All healthy adults age 18 to 65 years need moderate-intensity aerobic physical activity for at least 30 minutes five days per week or vigorous-intensity aerobic physical activity for at least 20 minutes three days per week, according to updated guidelines released by the American Heart Association and published online August 1 by Circulation.

In addition to the recommendations for aerobic exercise, the guidelines note that adults benefit from performing activities that maintain or increase muscular strength and endurance for at least two days per week. It is recommended that 8-10 exercises using the major muscle groups be performed on two non-consecutive days. To maximize strength development, a resistance (weight) should be used for 8-12 repetitions of each exercise to the point of willful fatigue.

The preventive recommendation specifies how adults, by engaging in regular physical activity, can promote and maintain health and reduce risk of chronic disease and premature death.

A companion recommendation similar to the updated recommendation for adults is specifically applied to adults age 65 years and older and adults age 50 to 64 years with chronic conditions or physical functional limitations (namely, arthritis) that affect movement ability or physical fitness.

The recommendations are an update and clarification of the 1995 recommendation from the Centers for Disease Control and Prevention (CDC) and American College of Sports Medicine on the types and amounts of physical activity needed by healthy adults to improve and maintain health. The intent is to provide a more comprehensive and explicit public health recommendation for adults based upon available evidence of the health benefits of physical activity.

The core recommendation remains fundamentally unchanged despite more than 10 years passing since it was issued. New science has been evaluated to understand the biological mechanisms by which physical activity provides health benefits and the physical activity profile (type, intensity, amount) that is associated with enhanced health and quality of life. This publication reflects a review of that evidence, and considers key issues not fully clarified in the original recommendation.

The new recommendation emphasizes the important fact that physical activity above the recommended minimum amount provides even greater health benefits. The point of maximum benefit for most health benefits has not been established but likely varies with genetic endowment, age, sex, health status, body composition and other factors. Exceeding the minimum recommendation further reduces the risk of inactivity-related chronic disease. Although the dose-response relation was acknowledged in the 1995 recommendation, this fact is now explicit.

The original recommendation introduced the concept of accumulating short bouts of physical activity toward the 30-minute goal, but there was confusion about how short these episodes could be. For consistency, the minimum length of these short bouts is clarified as being 10 minutes.

Muscle-strengthening activities have now been incorporated into the physical activity recommendation. The 1995 recommendation mentioned the importance of muscular strength and endurance but stopped short of making specific declarations in this area. Available evidence now allows the integration of muscle strengthening activities into the core recommendation.