Works and lectures about exercise (8)
I believe the answer is:
operates
'works' is the definition.
(I know this)
'lectures about exercise' is the wordplay.
'lectures' becomes 'orates' (to orate is to give a speech).
'about' means one lot of letters goes inside another.
'exercise' becomes 'pe' (Physical Education).
'orates' enclosing 'pe' is 'OPERATES'.
'and' acts as a link.
(Other definitions for operates that I've seen before include "Performs sugery" , "Acts" , "Functions" , "Directs or controls, machinery say" , "Performs, surgery perhaps" .)