Muscle PC tries to move (7)
I believe the answer is:
triceps
'muscle' is the definition.
(I know that triceps is a muscle)
'pc tries to move' is the wordplay.
'to move' is an anagram indicator.
'pc'+'tries'='pctries'
'pctries' with letters rearranged gives 'TRICEPS'.
(Other definitions for triceps that I've seen before include "one can't bend the elbow!" , "Muscles" , "One stretches out an arm!" , "Extensor muscle" , "Source of uplifting strength" .)