A charley horse is a sudden, painful muscle cramp, usually in your leg or foot. The muscle tightens up hard and won't relax, creating a sharp pain that can stop you in your tracks. You might get a charley horse in your calf while swimming, or wake up in the middle of the night with one in your foot.

These cramps often happen when muscles get tired, dehydrated, or stretched in an awkward way. Athletes sometimes get charley horses during games after running hard. The muscle contracts so intensely it can feel like a tight knot under your skin.

When you get a charley horse, gently stretching and massaging the cramped muscle usually helps it relax. Walking around slowly can also ease the pain. The cramp typically releases after a minute or two, though your muscle might feel sore afterward, like you just finished a tough workout.