Although stretching is part of the warm-up routine of athletes everywhere, the practice may actually be counterproductive in certain cases, research suggests.

Most people stretch before hitting the court, trail or slopes because they believe that it reduces their odds of injury and boosts their athletic prowess.

There is, however, no clear evidence that a pre-game stretch prevents injuries during the game. And in some instances, stretching right before activity may actually detract from an athlete's performance, according to Dr. Ian Shrier, of the Center for Clinical Epidemiology and Community Studies at SMBD-Jewish General Hospital in Montreal.

Shrier, who is also a past-president of the Canadian Academy of Sport Medicine, reviews the research evidence on stretching in the March issue of The Physician and Sportsmedicine.

The potential downside of stretching, according to Shrier, rests in its immediate, short-term effects, with research showing that it causes a small, temporary reduction in a muscle's force and power.

In the case of an athlete who is already flexible but needs an injection of power in her performance -- greater force in her soccer kick, for example --stretching right before the game may bring no benefit, according to Shrier.

That is not to say, however, that stretching is of no use to athletes.

Stretching is analogous to weight training, Shrier stated. A bout of heavy lifting leads to fatigue and weakness immediately afterward, but if done regularly can build strength over time.

Similarly, Shrier explained, stretching seems to cause mild damage to a muscle that weakens it for a short period afterward. But a routine of regular stretching may help build muscle power and force over time.

One study has suggested that a consistent stretching regimen can improve an athlete's 50-yard dash speed by several hundredths of a second -- a large gain to an elite runner.

Regular stretching, according to Shrier, means stretching on a daily or near-daily basis -- maybe five times a week -- but not immediately before an activity. It's unclear, he said, whether it's better to stretch after exercise or at a different time in the day altogether.

Another difference between a consistent stretching routine and pre-performance stretching is that there is some research evidence that regular stretching helps prevent injuries. Those findings, according to Shrier, come from three small studies, so the injury-prevention benefit is not yet conclusive.

In contrast, studies have generally failed to show that stretching right before an activity reduces the odds of injury.

But even without such a benefit, it's not time to scrap stretching from active people's warm-ups, according to Shrier.

In his review, he details several examples where pre-performance stretching may be a boon-for instance, in the case of a tae kwon do athlete whose high kick reaches greater heights right after stretching.

Similarly, Shrier said that if stretching helps a dancer with the aesthetics of her body form and movement, then stretching before a performance would likely be worth the inch she might lose from her vertical jump due to decreased muscle power.

The definition of "performance," he noted, depends on the activity.

SOURCE: The Physician and Sportsmedicine, March 2005.