Stress from 'sexercise' (6)
I believe the answer is:
strain
'stress' is the definition.
(I know that stress can be written as strain)
'from sexercise' is the wordplay.
I cannot quite understand how this works, but
'from' could be 'in' (I've seen this in other clues) and 'in' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for strain that I've seen before include "Family - tension" , "Pass through a filter" , "line of ancestry" , "Tension - tune" , "Muscle injury - tension" .)