What is a muscle twitch?

Fibers contracting: The brain sends messages to the muckes (via nerves) to tell the muscle to move. Occasionally, the chemicals that mediate this process allow for a muscle (or part of a muscle) to contract without any planned action. Causes range from nothing at all ( most prople get them occasionally) to fatigue to vitamin/ mineral imbalance. If happening frequently, see your doctor to rule out systemic reason.

Depends on the type: If your leg or arm jumps you could have restless leg syndrome which is treatable.Other remedies may include more rest or evaluation of your body chemicals such as potassium.