"We could not find a benefit," said Stephen B. Thacker, director of the epidemiology program office at the Centers for Disease Control and Prevention. Athletes who stretch might feel more limber, but they shouldn't count on stretching to keep them healthy, he said.

Thacker and four CDC colleagues combed research databases for studies that had compared stretching with other ways to prevent training injuries. They combined data from five studies so they could look more closely for any benefits that might emerge as a pattern. Their report is in the March issue of the American College of Sports Medicine journal, Medicine and Science in Sports and Exercise.

People who stretched were no more or less likely to suffer injuries such as pulled muscles, which the increased flexibility that results from stretching is supposed to prevent, researchers found. And the injuries found in the study typically happened within the muscle's normal range of motion, so stretching them would not have made a difference, Thacker said.

Other research has found that warm-ups, which increase blood flow through the muscle and make it more ready to respond to exercise, can reduce the risk of injury, Thacker said. Being in good shape also helps. Strength and balance training reduced injuries as well, he said.

People such as gymnasts and dancers might be exceptions, because their activities require great flexibility, so stretching might improve their performance, Thacker said.

In case future research does find a benefit, Thacker has no problem with athletes continuing to do gentle stretching. That's not the case with stretches that include sudden fast movements, called "ballistic stretches," which have been found in other studies to raise injury risks.

The study's findings make sense, said Mike Bracko, director of the Institute for Hockey Research in Calgary. "We have done some work with hockey players showing flexibility is not an important variable," he said.

A strain typically happens when a muscle has to react suddenly to control an athlete's movement, Bracko said. An example would be a tear in a muscle in the back of a sprinter's leg as it contracts to keep the muscles in the front of the leg from moving the knee too far forward, he said.

Two other researchers said, however, that there may still be value in the stretches that coaches require, and athletes do.

Lynn Millar, a professor of physical therapy at Andrews University in Berrien Springs, Mich., said her experience in treating people with injuries tells her that those who don't stretch may find they can't move their arms and legs as far as they used to, and this could set them up for injury.

"Unfortunately, a lot of us don't have a normal range of motion," Millar said.

Stephen Rice, director of the sports medicine center at Jersey Shore University Medical Center in Neptune, N.J., said he values the experience of trainers and athletes.

Flexibility is an element of fitness, and stretching ought to make a person more flexible, Rice said. "I would say the conventional wisdom has a certain amount of wisdom to it," he added.