What would happen if humans didnt have muscle endurance?

Having low stamina often causes a person to feel tired after little exertion, and they may experience an overall lack of energy or focus. By increasing their stamina, a person can feel more energetic and complete daily tasks more easily.

Without muscle, muscles have a important role of to move the bones and enable the heart to beat

The person who utilize the progression principle will keep adding the difficulty of the exercise that he's doing, while the person who does not, will only stay stagnant.  the person that utilize progression principle, will get a stronger endurance because now his body is conditioned to do harsher routines.{the answer was already on verified)

Broken bone result of heredity