All Americans should be regularly physically active to improve overall health and fitness and to prevent many adverse health outcomes. The benefits of physical activity occur in generally healthy people, in people at risk of developing chronic diseases, and in people with current chronic conditions or disabilities. The Physical Activity Guidelines for Americans (2008) gives guidance on the amount of physical activity that will provide health benefits for all Americans. In addition to presenting the Guidelines, this Chapter gives an overview of research findings on physical activity and health.

Physical activity affects many health conditions, and the specific amounts and types of activity that benefit each condition vary. One consistent finding from research studies is that once the health benefits from physical activity begin to accrue, additional amounts of activity provide additional benefits.

Although some health benefits seem to begin with as little as 60 minutes (1 hour) a week, research shows that a total amount of 150 minutes (2 hours and 30 minutes) a week of moderate-intensity aerobic activity, such as brisk walking, consistently reduces the risk of many chronic diseases and other adverse health outcomes.

Examining the Relationship between Physical Activity and Health

In many studies covering a wide range of issues, researchers have focused on exercise, as well as on the more broadly defined concept of physical activity. Exercise is a form of physical activity that is planned, structured, repetitive, and performed with the goal of improving health or fitness. So, although all exercise is physical activity, not all physical activity is exercise.

Studies have examined the role of physical activity in many groups—men and women, children, teens, adults, older adults, people with disabilities, and women during pregnancy and the postpartum period. These studies have focused on the role that physical activity plays in many health outcomes, including:

• Premature (early) death;
• Diseases such as coronary heart disease, stroke, some cancers, type 2 diabetes, osteoporosis, and depression;
• Risk factors for disease, such as high blood pressure and high blood cholesterol;
• Physical fitness, such as aerobic capacity, and muscle strength and endurance
• Functional capacity (the ability to engage in activities needed for daily living);
• Mental health, such as depression and cognitive function; and
• Injuries or sudden heart attacks.

These studies have also prompted questions as to what type and how much physical activity is needed for various health benefits. To answer this question, investigators have studied three main kinds of physical activity: aerobic, muscle-strengthening, and bone-strengthening.