Sharp jerks after exercise, possibly (7)
I believe the answer is:
perhaps
'possibly' is the definition.
(synonyms)
'sharp jerks after exercise' is the wordplay.
'jerks' is an anagram indicator (I've seen 'jerk' mean this).
'after' says to put letters next to each other.
'exercise' becomes 'pe' (Physical Education).
'sharp' anagrammed gives 'rhaps'.
'rhaps' after 'pe' is 'PERHAPS'.
(Other definitions for perhaps that I've seen before include "Could be, maybe" , "Conceivably" , "Quite possibly" , "Not necessarily" , "say" .)