Physical or mental effort and energy put into doing something challenging.
From Latin 'exertio' (ex- 'out' + serere 'to join, bind'). Originally meant 'effort' in a physical sense, evolved to include mental and emotional effort.
Exertion is one of those words that reminds us why we need rest days—your body literally counts the effort you put in, and without recovery time, exertion becomes exhaustion.
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