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Friday, October 29, 2010

Dynamic Stretching Beats Static Stretching for Team Sports

Static stretching involves attaining a stretch to the point of mild discomfort and holding the position for at least 10 seconds. Dynamic stretching involves rapid repeated alternation between a stretched and a relaxed position.

A recent article by Amiri-Khorasani et al. in the Journal of Strength and Conditioning Research (vol. 24, no. 10, pp. 2698-2704, 2010) showed that static stretching detracts from performance on a physical agility test, while dynamic stretching tends to improve it.

Nineteen professional soccer players were divided into more-experienced and less-experienced subgroups. Their performance on an agility test, which involved 14-15 seconds of changing direction and zigzagging as fast as possible around a number of cones, was tested after each of the following:
  • No stretching
  • Static stretching
  • Dynamic stretching
  • Combined static and dynamic stretching
  • The subjects were 4-5% slower after static and combined static/dynamic stretching than they were with either no stretching or dynamic stretching alone.
  • Among the less-experienced players, dynamic stretching resulted in about 3% faster course times than no stretching.
  • Among the more experienced players, there was no difference between the course times after dynamic stretching and no stretching.
Bottom Line
The evidence indicates that dynamic stretching is superior to static stretching for the kind of agility needed for most team sports. This is probably due to a reduction after static stretching in the spring-like stiffness of muscle. The results support those of other studies that have shown a detrimental effect of static stretching on strength, jumping ability and sprint speed. It is not clear why the experienced players in this study showed no advantage of dynamic stretching over no stretching at all. However, since these were professional soccer players, it seems safe to conclude that the effects on amateur athletes would parallel those on the less experienced professional players. Thus, their performance would likely be enhanced by dynamic stretching.

Tuesday, October 26, 2010

Plyometric Training for Improved Sports Performance

Plyometric training has been popular among strength and physical conditioning coaches for a number of years. Yet many people who exercise on their own are not familiar with this method. Simply put, plyometric exercise involved rapid stretch and shortening of a muscle. This occurs in such movements as hopping, jumping, and bouncing. For example, when you jump vertically, you naturally first do a countermovement in which you bend your knees quickly while stretching your quadriceps (front thigh) muscles, then rapidly contract those muscles to straighten the knees and propel the body upwards. Thus, repeated vertical jumps are one kind of plyometric exercise.

There are various gradations of plyometric exercise, and it is considered prudent to start with low-stress ones before progressing to more difficult ones. One of the most stressful plyometric exercises is depth-jumping, in which one jumps down from a box and, after contacting the ground, immediately jumps vertically. This is considered dangerous for anyone who does not already have a strong lower body and has not progressed from low-stress, through moderate-stress, to high-stress plyometric exercise. Various sources have recommended being able to squat with 1.5 times one’s bodyweight before taking on a serious plyometric exercise program. However, it is generally considered safe for people in good health without orthopedic problems to perform low-stress plyometric exercises like low bounces, hops, and jumps.

A recent study by Chelly et al. in the Journal of Strength and Conditioning Research (Vol 24, no. 10, pp. 2670-2676, 2010), showed how effective plyometric training can be.

A group of experienced young male soccer players, average age 19 years, trained as follows:
  • August - preseason training consisting of light resistance exercise and calisthenics
  • September through March (the competitive season) - The players trained 5 days per week for 90 minutes by doing skill and tactical drills along with 30 minutes of continuous play. On one day per week they engaged in a competitive soccer game against another team.
The subjects were divided into 2 groups:

Group 1 only did the training program above.
Group 2 did the training program above plus from January-March they also did the following plyometric training twice per week:
  • Week 1: 5 sets of jumping over ten 40-cm (24“) hurdles spaced 1 meter (39.4”) apart
  • Week 2: 7 sets of jumping over ten 40-cm (24“) hurdles spaced 1 meter (39.4”) apart
  • Week 3: 10 sets of jumping over ten 40-cm (24“) hurdles spaced 1 meter (39.4”) apart
  • Week 4: 5 sets of jumping over ten 60-cm (36“) hurdles spaced 1 meter (39.4”) apart
  • Week 5: 4 sets of depth-jumps from a 40-cm (24“) box
  • Week 6: 4 sets of depth-jumps from a 40-cm (24“) box
  • Week 7: 4 sets of depth-jumps from a 40-cm (24“) box
  • Week 8: 4 sets of depth-jumps from a 40-cm (24“) box

Extensive testing on speed, power, and jump height was performed before and after the training.


The group that did regular soccer training did not show significant improvement in any of the pre-post tests.

The group that did plyometric training in addition to their regular soccer training showed the following statistically significant improvements:
  • Thigh muscle volume: +2.5%
  • Cycle ergometer absolute power: +4.5%
  • Cycle ergometer power relative to body mass: +5.9%
  • Jump height without a countermovement: +8.3%
  • Jump height with a countermovement: +2.5%
  • 40-meter sprint first step velocity: +18.2%
  • 40-meter sprint velocity over first 5 meters: +10.0%
  • 40-meter sprint velocity between 35 and 40 meters: +9.8%

Bottom Line
Although not all studies of plyometric training have produced improvements of this magnitude, it appears that the evidence supports inclusion of plyometric exercise in physical training programs for sports involving sprinting and/or jumping.

NOTE: This description of experimental results is for informational purposes only and does not constitute a recommendation. Anyone engaging in an exercise program should obtain proper medical authorization before doing so.

Monday, October 18, 2010

A Method for Improving Explosive Physical Performance


Post-activation potentiation (PAP) is not a training method. Rather, it is a method for improving performance in an explosive activity (e.g. jumping, sprinting) by doing heavy exercise with relevant muscles (e.g. squats) shortly before the performance. Several studies using either weight-resisted or isometric exercise have shown a positive effect on performance. One such study, by Berning et al. is described in the Journal of Strength and Conditioning Research (vol. 24, no. 9, 2010, pp. 2285-2289).


  • Group 1 - Thirteen trained young men who had been squatting at least twice a week for at least one year.
  • Group 2 - Eight untrained young men
The subjects in both groups were first tested for the maximum amount of weight they could parallel squat for a single repetition. That involved squatting down with a barbell on the shoulders from a standing position until the thighs were parallel to the ground, then standing up again. On other days, each group did the following:
  • On one day they did 5 minutes of low intensity cycling followed by maximal vertical jump testing.
  • On another day they did 5 minutes of low intensity cycling, then a functional isometric squat followed by maximal vertical jump testing. For the functional isometric squat, a barbell containing 1.5 times the subjects’ maximal weight for the parallel squat was placed on supporting rods in a squat rack. A second set of rods was positioned about 4” higher than the first set. The lifter got under the bar so that it rested on his shoulders then drove the bar vertically against the upper set of rods as hard as possible for 3 seconds before placing the bar back to the lower set of rods. The positioning of the rods was such that the subject lifted from a half-squat position. The subjects could lift much more weight than they could in a full squat because of the more advantageous leverage in the half-squat than the full-squat.
  • Among the untrained men, the functional isometric squat performed before the jump test did not provide any advantage.
  • Among the trained men, the functional isometric squat performed before the jump test led to significantly higher jump height, and the effect was retained when they were again tested 5 minutes after the lift. The magnitude of improvement in jumping was about 5% (2.4 cm ~ 1”).
Bottom Line

Post-activation potentiation (PAP) is a phenomenon with a fair degree of experimental support. It can be applied to any athletic activity in which a maximal explosive effort can be conveniently preceded by a heavy squat with a barbell, or even an isometric squat against an immovable object. Such athletic activities include but are not limited to high-jump, long-jump, track sprint, Olympic weightlifting, and Highland Games contests. It remains to be seen if the method can be applied to other athletic activities such as baseball hitting, football kicking, or wrestling. The method does not appear applicable to sports involving exertion over a relatively long period of time such as soccer, basketball, or hockey.

NOTE: This description of experimental results is for informational purposes only and does not constitute a recommendation. Heavy barbell squats should only be performed by experienced lifters. The supportive muscles, tendons, and ligaments involved must be developed using a consistent training program over an extended period of time. Anyone wishing to engage in strenuous physical activity must first determine if it is safe to do so. A physician’s clearance is always the best means of determining if you are healthy enough to exercise. Our exercise risk factor questionnaire can help you estimate your risk.