Dynamic Stretching Beats Static Stretching for Team Sports

Introduction
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.

Method
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

Results

• 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.

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.

Method
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.

Results

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.

Complex, Specific Training Improves Sports Performance

Introduction
It is much more difficult to improve the physical performance of highly trained athletes than of previously untrained subjects. Thus, it is noteworthy that the study described below by Alves et al. (Journal of Strength and Conditioning Research, vol 24, no 4, pages 936-941, 2010) produced significant performance improvement among elite young Portugese soccer players using brief exercise sessions once or twice per week.

Experimental Method
23 young elite soccer players underwent the following tests before and after an 8-week period:

• vertical jump from a static, bent-knee position
• vertical jump using a dynamic countermovement (natural quick knee bend)
• 5 meter sprint
• 15 meter sprint
• soccer agility test

All subject initially did 2 weeks of general weight training before being divided into 3 experimental groups that did the following for 6 weeks in addition to their normal soccer training:

Group 1 - Once a week, before their regular soccer training session, they went through the following 3 exercise stations:

1. 6 reps of squats with 85% of max weight, 5 meters of high-knee skipping, 5 meter sprint
2. 6 reps of calf raises with 90% of max weight, 8 vertical jumps, 3 soccer-ball high-head hits
3. 6 reps of knee extension with 80% of max weight, 6 jumps from seated position, 3 60-cm drop jumps

Group 2 - The same routine as Group 1, but done twice a week instead of once a week.

Group 3 - Control group - did no exercises supplementary to their regular soccer practice.

Results:
5-meter sprint time improved 9% for Group 1 and 6% for Group 2
15-meter sprint time improved 7% for Group 1 and 3% for Group 2
vertical jump from static bent-knee position improved 13% for Group 1 and 10% for Group 2
none of the groups improved significantly in the countermovement jumps or agility test
the control group did not improve in any of the tests

Conclusions
A relatively short exercise program of weight-lifting, jumping, and sport-specific movements performed once or twice per week can significantly improve the physical performance of elite athletes. Even though the results of the once per week and twice per week exercise groups did not differ significantly, it appears that the subjects responded better to doing the program once per week rather than twice per week when regular sport training was persued concurrently.

Static Stretching Reduces Jumping Power

Introduction
In static stretching, a muscle is stretched to the point of mild discomfort and the position is held for 15 sec or more. In contrast, dynamic stretching involves rapidly moving in and out of the stretched position. The former recommendation in favor of static stretching was based on the finding that it was effective for lasting improvements in flexibility. Thus, for many years, pre-competition static stretching was widely recommended for a broad range of athletes. However, recent studies, such as the one described below, have shown that static stretching before athletic efforts requiring explosive power (e.g. sprinting and jumping) actually hurts performance.

Study Methods
In a study by La Torre et al. (Journal of Strength and Conditioning Research, vol 24, no 3, pages 687-694, 2010), 17 young men performed vertical squat jumps from a force-detecting platform using various starting knee angles. On one day, they did the jumps after performing static stretches of their quadriceps and calf muscles for 10 minutes. Each muscle was stretched on both legs using 4 sets of 30-second holds with 30-second rests between sets. On another day they did the jumps without stretching beforehand.

Results
At all starting knee angles, stretching before the jump test reduced jump height, peak force, and maximal acceleration, but only the differences for jumps beginning with the knees least bent were statistically significant. When starting the jump with the knees flexed 50 degrees (about a half-squat position) jump height, peak force, and maximum acceleration were respectively 21%, 9%, and 15% lower when stretching was performed first than when no stretching was performed.

Bottom Line 
This study reinforces other ones showing that static stretching prior to an athletic event reduces explosive muscular power. The fact that the negative effect is most pronounced when the knees are only bent to a moderate degree is highly relevant to sports activities because most sports do not involve deeply bending the knee. Dynamic stretching does not have the same detrimental effect. Thus, it appears that before athletic events that require power but not great flexibility it is best to warm up thoroughly and perform dynamic stretches before the event. The detrimental effect of static stretching on muscular power has not been shown to carry over to the following day. Therefore, static stretching may be performed after an athletic event to promote general flexibility without harming physical performance.

Improving Performance in High-Level Athletes

Introduction
     It is not difficult to improve the physical performance of people who have had little or no intense training. Yet, it is much more challenging to improve the performance of high-level athletes who presumably have been training and competing at intense levels for considerable time. After all, their training and play have already stimulated their bodies to make major physiological changes, and many have likely reached a plateau by which they are no longer improving in their physical performance. However, a study by Wong et al. in the latest issue of the Journal of Strength and Conditioning Research (vol 24, no 3, 2010, pp. 653-660) shows that even the performance of professional athletes can be improved by a well-designed training program.

Experimental Methods
A group of Hong Kong professional soccer players were divided into 2 groups that trained for 8 weeks during the pre-season as follows:

• Group 1: made up of 20 players who engaged in strength training and high-intensity interval training twice per week in addition to their regular soccer training. The strength training consisted of 4 sets of 6 repetitions of high pull, jump squat, bench press, back half squat, and chin-up. The high-intensity intervals consisted of sixteen 15-second sprints at 20% faster than maximal aerobic speed interspersed with 15-second rest periods. The method for determining maximal aerobic speed was not clearly described. However, it might be taken as the fastest pace at which one can run 3-5 miles (5-8 km).
• Group 2: made up of 19 players engaged in only their regular soccer training.

Results
Only Group 1 improved significantly in the vertical jump (by 4%), 10-meter sprint time (by 6%), and 30-meter sprint time (by 3%).
Group 1 improved twice as much (20%) in a test of shuttle-running at progressively increasing speed as Group 2 (9%).

Bottom Line
Even high-level athletes can improve their physical performance by following a well-designed training program. Twice per week sessions of high-intensity interval training and weight training in addition to regular sport training appear effective for high-level athletes. It should be noted that this was pre-season training. Generally, during a competitive season, exercise other than regular sport-drills and competition is cut back considerably to avoid overtraining.

Medical Disclaimer
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.

Dynamic Stretching Proves Best For Jump Training

Introduction
For many years, static stretching was recommended as superior to dynamic stretching for improvement of flexibility. Static stretching involves slowly stretching a muscle to the point of mild discomfort, then holding the position for 15 or more seconds. Dynamic stretching involves moving the body into and immediately out of the stretched position, repeating the cycle for several repetitions. However, while static stretching may be more effective than dynamic stretching for improving range of motion, static stretching performed immediately before explosive activities (e.g. jumping, sprinting) has been found to impair performance.

Experimental Procedure
A study by Hough, Ross, and Howatson, described in the Journal of Strength and Conditioning Research (vol 23, no 2, 2009, pages 507-512) compared the effects of static vs. dynamic stretching on jump performance immediately after stretching. Eleven college-age males jumped on different days after either 1) not stretching, 2) performing static stretching, or 3) performing dynamic stretching. The stretching routines both targeted the ankle extensors (calf), hip extensors (butt), hamstrings (rear thigh), hip flexors (front thigh-torso junction), and quadriceps (front thigh). On the static stretch day, someone held the subjects' limbs in each stretch position for 30 seconds. On the dynamic stretch day, the subjects moved into and out of each stretched position 5 times slowly and 5 time quickly, without bouncing. Jump testing (3 max height jumps from a self-selected bent-knee position) was performed 2 minutes after the stretching.

Experimental Results
There were significant differences in jump height between all 3 stretching conditions. After static stretching, the subjects jumped 4.2% less vertical distance than when they didn't stretch at all. However, after dynamic stretching, the subjects jumped 4.9% greater distance than when they didn't stretch. The static stretching did not decrease muscle electrical activity, so its detrimental effect may be due to reduced muscle stiffness. However, the dynamic stretching increased muscle electrical activity, which may account for its positive effect on jump performance.

Bottom Line
Performance of explosive activities like jumping and sprinting can be enhanced by dynamic stretching immediately before the activity. Yet static stretching detracts from explosive performance.

Note
Other research has shown that the negative effect of static stretching on explosive performance is short-term. Therefore, because static stretching is effective for improving flexibility, it can safely be performed following athletic performance or exercise routines without interfering with the following day's athletic performance. This is particularly relevant to sports like gymnastics, that require great flexibility .

A Recent Study on Plyometric Exercise

A recent article in the Journal of Strength and Conditioning Research (Volume 23, no. 2, 2009, pages 495-506) analyzed the combined results of 56 studies of plyometric (bounce) training to determine what exercises were most effective in improving jump height. Increases in the neighborhood of 7% were observed after good plyometric training programs. The combination of squat jumps (jumping up from a static squatting position), countermovement jumps (starting from a standing position, then quickly dipping into a bent-knee position before jumping up) and drop jumps (jumping down to the ground from a box, then jumping up) provided the most improvement in jump height. Adding weight to the body using a vest or other means was not better than jumping with bodyweight alone. Also, weight training in combination with plometric exercise did not result in more improvement than plyometrics alone. Programs of 10 or more weeks were more effective than shorter programs. Programs of more than 20 total sessions of 50+ jumps per session were better than shorter programs of lower volume. Box height (e.g. 6" vs 12") for drop jumps didn't matter. The most experienced athletes improved the most. Improvement was seen even in subjects of low initial fitness level.

A word of caution is in order. Most of the subjects in these studies were of college age and many had been physically active before their studies. Plyometric exercise can result in high forces on muscles and tendons, and injury risk is higher than with slow, steady exercises. Plyometric programs should only begin at a very low level, particularly for those people who have been relatively inactive and those above 35 years of age. More gentle plyometric exercises for the beginner include gentle, submaximal hops and jumps. Running itself is a plyometric exercise, especially when running faster in short intervals interspersed with walking or jogging. Tendons and ligaments take a very long time to build up strength, much more than muscles do, so patience is the key word. The intensity and volume of plyometric workouts should only be increased very gradually, and more advanced exercises, like drop jumps, should only be added after a relatively high jump-strength level is attained.