A: A Twitch
A single contraction that lasts only a fraction of a second is called a muscle twitch. Its when the muscle seizes up for a quick pulse then relaxes.
constant contraction of a muscle is called the muscle tone
It is called concentric isotonic contraction.
An involuntary muscle contraction is called a spasm.
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Tonus is the continous baseline muscle tone in the body.
Spasm
An eccentric contraction is one that causes a muscle to lengthen.
Creatinine
Often it is called a cramp.
If the muscle can not shorten because the muscle is trying to move a load that is greater than the force, then the contraction is isometric.
It is called a Tracheospasm