Definitions for "Exertion"
The act of exerting, or putting into motion or action; the active exercise of any power or faculty; an effort, esp. a laborious or perceptible effort; as, an exertion of strength or power; an exertion of the limbs or of the mind; it is an exertion for him to move, to-day.
use of physical or mental energy; hard work; "he got an A for effort"; "they managed only with great exertion"
Exertion is a concept describing the use of physical or perceived energy. It normally connotates a strenuous or costly effort related to physical, philosophical actions and work.
In economic terms, exertion is synonymous with labor that is done to earn a living. Activities in which we exert ourselves for the fun of doing it are not "exertion" in the economic sense.