Exercise is exertion.
- Doing an extremely hard crossword puzzle that taxes your brain is an example of mental exertion.
- When you exercise your authority and forbid someone from going to a party, this is an example of an exertion of your authority.
Exertion is defined as physical or mental effort, or to the use of force or influence.
- the act, fact, or process of exerting; active use of strength, power, etc.; exercise
- energetic activity; effort
The act or an instance of exerting, especially a strenuous effort.
- Adjectives often used with "exertion": physical, mental, etc.