Why do muscles become fatigued?

It depends on the amount of glucolysis, water, and other molcules included in your body to be able to convert into acid. the acid is what cause the fatigue in the muscles

(a) is not correct because one does not get increased cholesterol  from lifting weights.(b) is not correct because lifting weights cannot reduce the risk of a hereditary disease.(c) is not correct because back pain isn't a benefit! and plus, if he lifts weights properly, he should not have back pain.(d) is the correct answer because his ligaments will gain mass, making it easier for him to carry heavier weights and he will also be stronger!