Belly muscles (3)
I believe the answer is:
abs
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">belly muscles</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for abs that I've seen before include "stopping system" , "ratings?" , "Stomach muscles (abbr)" , "Exercise to improve these" , "Some musculature" .)