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For generations, students were taught to stretch before playing games. Then the practice fell out of favor. Studies seemed to show that such stretching temporarily reduces muscular power, weakens athletic performance and increases the risk of injury. So most fitness experts currently advise against stretches before exercise. But now a new research indicates that they might not be such a bad idea after all.

This month, the journal, Applied Physiology, Nutrition and Metabolism (APNM), published a study by four distinguished exercise scientists who analyzed more than 200 studies of how stretching affects the following exercise. In broad terms, they found that stretching can briefly prevent the ability to generate power. So if you reach for your toes and hold that position, tightening your hamstrings (腿筋), you might not then be able to leap as high or start a dash as forcefully as you don’t stretch.

Those undesirable effects were generally found, however, only if each stretch was held for more than 60 seconds and the subject then immediately became fully active, with no further warm-up. “Outside the lab, most people are unlikely to hold a warm-up stretch for longer than about 30 seconds.” Dr. McHugh, the co-author of the study says. The review found few lasting negative impacts from these short stretches, especially if the volunteers followed that stretching with several minutes of jogging or other basic warm-up movements. In fact, these short stretches turned out to have a positive effect.

Do these findings mean that all the athletes should stretch in advance before a match? “Not necessarily,” Dr. McHugh says, “Runners and cyclists don’t have much risk for acute muscle injuries.” Stretching before these activities is unlikely to protect against injury. Runners and cyclists can adequately warm up by jogging or pedaling lightly. But he suggests that people who play basketball and other ball sports should stretch in advance. Those who haven’t stretched since childhood gym class might want to consider consulting an athletic trainer about the best upper and lower body stretches, particularly for the shoulders and hamstrings.