If you've ever developed severe muscle cramps during long-term exercise, the odds are that you never found out why it happened. Doctors in South Africa studied triathletes and found that most of the time, the muscles cramps were not caused by dehydration, thyroid disease, blocked blood flow, nerve damage, or mineral abnormalities in the levels of calcium, sodium, magnesium or potassium (Medicine & Science in Sports & Exercise, July 2005). Probably the most common cause of cramps in exercisers is lack of salt, but this was not shown to be the cause of severe cramps in the elite athletes.

The athletes with cramps had normal electrolytes and did not lose more fluid during exercise than those who did not suffer cramps. The researchers showed that the most likely cause is muscle fatigue or tearing of the muscle itself. Electromyograph (EMG) studies at one to five minutes, but not at ten minutes, showed markedly elevated electrical activity of the nerves controlling the cramped muscles. Therefore muscle cramps during long distance athletic events appeared to be caused by exercise-induced damage to the muscles themselves.

If this is true, muscle cramps during endurance events can be prevented by slowing down when you feel excessive soreness on one muscle group or a straining in the muscle. Of course, competitive athletes do not do this, and they pay for it with muscle cramps.

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.