Painful muscle contraction (5)
I believe the answer is:
cramp
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">painful muscle contraction</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for cramp that I've seen before include "Muscular spasm, very painful" , "Involuntary and painful contraction of a muscle" , "Painful muscle problem" , "Confine - muscular spasm" , "restraint" .)