Answer:
between 55% and 80%
Step-by-step explanation:
A heart rate between 50% to 70% corresponds to moderate excercise according to the American Heart Association, while a heart rate between 70% and 85% corresponds to streneous excercise.
Therefore, the American College of Sports recommends a healthy balance (going by total heart rate) between moderate excercise and strenous excercise every week.