It comes out of nowhere - while you're playing tennis, gardening, sitting on the couch or even when you're fast asleep.
Suddenly a muscle gets locked in spasm, it's hard as a rock, and the pain borders on unbearable.
Muscle cramps usually target your legs and can last for a few seconds to 15 minutes or more.
Yet as common as cramps can be, experts don't know exactly what causes most cases.
And there's no solid science on how to best treat them. Here's what we do know:
They're common in summer
That's because when you exert yourself in hot weather, sweat drains your body's fluids, which helps muscles contract and relax; heat also depletes salt and minerals, which may cause a muscle to spasm.
Other possible causes: Inadequate stretching, muscle fatigue or simply holding a position for a prolonged period.
Try massaging it
Step 1 to ease a cramped muscle: Stop whatever activity triggered it.
Then try to gently stretch and massage the muscle, holding it until the cramp stops. Though a review published in the journal Neurology showed stretching - and drinking water, another common remedy - aren't proven treatments, both methods are safe if done in moderation and may ease pain.
The jury is still out on other common treatments, such as taking vitamin B complex or calcium channel blockers, but experts agree quinine - once the drug of choice for treating leg cramps - should be avoided; it hasn't been proven effective and may cause severe side effects.
Ask your doctor
Though most muscle cramps are harmless, some may indicate problems with circulation, nerves, metabolism, medications or nutrition.
If your muscle cramps are severe, frequent, don't improve with simple treatments and seem unrelated to an obvious cause like exercise, check with your doctor.
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