An important research study that was conducted over a 40-year period on Harvard alumni found that expending 2,100 to 3,500 calories a week through physical activity produced the greatest health benefits (Paffenbarger, Hyde, & Wing, 1987). The type of activity was not as important as the amount of activity. Tennis players were no different from runners, provided they reached this weekly energy expenditure.

Depending on the capability of the individual, the goal of an exercise program should be to expend 300 calories a day. For higher fit individuals, 400 to 500 calories should be targeted. For less fit or poorly motivated individuals, 150 to 200 calories is probably more realistic. It is important to remember that you don't have to expend all the calories in one exercise session. In some instances it may be more desirable to reach this goal in two to three exercise sessions per day. For example, using a half hour during lunchtime at a sheltered workshop and adding a half hour in the evening before dinner will probably be enough to reach a goal of 200 to 300 calories. Walking before each meal for 20 minutes should achieve the same results.

There are many charts and textbooks that provide information on how many calories are "burned" performing a specific exercise. For example, a general guideline is that approximately 100 calories are "burned" walking one mile. Heavier individuals will expend more calories and lighter individuals will expend fewer calories because extra weight requires greater energy expenditure. Most fitness machines provide digital readouts of how many calories are being expended while using the equipment.