Pre-exercise warm-ups may cause more harm than good.
Wisdom immortalized in countless workout tapes and aerobics classes says that limbering up before you exercise helps prevent soreness and injury, but scientists have had a hard time proving it. Epidemiologist Stephen B. Thacker, MD, and his colleagues at the Centers for Disease Control and Prevention reviewed several studies and found that although stretching increases muscle and joint flexibility, there's little evidence that it has any protective effect. Some research even suggests that stretching could be harmful. One study published in the Journal of Strength and Conditioning Research showed that the leg muscles of 14 women were weaker after being stretched.

Although many physiologists still advocate preliminary stretching before a workout, Michael Bracko, PhD, a sports physiologist in Calgary, Alberta, and a spokesperson for the American College of Sports Medicine, agrees with the study's findings: "Muscles get injured because they fail—they're tired or weak, or they have repeated microtraumas—not because they're inflexible," he says. Bracko and Thacker suggest that instead of stretching, you try a new warm-up drill: a light version of the activity you're preparing for—walk before you run, do some easy tennis swings before you start a game. And, Bracko adds, the best way to avoid injuries is to strengthen your muscles with a regular weight training regimen.

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