Physical exercise (3-2)
I believe the answer is:
sit-up
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">physical exercise</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that sit-up is a type of stomach exercise)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for sit-up that I've seen before include "Exercise designed to strengthen stomach muscles" , "Physical exercise" , "Exercise done on the floor" .)