Section 1. Fundamentals

Chapter 6. Exercise and Fitness

Topics: Introduction | Benefits of Exercise | Starting an Exercise Program | Preventing Injury | Choosing the Right Exercise

Starting an Exercise Program

Many people can begin an exercise program without consulting their doctor. However, people who have heart and lung disease, diabetes, or any other serious medical condition should talk with their doctor first, as should older people. People taking medication, especially for chronic illness, should consult with their doctor as well. Certain drugs may limit the ability to exercise, such as beta-blockers, which slow the heart rate (see Section 3, Chapter 22), and sedatives, which can cause drowsiness and increase the risk of falling.

People who have done no exercise previously and who are seriously out of shape may benefit from consulting their doctor before starting an exercise program. In some cases, exercise must be supervised by a physical therapist or other health care professional or by an experienced, licensed trainer.

The safest way to start an exercise program is to perform the chosen exercise or sport at a low intensity until the legs or arms ache or feel heavy. If muscles ache after just a few minutes, the first workout should last only that long. As fitness increases, a person should be able to exercise longer without feeling muscle pain. However, some discomfort is necessary for developing stronger, larger muscles. Over time, a person can increase the intensity and duration of exercise.

Type of Exercise

A major distinction among different types of exercise is whether they are aerobic ("with oxygen") or anaerobic ("without oxygen"). Most forms of exercise have components of both.

Aerobic Exercise: This term refers to exercise that requires oxygen from the air to get to the muscles, thus the heart and lungs are forced to work harder than normal. Running, biking, swimming, and skating are examples of aerobic exercise. Aerobic exercise tends to burn a great deal of calories and improves cardiac function more than does anaerobic exercise. However, it is less effective at building strength and muscle mass.

Anaerobic Exercise: This term refers to exercise that requires intense straining for short periods of time. Weight lifting and isometrics (in which one part of the body is used to resist the movement of another part) are examples of anaerobic exercise. Anaerobic exercise relies on energy sources that are stored in the muscle and, unlike aerobic exercise, is not dependent on oxygen from the air. Overall, anaerobic exercise burns fewer calories than does aerobic exercise and may be somewhat less beneficial for cardiovascular fitness. However, it is better at building strength and muscle mass and still benefits the heart and lungs. In the long run, increased muscle mass helps a person become leaner and lose weight, because muscle uses large amounts of calories.

Intensity, Duration, and Frequency

Exercise is always a balance between intensity (how hard the exercise is), duration (how long a person exercises), and frequency (how often a person exercises). For most people, intensity should continue to increase as they get stronger, whereas duration and frequency remain constant once a certain level is reached.

To strengthen the heart, exercise must be performed at a reasonably high intensity. Intensity can be assessed in several ways. In one method, intensity is considered adequate (that is, enough to be beneficial) if the heart rate (measured in beats per minute) increases at least 20 beats above the resting heart rate. In another, more complex, method, intensity is considered adequate if the heart rate is between 70% and 85% of a person's estimated maximum heart rate, which is 220 minus the person's age. However, this calculation is somewhat conservative, especially for people who are physically fit. A less quantitative approach is to consider intensity to be adequate if exercise is accompanied by reasonably heavy breathing and sweating, assuming that the environmental temperature is not inordinately hot. Very heavy breathing and profuse sweating indicate a high level of intensity. Another method by which intensity is considered adequate is to work to failure. This approach is often used by weight lifters, who continue lifting until they cannot possibly do one more repetition.

At first, most people can exercise for only a few minutes before they fatigue. For most people, exercise eventually should be performed at the most tolerable intensity for about 30 to 60 minutes at a time. This duration provides optimal benefits both for training muscles and for cardiovascular conditioning. Extending the duration much beyond this amount of time does not substantially improve muscle strength or endurance.

Most people do not benefit from exercising more than 3 to 4 times a week. Although the heart can be exercised several times a day every day, skeletal muscles start to break down when exercised intensely more often than every other day. The day after an adequate workout, bleeding and microscopic tearing can be seen in muscle fibers, which is why muscles feel sore. Exercisers should allow about 48 hours for muscles to recover after exercise. After very vigorous exercise, a muscle group may take several days to heal completely. Allowing the muscles to heal makes them stronger.

Different exercises stress different muscle groups. In aerobic exercise, for example, running stresses primarily the lower leg muscles; landing on the heels and rising on the toes exerts the greatest force on the ankle. Riding a bicycle stresses primarily the upper leg muscles; pedaling works the front thigh muscles (quadriceps) and hips. Rowing and swimming stress the upper body and back. These exercises can be alternated daily to avoid injury. In anaerobic exercise, such as weight lifting, it is usually best to alternate the muscle groups being trained. An ideal schedule, for example, alternates exercise for the upper body on one day with exercise for the lower body on the next.

Additionally, people should vary the way they train their muscles over time. The body adapts to routine, so that performing the same exercises over time becomes less effective in building strength and cardiovascular fitness. Therefore, weight lifters should alter their routines every few weeks, and aerobic exercisers should alternate among the different forms of aerobic exercise available.