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Dangers of Stretching

By August 1, 2017March 4th, 2021Exercise, Lifestyle & Stress
Athlete Stretching

Over the years research has shown again and again that stretching does not prevent injury and won’t help endurance performance — but it can cause harm.

Runners, cyclists, swimmers, and other athletes use various types of static stretching routines, and sports medicine professionals, and coaches often recommend stretching, too.

Unfortunately, most are doing so out of tradition rather than from any scientific basis.

For many years, professionals who opposed stretching have argued that stretching does not reduce the risk of injury or improve athletic performance,  and that it can contribute to injury and reduce performance. Those opposed to stretching have relied on two different perspectives in which to make their claims.

The first perspective is a clinical one. This includes physical findings whereby a muscle’s function is shown to diminish after it’s stretched. Other observations are made as well – take a group of athletes divided into stretchers and non-stretchers, and many more injuries will be found in the first group.

I first learned about the dangers of stretching in the mid 1970s, and by the early 1980s. As I gained more experience treating and training athletes, I developed an even better clinical perspective. By that time I had many hundreds of athletes to compare. The results were that in those who were injured a significant number were regular stretchers. Meanwhile, among athletes who did not stretch, injury rates were significantly lower.

While these were simply my own observations, many in sports medicine who recommended stretching often claimed they had the opposite perspective — stretching helped athletes.

Clinicians who evaluated muscle function in athletes observed one outstanding factor — stretching a muscle could make it longer (the reason it increases flexibility), and this resulted in a reduction in function from a loss of power. In other words, stretching caused abnormal inhibition — weakness. There was a consensus on this issue by many, although certainly not all, clinicians.

Despite these notions, the tradition of stretching became a difficult one to break for millions of athletes — it’s as ritualistic as reading the new running shoe reviews. It often starts in young athletes who are encouraged by coaches to stretch to reduce injuries.

Trying to rationalize against strong tradition was not easy. I often used a common example of the increased injury rate in stretchers versus non-stretchers regarding the hamstring muscles. It is both the most frequently injured muscle group and the most stretched. Studies now show that stretching does not make tight hamstrings less stiff.

The decade of the 80s saw a dramatic rise in the number of recreational runners, along with the new endurance sport of triathlon. Combined with more athletes on university and college campuses, researchers had what they needed: more subjects for research. Studies began appearing that showed stretching not only did not reduce injuries or improve performance, but could actually do the opposite.

This was the start of the much-needed second perspective — published research. It continues today. For the most part, these carefully conducted human studies have shown that stretching decreases a muscle’s force production capacity — in other words it causes weakness. This and other unhealthy side effects of stretching have been demonstrated in various muscle-function tests using electromyographic, dynamometer, mechanomyographic, and similar devices commonly used in human research.

One particular study, conducted by J. Cramer and colleagues from the Department of Kinesiology at the University of Texas, compared changes in muscles that were stretched and not stretched in the same person. It concluded that stretching one muscle can also impair another muscle that was not stretched, possibly through a central nervous system inhibitory mechanism. In other words, by weakening a muscle through stretching, the brain and spinal cord may trigger other muscles that are not stretched to become weak as well. This may occur, for example, even in muscles in the left leg when those in the right leg are stretched.

Other studies demonstrated adverse effects on lower limb power, sprinting ability, vertical jump and aerobic endurance training. Despite these studies, the tradition of stretching continues in power sports, track and field, basketball and endurance sports.

While the studies show that these abnormal changes induced in a stretched muscle can last for an hour, some clinicians have demonstrated that stretching can cause prolonged muscle problems that can last days and even weeks.

As studies on stretching increased over the years, another type of evaluation — one that assesses a large group of studies and the subjects used for them — was performed. Ian Shrier, M.D., a past president of the Canadian Society of Sports Medicine, published such a study in the Clinical Journal of Sports Medicine in 1999 titled “Stretching Before Exercise Does Not Reduce the Risk of Local Muscle Injury.” Among his conclusions were that stretching can produce damage in muscles, and that stretching can mask muscle pain.

An important issue almost got lost in what sometimes became a heated debate. There were few, if any, published studies that consistently demonstrated that stretching reduced injuries or improved endurance performance — the two main reasons given for stretching.

Confusion arises when a study shows that ranges of motion or flexibility improve with stretching. This has been shown by some studies. However, increased range of motion at what cost? These studies don’t address an important question. One problem caused by stretching is that muscles become too loose — weaker — allowing the associated joint to move in a wider range of motion. This increased range of motion/flexibility puts more stress on the joint, which is no longer supported properly by the muscle, increasing the risk of injury.

Damaging a muscle through any means, including stretching, will obviously have an adverse effect on an athlete’s gait. The loss of smooth, efficient movement puts stress on virtually all other structures — ligaments, tendons, joints and bones, in addition to many muscles. The body tries to compensate for this irregular movement, and in doing so uses up more energy, taking away from one’s performance. A recent study by Jacob Wilson and colleagues from Florida State University showed how stretching can result in poor running economy, increasing energy consumption during an endurance event, and decreasing performance.

My recommendation has always been to include an active, aerobic warm up as part of each workout or race. This can be accomplished through slow running, biking, swimming or any aerobic activity that last at least 12-15 minutes. In addition to improving oxygen utilization, lung capacity and fat-burning, it increases flexibility in a safe way. Stretching cannot do the same.

With increased awareness and scientific knowledge, more athletes, sports medicine professionals and coaches are quietly changing sides in the stretching vs. non-stretching debate. We welcome them.


Partial Bibliography

  • Bacurau RF et al. Acute effect of a ballistic and a static stretching exercise bout on flexibility and maximal strength 2009 J Strength Cond Res 23: 304-8.
  • Cramer JT et al. The acute effects of static stretching on peak torque, mean power output, electromyography, and mechanomyography. Eur J Appl Phsiol 2005;93(5-6): 530-9.
  • Kubo, K, Kanehisa, H, and Fukunaga, T. Is passive stiffness in human muscles related to the elasticity of tendon structures? Eur J Appl Physiol 2001;85: 226-32.
  • Nelson AG et al. Acute effects of passive muscle stretching on sprint performance. J Sports Sci 2005;23: 449-54.
  • Wilson, Jacob M et al. Effects of Static Stretching on Energy Cost and Running Endurance Performance. J Strength Cond Res 2010;24 (9): 2274-79.
  • Young, W and Elliott, S. Acute effects of static stretching, proprioceptive neuromuscular facilitation stretching, and maximum voluntary contractions on explosive force production and jumping performance. Res Q Exerc Sport 2001;72: 273-9.