Explain why exercise programs must increase in difficulty and duration over time to remain effective.

Exercise programs must increase in difficulty and duration to remain effective because of the principle of overload. As an individual exercises at a higher level, the body adapts to the increased demand and this higher level eventually becomes your body's new normal.

Explanation:

      x/140 = 25/100

we need to find the x to find the x multiply 140 and 25

and what do you get 3500.   and what is 3500 divided by 100

= 35

hpv is the answer