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Tag Archives: rate of force development

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.

Plyometrics are a popular mode of exercise in the strength and conditioning of athletes. As I have posted elsewhere (see http://wp.me/pZf7K-2x ), different plyometric exercises have different power outputs, ground reaction forces, and rate of force developments. This means that especially with advanced athletes, plyometric exercises have to be selected with this in mind so that they match up with the physical qualities that an athlete is attempting to train.

In the October issue of the Journal of Strength and Conditioning Research, Cappa and Behm compared jumping over hurdles (one-leg and two-leg) with counter-movement jumps (CMJ). The idea behind the study was to investigate and quantify the differences between the various jumps.

The authors studied thirteen male rugby and soccer players over two testing sessions. In the first session, the subjects performed maximal CMJs on a force platform. In the second session, the subjects jumped forward over a series of four hurdles set 50cm apart. A force platform was set up after the second hurdle. Subjects did two-legged jumps and single-legged jumps. For the two-legged jumps, the hurdle height was set at 100%, 120%, 140%, and 160% of maximum CMJ height in a random order. For the single-leg jumps, it was set to 70%, 80%, and 90% of CMJ height in a random order.

The results show differences between two-legged, single-legged, and CMJs:
• Two-legged jumps at between 100% and 140% of CMJ height had a ground contact time of around 185ms. The two-legged jump at 160% had a noticeably longer ground contact time at 210 ms.
• One-legged jumps at all heights had a ground contact time longer than the two-legged jumps, at around 260ms for all heights.
• In terms of force production, the CMJ resulted in around 2100 newtons. Two two-legged hurdle jumps resulted in between 4000 and 4300 newtons, independent of the height (i.e. there was no pattern of increasing or decreasing force production with increasing heights). The single-legged jumps had a force production of around 2400 newtons.
• Rate of force production for the CMJ was around 4600 newtons/second. It decreased as height increased on the two-legged jumps, ranging from 41,000 N/s to 32,000 N/s. For the single-leg jumps the rate of force production was around 14,000 N/s.

It needs to be kept in mind that a specific population was studied and this could effect the results. However, the trends are important when selecting exercises for a strength and conditioning program:
• The shorter two-legged hurdle jumps had a short ground contact time, less than 200 m/s. The one-legged jumps had a longer ground contact time (around 260ms). So, when training for activities with a short ground-contact time (like sprinting), two-legged jumps may be the way to go.
• The two-legged hurdle jumps had a significantly greater force production and rate of force production that the one-legged or the CMJs. Again, this needs to be factored in when selecting exercises.
• The rate for force production was almost 300% greater when comparing two-legged jumps to one-legged and almost 900% greater than the CMJ. This brings into question the value of the CMJ as a conditioning exercise when rate of force development is important.

Cappa, D.F. and Behm, D.G. (2011). Training specificity of hurdle vs. countermovement jump training. Journal of Strength and Conditioning Research, 25(10): 2715-2720.

Earp, et al. had an interesting article in the February issue of the Journal of Strength and Conditioning Research that reinforced something that I had written in an earlier post about plyometrics (http://wp.me/pZf7K-P) which is that different jumps may be applicable to different types of athletic events.  This is something that is really logical, but we rarely practice it with plyometrics.

The authors studied 25 “trained” individuals and looked at how characteristics like muscle fascicle length and pennation angle influences rate of force development on various jumps.  This is an interesting approach because there has been some work showing that pennation angle increases as a result of strength training and that length and angle both impact sprinting speed, but nothing looking at jumping.

Subjects performed 2-3 squat jumps (2 second pause at the bottom), countermovement jumps, and depth jumps (from a 30 cm box) on a force platform, the jumps were also videotaped.

There are some interesting results from this study:

  • Depth jump height > counter movement jump height > squat jump height, like you’d expect.
  • Peak vertical ground reaction force is greatest in depth jumps, then countermovement jumps, then squat jumps.
  • The depth jump had the greatest rate of force development at the 0-10, 10-30, and 30-50 millisecond time periods.
  • No anatomical variable predicted propulsion time for any jump type.
  • For the squat jump a longer Achilles tendon meant a faster rate of force production at the later stages of the jump.
  • For the countermovement jump, gastrocnemius fascicle length predicted rate of force development at the early stages of the jump (i.e. greater fascicle length meant greater rate of force development).
  • There is an intensity-dependent effect of Achilles tendon length on early force production.  Restated, higher intensity jumps requiring a faster rate of force production are more dependent upon Achilles tendon length than lower intensity jumps requiring a slower rate of force development.
  • Length of the muscle fascicles and the Achilles tendon is probably more important because of the “stretch” in the stretch shortening cycle.  Greater length means more stretch which means the ability to store and recover more elastic energy, in theory.

 

Things we don’t know from this study:

  • The “trained” status basically refers to recreational weight training.  Some subjects were former football players.  This means that it is challenging to carry these results over to an athletic population, which means that the usefulness of these results is limited.
  • We do not know how experienced these subjects were with these jumps.  Subjects with more experience (i.e. elite athletes) may have performed very differently.
  • We do not know basic things about these subjects like fast twitch fiber percentage, fiber area, or strength levels.  These are critical variables to successful performance of the jumps and may have impacted the results.  It also limits the applicability of the results to a larger population.

 

Interesting things that we can determine from this study:

  • The different jump types have different rate of force development profiles, which makes them more or less applicable to different athletic events.  For example, an athletic event that requires a RFD over a 0-50 millisecond time period is going to benefit more from a depth jump, one that requires it over 200-300 milliseconds is going to benefit more from a squat jump.
  • Fascicle length and Achilles tendon length may be things to look at for athlete selection, but this requires a great deal more research.

 

Earp. J.E., Kraemer, W.J., Cormie, P., Volek, J.S., Maresh, C.M., Joseph, M., and Newton, R.U. “Influence of muscle-tendon unit structure on rate of force development during the squat, countermovement, and drop jumps.”  Journal of Strength and Conditioning Research, 25(2), 340-347.