When it comes to static stretching, research has now repeatedly shown that stretching before exercise is counterproductive and results in a temporary loss of muscle strength. These losses can be as much as 5 percent and are magnified in those that hold a stretch for longer than 45 seconds.
Static stretching may slightly reduce the risk of muscular strains in sports characterized by explosive movement like football, but studies that found this decrease in muscle strain also noticed an increase in ligament sprains and other injuries after stretching.
In addition to the risk of injury, some studies suggest that stretching hurts performance as well—it’s associated with an acute loss in muscular strength. A comprehensive review by Canadian researchers presented in the European Journal of Applied Physiology concluded: “Based on the majority of the literature, it would seem logical to recommend that prolonged static stretching not be performed prior to a high level or competitive athletic or training performance.”
While stretching’s effect on performance seems to be most significant for those that sprint, jump or burst off of starting blocks, negative effects have been found for runners and cyclists as well. It seems that stretched muscles are less efficient, at least for a time, lowering a runner or cyclists’ fuel economy. After a pre-run or pre-cycle stretch, endurance athletes have to work harder to go at the same pace as someone who hasn’t stretched. Notably, in one such experiment, after first either stretching or quietly resting, runners were asked to complete a one-mile run as fast as possible. After stretching the runners ran an average of 13 seconds slower in the mile test.
A plausible explanation for this phenomenon is that stretching may make the muscle more compliant, and could impair its neurologic function. In layman’s terms, like an old rubber band that’s lost its elasticity, a muscle can’t contract as forcefully after it has been stretched.
Of course, there are sports for which muscle flexibility is more important than strength. Stretching to develop flexibility is most useful for those individuals whose sport demands a high degree of motion, like ballet, gymnastics or figure skating, during which participants need to stretch to achieve the required motion for their activity. Shrier agrees, saying, “If you can kick the opponent in the head in a martial arts match with stretching but not without stretching, your performance is increased even though the power behind the kick is less.”
While many recreational fitness enthusiasts might not notice if a run took 45 seconds longer than normal, most sports medicine experts recommend a different pre-exercise activity to replace stretching. For both the weekend warrior and the professional athlete, that activity would be a warm-up. Warming up with a light jog or gentle bike ride, for example, has been shown to enhance subsequent performance.
“I strongly recommend people warm up as they start activity and increase the intensity gradually,” Shrier says. “In general, if they stretch before activity, I suggest they stop and replace it with more warm-up because most people simply do not warm up enough.”
For those who are married to their pre-workout stretch, dynamic stretching, which incorporates more the characteristics of warming-up, uses constant, fluid motion, which doesn’t trigger the same performance deficits as static stretching, in which the end positions are held and sometimes taken to the point of discomfort.
“Before a workout, repetitive movement takes the body through a wide range of motion and primes the muscles for the activity to come,” Rountree says, suggesting some dynamic stretches. “Pre-run, for example, we use lunges to simulate the running stride and prep the muscles; before a tennis match, pulsing in and out of a squat and circling the arms will get you ready to play.”