Have you watched football players, sprinters and other athletes warming up and stretching before competitions? Two studies, one from Louisiana State University and one from Liverpool University in England, show that they may be harming their performance (Journal of Sports Science, May 2005).

In the first study, elite college sprinters were timed in 20 meter sprints, with and without prior multiple 30-second stretches of their leg muscles. As was expected, both active and passive stretching slowed them down. Many previous studies show that you cannot lift your maximum weight after a muscle is pulled and stretched. Other studies have failed to show that stretching prevents injuries. This study does not tell you to stop stretching completely because there is solid data to show that stretching makes you a better athlete. Stretching elongates tendons and the longer the tendon, the greater force a muscle can exert around a joint to make you stronger and faster. However, this study suggests that athletes should not stretch before competitions.

The English study shows that warming up limits how far you can run. Runners alternated 30 seconds of very fast runs on a treadmill with 30 seconds of running very slowly until they were exhausted. They tired earlier after having their legs heated passively and also after taking a long warm up run before testing. At ambient temperatures of about 69 degrees Fahrenheit, both active and passive heating raised both muscle and body temperatures, which uses up muscle glycogen faster and tires runners earlier. Since warming up has been shown to help prevent injuries, it may be good idea to warming up before power events of short duration, but not before competitions that last for several hours.

Gabe Mirkin, M.D.

Dr. Gabe Mirkin has been a radio talk show host for 25 years and practicing physician for more than 40 years; he is board certified in Sports Medicine and three other specialties.

Dr. Mirkin's daily features on fitness have been heard on CBS Radio News stations since the 1970's. He has written 16 books including The Sportsmedicine Book, the best-selling book on the subject that has been translated into many languages. His latest book is The Healthy Heart Miracle, published by HarperCollins.

Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. A Boston native, Dr. Mirkin did his residency at the Massachusetts General Hospital. He has served as a Teaching Fellow at Johns Hopkins Medical School, Assistant Professor at the University of Maryland, and Associate Clinical Professor in Pediatrics at the Georgetown University School of Medicine. He has run more than forty marathons and is now a serious tandem bicycle rider with his wife, nutritionist Diana Mirkin.