The American Heart Association recommends 30 minutes of aerobic physical activity a day at moderate intensity. Unfortunately, this guideline is misleading.

In 1995 the Centers for Disease Control and Prevention (CDC) and the American College of Sports Medicine (ACSM) made a public health recommendation that every U.S. adult should accumulate 30 minutes or more of moderate-intensity physical activity on most, preferably all, days of the week.

The recommendation seemed clear enough, but was misinterpreted by many. Some believed that higher-intensity activity would not be beneficial, while others considered it to mean that any movement would suffice. Therefore, in 2007 the following new guidelines were issued:

Healthy adults age 18 to 65 need moderate-intensity aerobic physical activity of at least 30 minutes per session on five or more days per week, or vigorous-intensity aerobic activity for at least 20 minutes three or more days per week.

Combinations of moderate- and vigorous-intensity activity can be performed to satisfy these requirements. In addition, every adult should perform activities that maintain or increase muscular strength and endurance a minimum of two days each week.

In order to understand these guidelines fully, it is important to understand what constitutes moderate and vigorous intensity.