Americans who are wondering just how much physical activity is enough may find an answer in the Physical Activity Pyramid. A simple guide to prescription for physical activity, the program includes some information that individuals may not be including in their exercise assessment.

Writing for ACSM's Health & Fitness Journal, Charles B. Corbin, Ph.D., FACSM and Robert P. Pangrazai, Ph.D., outline a structure that classifies physical activity into six different types, illustrates each activity and its benefits, and identifies the frequency, intensity, time and type (FITT formula) of each. Corbin and Pangrazai expanded on the FIT (Frequency, Intensity, Time) formula for physical activity developed about 20 years ago, adding choices of type.

"The formula for exercise begins with the individual," said Corbin. "But we have found that 20 minutes, three times a week, at your target heart rate doesn't describe everything an individual can do to increase overall health and fitness. Sometimes it's possible to include everyday activity in that regimen and still come out ahead."

Everyday activities, including walking instead of driving to work, using stairs instead of the elevator, and house/yard work, occupy the first level, referred to as Lifestyle Physical Activity, of the Physical Activity Pyramid. Or, for younger children, free play activities are considered Lifestyle Physical Activity. Level 1 effort equal to 30 minutes of brisk walking, done most days of the week, meets the recommendations set forth by the Surgeon General of the United States.

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Level 2, Active Aerobics or Active Sports and Recreation, is more vigorous than Lifestyle Physical Activity, and sometimes requires extra equipment and time. Because these activities involve elevation of the heart rate, they can be performed less often�perhaps three days a week for 20 minutes at a time�with the same health benefits as Level 1. Examples of Level 2 activity are aerobic dance, step aerobics, basketball, tennis, bicycling and volleyball. Some sports, such as golf, can be considered lifestyle activities, because the exercise is similar to walking to work.

At Level 3 of the Physical Activity Pyramid, we find Flexibility and Muscle Fitness Exercises. Developed to improve specific joint range-of-motion and muscle endurance characteristics, these exercises include stretching, flexing and training sets and repetitions. They don't always require specialized equipment, but it is necessary to learn proper technique. ACSM recommends that the individual seeking fitness use the flexibility exercises for each major muscle group three to seven days a week, and stretch to the point of mild discomfort, not pain. For muscular endurance, doing the muscle fitness exercises, again for each major muscle group, two or three days a week with a day of rest between, will maintain muscular tone and strength.