Free muscle work out (7)
I believe the answer is:
absolve
'free' is the definition.
(to absolve is to free or spare from blame)
'muscle work out' is the wordplay.
'muscle' becomes 'ab' (short for abdominal muscle).
'work out' becomes 'solve' (I've seen this before).
'ab'+'solve'='ABSOLVE'
(Other definitions for absolve that I've seen before include "Forgive sins" , "Cleanse" , "Declare (someone) guilt-free" , "Clear of blame or guilt" , "Free (a person) from guilt" .)