issue of the Journal of Strength and Conditioning Research investigated the variables that differentiate field sport athletes with better acceleration from those with slower acceleration.

The athletes were evaluated on 4×10 meter sprints, 3 trials each of five alternate bounds for distance, counter-movement jump, 40cm drop jump, leg stiffness was evaluated, 5 meter sprints over a force platform, and a 3-RM back squat (in a Smith machine) was used to evaluate strength.

The results are interesting:
• The faster group had a higher velocity from 0-5 meters and 0-10 meters.
• Stride length was similar between the faster and slower groups.
• Stride frequency had some differences, though they were not statistically significant. From 0-5 meters, the stride frequency for the faster group was almost 10% faster than the slow group. From 0-10 meters it was almost 7.5% faster than the slower group.
• Both groups exerted a similar amount of force against the ground, but the faster group had a much shorter ground contact time than the slower group.
• There were differences between the faster and slower groups in terms of the strength and power tests. The table below shows how much higher (or lower) in terms of percentage the faster group was when compared to the slower:

  Difference
5 Bound Test

0.055654

Counter-Movement Jump

0.138889

Drop Jump Height

0.222222

3-RM Squat

0.157742

3-RM Squat/Body Weight

0.19685

This study suggests that those field sport athletes who have higher velocities during acceleration may be achieving this due to a number of factors. First, they have a greater stride frequency (i.e. they are moving their limbs more quickly). Second, they are spending less time on the ground. Third, they have greater strength and power. All of these are qualities that are trainable.

This is an interesting study for a number of reasons. First, it uses field sport athletes. Unfortunately, we are not given any information on what level of athlete or what sport, which would be useful. But it is significant because it is likely that studies on elite sprinters probably won’t transfer to a soccer player. Second, it suggests that strength, power, and moving the limbs more quickly is important for acceleration. This is significant because the old school of thought says that we get faster by moving our limbs more quickly (i.e. technique, A drills, etc.). The other school of thought says that we get faster by exerting more force against the ground. This study suggests that both schools of through are correct.

Lockie, R.G., Murphy, A.J., Knight, T.J., and De Jonge, X.A.K.J. (2011). Factors that differentiate acceleration ability in field sport athletes. Journal of Strength and Conditioning Research, 25(10), 2704-2714.

Hansen et al in a September 2011 article in the Journal of Strength and Conditioning Research investigate the ability of force-time and power-time tests to differentiate speed performance and to differentiate the competition level of rugby union players.

The authors studied forty professional rugby players. The athletes were evaluated on their 30m sprint from a standing start (with splits at the 5m, 10m, and 30m marks). They also performed squat jumps on a force platform with 40kg of resistance. These squat jumps were analyzed in terms of their force-time curves and power-time curves.

For the sake of analysis, the authors divided the athletes into fast (30m time 4.23 seconds) and slow (30m time 4.57 seconds) groups. The results are interesting:
• The slower groups produces 1-4% more peak force on the squat jump, but when this is expressed in terms of bodyweight the faster athletes produce 5-9% more peak force/body weight.
• The faster group produces -2 to 5% more peak power on the squat jump than the slower group. In terms of relative peak power, the faster group produces 8-14% more peak power than the slower group.
• The faster group has between 2-7% greater peak velocity (on the squat jump) than the slower group.

It needs to be noted that none of these results were statistically significant.

The junior athletes, when compared to the older ones, were slightly faster at all the time splits. The older athletes had greater peak force, peak power, and peak velocity in terms of absolute and relative measures than the younger athletes.

Because many of these results weren’t statistically significant, it’s difficult for the authors to make the conclusion that they effectively differentiate faster versus slower athletes. But it is also unclear why some a complicated assessment is desirable for rugby athletes especially when a sprinting test does a good job of differentiating faster and slower athletes. Even if there are bad weather periods, sprinting tests can still be done indoors.

Hansen, K.T., Cronin, J.B., Pickering, S.L., and Douglas, L. (2011). Do force-time and power-time measures in a loaded jump squat differentiate between speed performance and playing level in elite and elite junior rugby union players? Journal of Strength and Conditioning Research, 25(9), 2382-2391.

Requena et al had a study published in the August Journal of Strength and Conditioning Research looking at the relationship between back squat strength, ballistic squat performance, vertical jump, and sprint speed.

The authors studied 21 “semiprofessiona;” sprinters (100 and 200 meter sprinters), though we are not given information about their performance on the 100 meter or 200 meter races.

It needs to be pointed out that the squat tests were unusual. Both traditional and ballistic squats were evaluated on a Smith machine. They were also tested having the subjects squat down to 100 degrees of knee flexion, hold it for two seconds, then perform the concentric phase of the lift.

Subjects were also tested on their vertical jump and 80 meters of sprints (with 10 meter splits recorded). These results were then correlated with the 1-RM on the traditional squat as well as maximal peak and average power on both squat tests.

The results are interesting:
• The vertical jump correlated with power values of the ballistic squat but not the 1-RM traditional back squat.
• Power outputs from the ballistic squat were more highly correlated with vertical jump performance than the traditional squat.
• The sprint times correlated with the 1-RM on the traditional squat as well as the power values for both kinds of squats.
• There was a trend for the ballistic squat power outputs to be more strongly correlated with sprint times than traditional squats.

The study is interesting from several standpoints. First, it is using a homogenous group of sprinters. This is both an advantage and a concern. An advantage because the results are very relevant to this population, a concern because the application of the results may be restricted to this population. Second, the relationship (or lack thereof) between vertical jump performance and 1-RM is counter-intuitive. This is something that warrants further study. Third, the trend for ballistic squat performance and vertical jump/sprint performance is interesting and warrants further study. Is this something that would apply more to one group of athletes or one level of ability rather than others?

Requena, B., Garcia, I., Requena, F., de Villarreal, E.S-S., and Cronin, J.B. (2011). Relationship between traditional and ballistic squat exercise with vertical jumping and maximal sprinting. Journal of Strength and Conditioning Research, 25(8), 2193-2204.

Argus et al had a study published in the August Journal of Strength and Conditioning Research looking at the impact of assisted, resisted, and bodyweight vertical jump training on vertical jump height.

The study involved two parts. In the first part, recreational weight trainers performed jumps on a force plate under resisted, assisted, and bodyweight conditions. Resisted involved performing jumps with elastic bands attached from the subject’s waist to the floor (i.e. resistance on the concentric phase of the jump). Assisted involved elastic bands attached from the subject’s waist to the ceiling (helps the subject during the concentric part of the jump). Bodyweight was a normal jump without any kind of assistance or resistance.

This part of the study found that the assisted jumps had the greatest peak vertical velocity and peak power, followed by free jumps, followed by resisted jumps. Peak force was greatest for resisted, followed by bodyweight, followed by assisted jumps.

The second part of the study involved four weeks of contrast training with rugby players. Twice a week they performed a set of four power cleans followed by six jumps under one of the three conditions. At the end of four weeks, the assisted group increased their jump height by almost 7%; the resisted group by almost 5%, the bodyweight group by almost 1.5%.

This is an interesting study because there are diminishing returns with exercise. As we become stronger it becomes more difficult to increase strength. As we become a more advanced athlete, it becomes more difficult to increase power. This study suggests some simple ways to make plyometrics more effective as athletes advance in fitness.

Argus, C.K., Gill, N.D., Keough, J.W.L., Blazevich, A.J., and Hopkins, W.G. (2011). Kinetic and training comparisons between assisted, resisted, and free countermovement jumps. Journal of Strength and Conditioning Research, 25(8), 2219-2227.

Comfort et al published an article in the May issue of the Journal of Strength and Conditioning Research on power clean variations. This is an interesting article because it may have some implications for strength and conditioning practices.

There are many variations to the clean used in strength and conditioning. Probably the most common is the power clean (where the bar is received in a partial squat). The power clean is performed from the floor (called a power clean), or from various “hanging” starting positions (means that the starting position is not from the floor, but the lifter is supporting the weight). Hanging positions include having the barbell start from above the knees, start from knee height, or start from below the knee height.

Normally, the power clean is taught through a series of progressions. First it is taught from above the knees, then the knees, etc. until finally the exercise is being performed from the floor. The thinking is that the from the floor version is the most preferred as the athlete is handling the most weight and generating the most power from that position.

The Comfort et al study casts some doubt on that practice.

They studied eleven elite male rugby athletes. The athletes performed sets of three repetitions with 60% of their 1-RM power clean while standing on a force platform. One set of three was performed with each of the following variations:
• Power clean (floor)
• Hang power clean, knees
• Hang power clean, above the knees
• Hang clean pull, above the knees

The findings are interesting:
• There were significant differences in terms of peak ground reaction forces between the variations. The hang (above the knees) and hang pull both resulted in almost 3000 newtons, whereas the floor and knee variations did not even generate 2500 newtons.
• There were significant differences in terms of rate of force development between the variations. The hang (above the knees) and hang pull both resulted in almost 15,000 N/s whereas the floor and knee variations did not even generate 10,000 N/s.

These results call current practices into question. It’s possible that the hang, above the knee and hang pull may be more beneficial for power output than performing the lift from the floor. This is beneficial in the sense that it is easier to teach these exercises.

Now, some caution needs to be taken with interpretation of these results. It’s possible that the athletes were not using good form on the lifts and this form could have had a major influence on the results. It’s possible that the athletes may not have been very experienced at the knee or floor variations, which would have influenced the results. It’s also possible that these results may only apply to this particular population (i.e. there may be something unique about the combination of their body structure, conditioning background, technique, etc. that caused these results).

This would be an interesting area to see more research on, with a wider subject pool. If the lifts from the hang result in the greatest power outputs and greatest rates of force development, then why waste an athlete’s time performing any other variation?

Comfort, P., Allen, M., and P. Graham-Smith. (2011). Comparisons of peak ground reaction force and rate of force development during variations of the power clean. Journal of Strength and Conditioning Research, 25(5), 1235-1239.

Joel Smith et al had a really interesting study published in the January issue of the Journal of Strength and Conditioning Research looking at depth jumps. They had noticed that the use of a goal (or target) in conjunction with depth jumps increases the height of the jumps and the knee flexor moments. Based on this, their study was meant to determine the differences between a regular depth jump from a 45-cm box, a depth jump from a 45-cm box with an overhead goal, and a depth jump from a 45-cm box over a hurdle.

The hurdle height was set to be individualized and challenging for each athlete. The athletes, prior to the test, determined the highest hurdle they could jump over using a counter-movement jump. For the testing conditions, the hurdles were set to be 5cm lower than that height.

The Vertec was used in a way that when the subjects landed from the depth jump, they attempted to jump as high as possible with that height being recorded by the Vertec.

The authors used Division III male athletes and after a standardized warm-up had them perform 12 depth jumps, four on each condition. The results are interesting:
• Ground contact time: The depth jump hurdle had an almost 25% shorter ground contact time than the other two jumping conditions.
• Vertical velocity at toe off: The regular depth jump had the lowest vertical velocity, the hurdle condition the highest, and the goal jumping condition was in-between. Remember that having a lower velocity is a bad thing in athletics.
• Joint kinematics: In terms of statistically significant results; the hurdle condition resulted in lower knee flexion, knee extension, and hip flexion, and hip extension angles than the other jumping conditions. This has some implications because of how elastic energy works, the greater the joint angles before the jump the more likely some of that elastic energy is going to be dissipated.
• Ground reaction forces: Greater for the hurdle group by 16-17%.
• Moments/power output: Ankle and knee flexor moments were greater for the hurdle group, along with power generation and power absorption. The authors feel this is especially important as they point out that the ankle is the largest power absorber and generator in unilateral power production.

The interesting take-home part of this study is that the depth jump combined with the hurdle may be really valuable for athletes that are in sports that require a short ground contact time. There has been a lot of debate in the track and field literature over the years that a lot of standard exercises and plyometrics have a ground contact time that is too long to adequately transfer for track and field, many authors (the authors of this study as well) point out that short vs. longer contact times are fundamentally different motor skills. An athlete may excel at one but not the other.

This study does have limitations that the reader should be mindful of:
• There’s a skill component to performing depth jumps which could influence the outcome: Athletes with more or less skill will respond differently and may very well score differently than the ones in this study.
• There’s a strength component to performing depth jumps which could influence the outcome: Plyometrics seem to be more effective for stronger athletes, we do not know the strength levels of the athletes in this study.
• The subjects had some challenges with the Vertec jumps: Dropping off the box, rebounding, and jumping up to touch the Vertec takes some skill and this could have had an influence on the results of this group.

Smith, J.P., Kernozek, T.W., Kline, D.E., and Wright, G.A. (2011). “Kinematic and kinetic variations among three depth jump conditions in male NCAA Division III athletes.” Journal of Strength and Conditioning Research, 25(1), 94-102.