http://www.medscape.com/viewarticle/561348?src=mp
Primary Recommendation:
To promote and maintain health, all healthy adults aged 18 to 65 yr need
moderate-intensity aerobic (endurance) physical activity for a minimum of 30
min on five days each week or vigorous-intensity aerobic physical activity
for a minimum of 20 min on three days each week. [I (A)] Combinations of
moderate- and vigorous-intensity activity can be performed to meet this
recommendation. [IIa (B)] For example, a person can meet
