On this, exercise is routine drudgery (9)
I believe the answer is:
treadmill
This clue is a double definition.
'on this exercise' is the first definition.
'routine drudgery' is the second definition.
(I've seen this before)
'is' is the link.
(Other definitions for treadmill that I've seen before include "It enables one to work out" , "Endlessly tedious job" , "hard labour" , "Wearisome routine" , "Boring routine; old rotary device" .)