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Muscle contraction is the tightening, shortening, or lengthening of muscles when you do some activity. It can happen when you hold or pick up something, or when you stretch or exercise with weights.

A muscle spasm — also known as a charley horse, muscle cramp or twitch — is a sudden, involuntary movement in one or more muscles. Common causes include stress, exercise, or dehydration, but nerve ...

Just when I thought I had a real handle on panic attacks (after all, I wrote a book on the topic), something new came to my attention. A number of people have recently mentioned that, during a panic ...