Muscle movement (5)
I believe the answer is:
spasm
'muscle movement' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for spasm that I've seen before include "Sudden muscular contraction" , "Involuntary contraction of muscles" , "Tic, sudden contraction" , "Painful muscle contraction" , "Muscle twitch" .)