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What causes the muscle cramps in my legs?

Lack of good research on cramps has caused a lot of myths. Let's start with the facts.

Muscle cramps are very common during (and more commonly after) exercise. Several theories try to explain why cramps happen, including low blood sugar, dehydration, salt imbalances caused by sweating and either extreme heat or extreme cold. All these can cause cramping by themselves, but it is not clear if any are the culprit behind normal exercise-induced cramps.

Current theory in sports science literature (current as of 1997) says that skeletal muscle cramps during exercise probably happen when repeatedly stimulating muscles that are shortened (for example, a calf muscle when the toe is pointed). This can happen if the foot is extended (toe pointed) and you try to extend it further. It appears the muscle gets fatigued and doesn't relax well. A reflex arc (the muscle, the nerves that carry signals to the central nervous system and the nerves that carry signals from the central nervous system back to the muscle) keeps carrying contraction signals from the muscle and back to it. This seems to lead to a sustained contraction of the muscle—in other words, a cramp.

Stretching (for this type of cramp, grabbing your toe and stretching the calf) is just about the only thing that stops this "reflex arc signal" and ends the cramp (at least in exercise-induced cases). The muscle, however, is still fatigued. The cramp process is easy to re-trigger unless you rest the muscle for a while. The fatigue-cramp process usually happens most often in muscles that cross two joints. The calf muscle, for example, crosses the knee and ankle. At those points, the muscle is easy to shorten and continue contracting.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.