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.

How to Avoid Weightlifting-Related Shoulder Injuries

Terms used in this article:

• Rotator cuff: Muscles (supraspinatus, infraspinatus, teres minor, subscapularis) that stabilize the shoulder joint and rotate the arm at the shoulder
• Internal shoulder rotation: Standing with your upper arm against your torso with your elbow at a right angle, rotate your upper arm inward until your hand touches your abdomen.
• External shoulder rotation: From the position you just attained by internally rotating your shoulder, rotate your upper arm outward so that your hand moves away from your abdomen, as you would when throwing a Frisbee.
• Trapezius muscle: Extends from the back of your head and neck down your central upper back and serves to raise the shoulders and draw them backwards.
• Range of motion: The number of degrees through which a joint can be rotated.

A recent article by Kolber et al. in the Journal of Strength and Conditioning Research (Vol 24, no 6, pp. 1696-1704, 2010) reviewed existing scientific research articles on shoulder injuries brought on by weightlifting. It noted that 25-35% of people who engage in resistance training sustain an injury severe enough to require medical attention and that 36% of such injuries are to the shoulder. The vulnerability of the shoulder is related to the high number of exercises that involve the shoulder, the great stresses the exercises place on the shoulder, and the unfavorable positions in which some exercises place the shoulder. In addition, many lifters do not warm up properly, select a balanced set of exercises, use proper lifting technique, or modify/eliminate exercises that cause pain. Major muscles are frequently worked to the exclusion of minor ones, leading to muscle imbalances. Shoulder muscles commonly injured include the pectoralis major, biceps, deltoid and rotator cuff group.

The Most Common Signs of Shoulder-Dysfunction Among Weightlifters:

• Reduced internal shoulder rotation range of motion
• Excessive external shoulder rotation range of motion
• Underdeveloped external rotation strength relative to internal rotation strength
• Underdeveloped external rotation strength relative to arm abduction (raising) strength
• Underdeveloped lower trapezius strength relative to upper trapezius strength
• Instability of the anterior (front) shoulder
• Tightness of the posterior (rear) shoulder

Common Pain-Producing Exercises
The following exercises in which the upper arm is raised to the side and parallel to the floor while the forearm is vertical put the shoulder in a fully externally rotated position and are considered hazardous:

• Behind the neck pull-down
• Behind the neck overhead press
• Overhead stack machine press in which the hands move rearward as the weight is lifted

Other exercises, although generally safe, also associated with shoulder pain:

• Bench press
• Incline chest fly
• Supine chest fly
• Dip
• Biceps curl

The following may help to prevent weightlifting-related shoulder injury:

• Discontinue any exercise that causes pain.
• If an exercise hurts, try variations that do not hurt (e.g. bench press with rolled up towel on chest to limit movement).
• Balance every push exercise with a pull exercise in the opposite direction.
• Balance exercises involving major body movements (e.g. bench press, pull-down) with those that stabilize and rotate the shoulder.
• Exercises that strengthen external shoulder rotation are particularly important (e.g. do the external rotation movement described above, resisted by weight stack cable or elastic band).
• Do strength exercises for the lower trapezius (e.g. rowing motions with elbows high and shoulders drawn fully back).
• Do flexibility exercises to increase internal shoulder rotation.
• Do flexibility exercises to stretch the rear shoulder (e.g. Stand with upper arm parallel to the ground. Grip elbow with other hand and pull arm horizontally across the chest).

Vibration Training Can Increase Jump Height

Introduction

Because of evidence supporting their effectiveness for improving strength, flexibility and power, whole body vibration platforms have become increasingly available in fitness centers and athletic training facilities. These platforms generally provide repeated vertical fluctuations at a user-selected rate and amplitude (distance). One study reported that frequencies of 20-30 Hz (cycles per second) produced the greatest gains in flexibility and strength. Amplitude adjustment generally ranges from 1-15 mm (0.04-0.60").

While it is easy to train previously untrained people to increase strength and power, it is more difficult to produce improvement in those already trained. Thus, the study described below provided a challenge to whole-body vibration training.

Experimental Method

In a study by Wyon, Guinan, and Hawkey published in the Journal of Strength and Conditioning Research (vol 24, no 3, pp. 866-870, 2010) 18 female undergraduate dance majors, who were currently engaged in 12-16 hours of dance training per week, were divided into the following two groups that were tested before and after a 6-week experimental period:

Experimental Group: In addition to their normal dance training, these subjects did whole-body vibration training two times a week separated by 2 rest days. The training consisted of twice holding each of the following positions for 30 sec while on a vibration platform set at a frequency of 35 Hz and amplitude of 4 mm (0.16").

     Half-squat with knees pointing outwards
     Right leg leading lunge
     Left leg leading lunge
     Maximal height calf raise
     Forward torso bend (at least 90 degrees) with knees straight

Control Group: In addition to their normal dance training, this group held each of the same positions as the experimental group, but on a stable floor rather than on a vibration platform.

Results

The experimental groups improved 2.3 cm (0.9" or 6%) in their maximal vertical jump, while the control group actually declined by 1.5 cm (0.6" or 4%). This difference was statistically significant.

Bottom Line

Whole-body vibration training appears to hold promise for training athletes and dancers. The experimental training required only 5 minutes twice a week. Because the physical demands on in-season dancers and athletes are great, strength and power training is usually limited to avoid overtraining. However, whole-body vibration training seems to be able to improve performance without excessively stressing the athlete. An added advantage is the previous evidence that such training can improve bone mineral density. Low bone density has been a problem with female dancers and athletes who maintain low bodyfat, such as gymnasts and distance runners.

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 .