For a different, and perhaps larger, group of college students and adults the problem of exercise resolves itself into the problem of not overdoing it. For such a rule of thumb is: exercise to the point of mild fatigue, but not beyond it.
The amount of fatigue produced is probably the best measure of the amount of exercise that ought to be taken. On this score a statement prepared by the American Association for Health, Physical Education, and Recreation offers sound guidance.
"The ability to recuperate after exercise is a good guide at any age. Recuperation should be reasonably prompt. If
(1) breathing and heart rate are still greatly accelerated at the end of ten minutes after exercise, and if
(2) there is marked weakness or fatigue persisting after a two-hour rest period,
(3) restlessness with broken sleep after retiring for the night, or
(4) a sense of definite fatigue the day following, the exercise has been too severe or too prolonged for that person in his present stage of physical training and strength."