Muscles stopping system (3)
I believe the answer is:
abs
I believe this is a double definition.
'muscles' is the first definition.
(I've seen this before)
'stopping system' is the second definition.
(short for anti-lock braking system in a vehicle)
(Other definitions for abs that I've seen before include "Exercise to improve these" , "Stomach muscles (abbr)" , "Some musculature" , "ratings?" , "stopping system" .)