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 of calcium, sodium, magnesium or potassium ( Medicine & Science in Sports & Exercise, July 2005).
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 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 in one muscle group or straining in a muscle. Of course, competitive athletes will not do this, and they pay for it with muscle cramps.