Aerobic exercise does good things for your cardiovascular system and is an important part of weight management. Muscular conditioning can improve strength and posture, reduce the risk of lower back injury, and is also an important component of a weight management program. Flexibility exercise is needed to maintain joint range of motion and reduce the risk of injury and muscle soreness.

2. Aerobic exercise can be as simple as walking

Walking is a weight-bearing aerobic exercise. So are jogging, rope skipping and dance-exercise. Aerobic exercise is any activity that uses large muscle groups in a continuous, rhythmic fashion for sustained periods of time.

There are also non-weight-bearing aerobic exercises, such as bicycling, stationary cycling, swimming and rowing.

Keep the pace comfortable. A very important aspect of your exercise program is the intensity. You should exercise at a comfortable pace. You can measure your exercise heart rate to check the intensity of your exercising, or you can take the ''talk test.''

To measure your heart rate, take your pulse as soon as you stop exercising. Count your heartbeat for 10 seconds, then multiply that by six to convert it to a one-minute heart rate. If you keep your exercise heart rate within a range of 55 percent to 80 percent of an estimated maximum heart rate (220 minus your age), you're doing well.

The talk test is easier to accomplish. Just exercise at a pace that allows you to carry on a conversation while you're exercising.

How often should you exercise? Three to four days of aerobic activity is fine for general health maintenance. If you're trying to lose weight, aim for four or more days a week, being sure you take off at least one day a week.

How long should you exercise? Work up to 20 or more minutes per session for general health maintenance. For weight loss, gradually work up to 45 minutes or longer at low to moderate intensities in a low- or no-impact activity.

3. Strength conditioning gives you a choice

Pick calisthenics, free weights or machines. Just be sure that your strength training includes exercises for every major muscle group, including the muscles of the arms, chest, back, stomach, hips and legs.

Start with a weight that's comfortable to handle and keep it up for eight repetitions. Gradually add more repetitions until you can complete 12 repetitions. For greater strength conditioning, add more weight and/or more repetitions, in sets of eight to 12, when the exercise becomes easy.

Stretch for flexibility

Proper stretching involves holding a mild stretch of 10 to 30 seconds while you breathe normally. Always warm up before you stretch. Like strength conditioning, flexibility exercises should include stretching for all the major muscle groups.

One last thing to remember . . .

Always check with your doctor before beginning any exercise program, especially if you're over 40, or have cardiovascular risk factors, such as smoking, high blood pressure, high cholesterol, diabetes or a family history of heart disease.