You'll find gymnastics initially tiring, dear (3)
I believe the answer is:
pet
'dear' is the definition.
(I've seen this in other clues)
'you'll find gymnastics initially tiring' is the wordplay.
I cannot really understand how this works, but
'gymnastics' could be 'pe' (Physical Education) and 'pe' is found within the answer.
A single letter 't' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for pet that I've seen before include "Cherished animal" , "Favourite, darling" , "Tamed animal; sulk" , "Cat or dog" , "The darling one in a small temper" .)