Muscle Spasm

Ever had a painful, annoying twitch in your muscle and wondered what could be the cause.

Muscle Spasm: persistent involuntary hyper tonicity of one or more muscles usually of central origin and commonly associated with pain and excessive irritability.

A muscle spasm commonly lasts 4 to 5 days.

Muscles that are in spasm produce too much lactic acid: a waste product from the chemical reaction inside muscle cells. When muscles contract, the small blood vessels traveling through the muscles are pinched off (like a tube being pinched between your thumb and forefinger), which causes a build up of lactic acid. If the muscle cells cannot relax and too much lactic acid builds up, it is sometimes described as a painful burning or twitching sensation. Massage therapy encourages the muscle to relax which opens up the blood vessels, and the lactic acid is eventually washed away by fresh blood flowing into the muscle.

Definition - Merriam-Webster's Medical Dictionary, © 2002 Merriam-Webster, Inc.
http://dictionary.reference.com/browse/muscle spasm.