Men back in shape, wearing trousers (5)
I believe the answer is:
dudes
'men' is the definition.
(dude is a kind of man)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for dudes that I've seen before include "American blokes" , "Civilians, to a cowboy" , "American dandies or city dwellers" .)