John is trying to gain more muscular strength to improve his performance in rock climbing. He currently runs 5 times a week at 65-85% of his max heart rate but has not seen any improvements. What fitness principle is he overlooking in his fitness plan?

(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!

Answer its calculated by subtracting your age from 220;