Inspiring female, unnamed, having no sex before gym (7)
I believe the answer is:
euterpe
'inspiring female' is the definition.
(Greek muse of music)
'unnamed having no sex before gym' is the wordplay.
I cannot really see how this works, but
'gym' could be 'pe' (short for Physical Education) and 'pe' is located in the answer.
This may be the basis of clue (or it may be nonsense).
(Other definitions for euterpe that I've seen before include "inspiring female" , "Musical Muse" , "Muse of lyric poetry and music" , "Inspiration for writer" , "One of the Muses" .)