Talk about exercise in run (7)
I believe the answer is:
operate
'run' is the definition.
(I know this)
'talk about exercise' is the wordplay.
'talk' becomes 'orate' (to orate is to give a speech).
'about' indicates putting letters inside.
'exercise' becomes 'pe' (Physical Education).
'orate' enclosing 'pe' is 'OPERATE'.
'in' acts as a link.
(Other definitions for operate that I've seen before include "Work as a surgeon" , "Carry on business" , "effect" , "Conduct business in a theatre" , "Perform as surgeon does" .)