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.

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.

Regular Stretching Can Increase Weight Training Gains

Introduction
The value of stretching has been somewhat controversial. While there is no doubt that stretching is necessary for athletes whose limbs go through extreme ranges of motion in their sports (e.g. hurdlers, gymnasts) there is little evidence that it benefits other athletes. Regular stretching has not been shown to reduce the incidence of injuries among runners, and static stretching done right before "explosive" activities like jumping and sprinting actually impairs performance (although not next-day performance). However, a recent study by Kokkonen et al. in  the Journal of Strength and Conditioning Research (vol 24, no 2, 2010, pages 502-506) indicates that regular static stretching can actually increase weight training gains, at least for the first several weeks of a training program.

Experimental Procedure
Group 1 - Performed 3 sets of 6 repetitions of knee extension, knee flexion, and
               leg press 3 days per week (Monday, Wednesday, Friday) for 8 weeks
Group 2 - Performed the same weight training routine as Group 1 but also did a stretching
               routine twice a week (Tuesday, Thursday) consisting of 15 stretches for the hamstrings,
               quadriceps, aductors, abductors, external and internal rotators, planter flexors, and dorsiflexors.
               Each stretch was done for 3 sets of 15-second holds with 15 seconds of rest in between sets.

Results
Group 1 improved in knee flexion, knee extension, and leg press max lifts by 12, 14, and 9% respectively, while Group 2 improved 16, 27, and 31% respectively. For the latter 2 lifts, improvement was significantly greater for group 2.

Bottom Line
A static stretching routine performed Tuesdays and Thursdays can increases strength gains obtained from weight training on Mondays, Wednesdays, and Fridays, at least during the first several weeks of a training program.

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 .

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.