Physical Training incorporating popular drink (4)
I believe the answer is:
pint
'drink' is the definition.
(pint is a unit of liquid volume)
'physical training incorporating popular' is the wordplay.
'physical training' becomes 'pt' (Physical Training).
'incorporating' is an insertion indicator.
'popular' becomes 'in' ('in' can mean trendy).
'pt' placed around 'in' is 'PINT'.
(Other definitions for pint that I've seen before include "small amount" , "Measure of the plain man's alcoholic drink" , "Unit of beer" , "The working man's drink measure" , "Quantity" .)