Concept of muscle’s pulling power (11)
I believe the answer is:
abstraction
'concept' is the definition.
(abstraction is a kind of concept)
'muscle's pulling power' is the wordplay.
'muscle's' becomes 'abs' (short for abdominal muscle).
'pulling power' becomes 'traction' (I've seen this before).
'abs'+'traction'='ABSTRACTION'
'of' acts as a link.
(Other definitions for abstraction that I've seen before include "theory" , "That's the general idea" , "Withdrawal from" , "Theoretical concept - removal" , "wool-gathering?" .)