For Pure Flexibility, Static Stretching Beats Dynamic Stretching

This blog contains several articles that have shown that static stretching impairs physical performance in jumping, running, and team sports, when the stretching is done immediately prior to the effort. Dynamic stretching has not been shown to cause a similar impairment and may even enhance performance. Yet, this finding does not mean that dynamic stretching is superior to static stretching for all purposes. Indeed, a study published by Covert et al. in the Journal of strength and Conditioning Research (vol. 24, no. 11, pp. 3008-3014, 2010) indicates that static stretching is better for improving pure flexibility.

Study Procedures
Over a 4-week period, 16 men and 16 women, aged 20-27 were randomly divided into the following 3 groups:
Static Stretching: Held a stretched position of the hamstring muscles for 30 seconds 3 times a week
Dynamic Stretching: Got into a stretched position of the hamstring muscles then performed small bounces into and out of that position at a rate of 1 per second for 30 seconds, 3 times a week
Control: Did not stretch
Hamstring flexibility was measured as the number of degrees short of 180 degrees that the knee could be extended to while the subject lay on a table with the thigh in a vertical position. Thus, a smaller number of degrees indicated better flexibility.

Results
The differences between changes in hamstring flexibility among all three groups were statistically significant
The control group declined by a mean of 3.3 degrees in hamstring flexibility
The static stretching group improved a mean of 11.9 degrees in hamstring flexibility
The dynamic stretching group improved a mean of 3.8 degrees in hamstring flexibility

Bottom Line
Either form of stretching improves flexibility. However, static stretching improves flexibility significantly more than does dynamic stretching. For sports in which flexibility in not very important, dynamic stretching is best. However, for sports which require a lot of flexibility (e.g. gymnastics, wrestling, high-hurdles) some static stretching is advisable. But because static stretching impairs performance when done immediately prior to the sport activity, it is best to do such stretching immediately following a training session, when the muscles are well warmed up. The impairment in performance caused by static stretching has not been found to carry over to the following day, so post-exercise static stretching should not impair a subsequent day's performance.

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.

Static Stretching Can Impair Distance Running Performance

At times it can be difficult to find sports science articles that have true relevance to athletes. But here's one that can have real impact. A study by Wilson et al. (Journal of Strength and Conditioning Research, vol 24, no. 9, pp. 2274-2279, 2010) provides strong evidence that static stretching before a distance-running event can impair performance among young, male athletes.

Static stretching involves stretching a muscle to the point of mild discomfort and holding the stretch for 10-30 seconds. We have previously highlighted previous evidence that static stretching can impair jumping performance. It has also been shown to reduce maximal leg-press strength, 20-meter sprint speed, and knee-extension torque. Yet this is the first study to examine the effect of static stretching on endurance performance.

Experimental Procedure
10 male collegiate competitive distance-runners and triathletes who ran at least 20 miles per week and were in excellent aerobic condition were tested on 2 different days, at least a week apart, after the following:

1. 16 minutes of stretching consisting of the following 5 stretches each performed 4 times for 30 seconds of holding:: 1) sit on floor with knees straight and reach with both hands to and beyond the toes, 2) stand with balls of feet on a block, letting bodyweight stretch calves, 3) for both left and right, stand on 1 leg and pull the opposite heel toward the butt 4) for both left and right, lunge deeply, and 5) cross the left leg over the right one, and pull the right thigh towards the torso, repeating for other side
2. Quiet Sitting

After stretching or not stretching, the subjects underwent the following treadmill tests:

1. Run at 65% of maximal aerobic capacity (VO2max) for 30 minutes while energy-cost is measured.
2. After 2 minutes of rest and rehydration, run as far as possible in 30 minutes (subjects could control treadmill speed and see a time display, but not see a speed or distance display).

Experimental Results
On the no-strech day, the athletes performed significantly better as follows:

• They covered an average of 6.0 km in 30 minutes on the no-stretch day compared to 5.8 km on the stretch day
• They required an average of 425 calories on the stretch day vs. 405 calories on the no-stretch day to do the 30-minute submaximal run.

Bottom Line
Static stretching before running hurt the athletes' distance-running performance. After stretching they required more energy to run the same speed in the submaximal test, while in the maximal-distance 30-minute test they were not able to run as far. These differences can easily affect the chance of winning a race. The negative effect of static stretching appears to be due to a reduction in the spring-like stiffness of the leg muscles resulting in lower efficiency. Thus, it does not appear advisable to do static stretching before distance-running events. While dynamic stretching has not been subject to similar testing, it is a possible alternative. The evidence suggests that the best warmup before a distance-running event may be walking followed by jogging followed by short-distance runs at speeds increasing to race-pace.

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.

An Effective Stretch for Hamstring Flexibility

An article in the Journal of Strength and Conditioning Research (Vol. 23, no. 2, 2009, pages 660-667) described the comparison of various hamstring stretching techniques done for 30 seconds, 5 days per week. There were 100 subjects ranging in age from 21 to 57. The most effective stretch over the 8 weeks for lengthening the hamstrings was a straight-leg passive stretch. For this stretch, a protruding corner of a wall, a tall piece of furniture or other object is needed. The subject lies on the floor with the crotch at the corner and, with both knees completely straight, keeps the inner surface of one leg on the floor next to the wall and raises the other leg as close to vertical as possible, resting the heel against the other wall forming the protruding corner. This position is held for 30 seconds. Then the subject repositions to stretch the other leg similarly. In each subsequent session, the subject tries to bring the stretched leg more vertical by getting closer to the wall. The passive stretch was more effective than an active stretch in which the subject's hip flexor muscles, rather than a wall, were used to pull the leg toward vertical.

The study must not have included extremely flexible people like dancers and gymnasts who, while keeping one leg flat on the ground, can easily raise the other straight leg beyond 90 degrees. However, such athletes can hold a passive straight-leg position beyond 90 degrees by either having a partner hold the leg or by using a strap to hold the leg in position themselves.