These exertions could be either physical or spiritual.
Some people work at computers all day long and some have to stand all day by machines.
Those who drive each day sit on seats for hours with their hands on steering wheels. Business persons, who travel often, do not have a regular time to take their meals. All of these people suffer from certain tensions which cause fatigue. Fatigue can only be prevented or cured through exercising. Therefore, exercises are very important for a happy life and for maintaining efficiency in working.