Exercise-associated Muscle Cramps

author : AMSSM

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Muscle cramps occur in 67% of triathletes. This article discusses several theories on the causes of cramps and what to do if you get one and how to prevent cramps.

By Roy Henderson, MD, MPH

Member AMSSM 

The stats on cramps

Exercise-associated muscle cramps (EAMC) are common in endurance athletes, including triathletes. They tend to occur in exercising muscles during or immediately after exercise, but in some athletes they may occur at other times, such as while sleeping at night.

In one study, 67% of triathletes reported having EAMC, 4% of which were severe. EAMC were most often associated with running (50%), followed by cross-training (20%), biking (15%), and swimming (14%).

Of 162 study participants in a 1989 Ironman, 18% reported never having cramps, 76% had cramps during training, and 62% had cramps associated with racing, more often late in the run.

What causes cramps?

The exact cause of EAMC is not known. Although there are rare medical causes of muscle cramping, these are unlikely to be the cause in an otherwise healthy triathlete. One theory is that cramps are related to dehydration and/or abnormalities in electrolytes, such as sodium, potassium, calcium, and magnesium. Studies looking at this as a cause in distance runners have called this theory into question as an important factor in causing EAMC, at least in endurance athletes.

Another theory is that premature fatigue in exercising muscles leads to increased excitability in the muscle and decreased ability for the muscle to relax, resulting in cramps. Another factor in this theory is poor stretching habits that might result in increased muscle excitability. An interesting part of this theory is that muscles which contract when they are not fully stretched have a harder time relaxing, making them more prone to a cramp. This might help explain why some cramps occur in the calves when you are in bed at night. This usually occurs when the foot is pointing down, and the calf is not fully stretched.

What to do if you get a cramp

The best thing you can do at the time a cramp occurs is to stretch the muscle until the cramp subsides. Better yet, if you feel a cramp coming on, stop exercising immediately and stretch.

Preventing cramps

Typical EAMC should respond to measures designed to minimize premature fatigue in exercising muscles, such as making sure that you are well conditioned for the activities you are demanding from your body; getting adequate sleep; eating a balanced diet, including plenty of fruits, vegetables, and carbohydrates, which are stored in exercising muscle for fuel; and undertaking a regular stretching program of the muscles prone to cramping (a general flexibility program is a good idea).

Occasional cramps are of little concern, but if they occur frequently, keep a log of when cramping occurs in relation to exercise, including the muscle(s) in which the cramps occur, how long the cramps last, and whether stretching of the muscle helps to relieve the cramps. This might help show a relationship between your cramps and your training patterns. If cramps continue on a regular basis, you may need to decrease your training intensity and duration, and you should see your doctor for a closer look at the possible cause of the cramps.

Roy Henderson, MD, MPH
MacNeal Hospital Family Practice Residency
Director, Sports Medicine Fellowship
Berwyn, IL

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date: September 17, 2007