They get harder the more you work out (3)
I believe the answer is:
abs
(Other definitions for abs that I've seen before include "Exercise to improve these" , "Some musculature" , "Stomach muscles (abbr)" , "ratings?" , "stopping system" .)
I believe the answer is:
abs
(Other definitions for abs that I've seen before include "Exercise to improve these" , "Some musculature" , "Stomach muscles (abbr)" , "ratings?" , "stopping system" .)