Other forms: exertions
Exertion is effort. Exercise requires physical exertion. Listening to great jazz requires mental exertion. What kind of exertion does jazzercise require? Perhaps too much.
Ex– means out. Exertion means energy is coming out — so much so that when you’re done, you may feel exhausted. The opposite of ex- is in-, as in inertia — something you need exertion to overcome.