Complain intensely about tear in sides of gym shoe (5)
I believe the answer is:
gripe
'complain intensely' is the definition.
'gripe' can be an answer for 'complain' (griping is a kind of complaining). I'm unsure of the 'intensely' bit.
'tear in sides of gym shoe' is the wordplay.
'tear' becomes 'rip' (rip is a kind of tear).
'in' is an insertion indicator.
'sides of gym shoe' becomes 'ge' (I can't explain this - if you can you should believe this answer much more).
'rip' placed within 'ge' is 'GRIPE'.
'about' is the link.
Can you help me to learn more?
(Other definitions for gripe that I've seen before include "Grumble informally" , "beef" , "carp" , "Trivial complaint" , "Complain; colic (water)" .)