Recess after physical session exercising, just tops (4)
I believe the answer is:
apse
'recess' is the definition.
(apse is a kind of recess)
'after physical session exercising just tops' is the wordplay.
'just tops' suggests taking the first letters (only the letters at the top).
The first letters of 'after physical session exercising' is 'APSE'.
(Other definitions for apse that I've seen before include "Church recess with domed or arched roof" , "room for an altar" , "inside church?" , "Peas (anag) - found in church" , "Niche in church" .)