Does stretching really help?

Many people stretch when they exercise or play sport. Others don’t stretch but feel they should. And some people don’t see any reason to stretch at all.

The reasons for stretching are diverse. Most people think stretching makes them more flexible. Some believe stretching reduces risk of injury, reduces soreness experienced after exercise, or enhances sporting performance. Optimists think stretching does all these things.

But do we really need to stretch when we exercise? And does stretching increase flexibility, reduce the risk of injury, reduce soreness and enhance sporting performance? The answer is neither yes nor no.

Randomised trials
The only way researchers can get a really clear idea of the effects of stretching is to conduct randomised trials.

In randomised trials, a lottery is used to allocate each participant to either receive the treatment (in this case, stretching) or not. Then the outcomes (injury, muscle soreness or sporting performance) of the trial participants who stretched are compared with the outcomes of those who didn’t. The difference in the outcomes of the two groups tells us about the effects of stretching.

The first two trials of the effects of stretching on risk of injury, conducted on 2,631 army recruits, showed three months of routine stretching before exercise didn’t appreciably reduce injury risk. A more recent trial on 2,377 recreationally active people had very similar findings: three months of regular stretching had little or no effect on risk.

Together, these trials strongly suggest stretching doesn’t appreciably reduce injury risk.

A number of other randomised trials have investigated the effects of stretching before and after physical activity on the soreness experienced after exercise. They suggest stretching does reduce soreness, but the effect is very small.

A review of such trials concluded that: muscle stretching, whether conducted before, after, or before and after exercise, does not produce clinically important reductions in delayed-onset muscle soreness in healthy adults.

Flexibility and strength
The effect of stretching on sporting performance is less clear, or at least more complex.

Few randomised trials have measured sporting performance as an outcome. Instead, most have studied the effect of stretching on two intermediaries that are likely to affect sporting performance: flexibility and the ability of muscles to generate force. To understand the effects of stretching on flexibility and muscle force generation, it’s necessary to distinguish its acute and chronic effects. Acute effects manifest immediately after a stretch whereas chronic effects manifest only after repeated bouts of stretching, perhaps over months or years.

Stretching acutely increases flexibility: After just a few seconds or a few minutes of stretching, joints move further and resist movement less. But this effect is really just transient. Once the stretching stops, flexibility returns to pre-stretch levels. And recovery is largely complete within a few minutes of finishing the stretch.

It’s possible, but less certain, that stretching also has chronic effects on flexibility. Regular stretching could stimulate adaptations of muscles and other tissues that bring about lasting increases in flexibility.

Everyday observations suggest that’s true, because ballet dancers and yoga teachers, who stretch a lot, tend to be more flexible than the rest of us.

But, while it seems obvious that regular stretching makes people more flexible, it has proved remarkably difficult to demonstrate that in controlled experiments.

www.theconversation.com