To receive the benefits of physical activity, it's important not to tire too quickly. Pacing yourself is especially important if you've been inactive.

Target heart rates let you measure your initial fitness level and monitor your progress in a fitness program. This approach requires measuring your pulse periodically as you exercise and staying within 50 to 75 percent of your maximum heart rate. This range is called your target heart rate. Your maximum heart rate is about 220 minus your age.

When starting an exercise program, aim at the lowest part of your target zone (50 percent) during the first few weeks. Gradually build up to the higher part of your target zone (75 percent). After six months or more of regular exercise, you may be able to exercise comfortably at up to 85 percent of your maximum heart rate. However, you don’t have to exercise that hard to stay in shape.

Note: A few high blood pressure medications lower the maximum heart rate and thus the target zone rate. If you're taking such medicine, call your physician to find out if you need to use a lower target heart rate.

Information obtained from the American Heart Association.