Athletic facilities (4)
I believe the answer is:
gyms
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">athletic facilities</span>' is the definition.<br/ ><span class="explanation-format__explanation">(gym is a kind of athletic facility)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for gyms that I've seen before include "sporting facilities?" , "In brief, places of exercise" , "'Physical training facilities, in short (4)'" .)