Push up (5)
I believe the answer is:
boost
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">push up</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for boost that I've seen before include "Help to increase" , "Promote" , "Improve - pick-me-up" , "Encourage; push up" , "promotion" .)