In good condition back providing time (3)
I believe the answer is:
fit
'in good condition' is the definition.
'back providing time' is the wordplay.
'back' is a reversal indicator.
'providing' becomes 'if' (I've seen this in other clues).
'time' becomes 't' (abbreviation).
'if' back-to-front is 'fi'.
'fi'+'t'='FIT'
(Other definitions for fit that I've seen before include "Adequate" , "Healthy, exercised" , "Sound in body or suitable" , "In trim" , "Strong" .)