Think of exercise as a menu rather than a diet. Choose a number of different physical activities that are personally enjoyable such as sports, dancing, or biking. Develop an interest or hobby that requires physical activity. Adopt simple routines such as climbing the stairs instead of taking the elevator, walking instead of driving to the local newsstand, or canoeing instead of zooming along in a powerboat. Try cross training (alternating between several types of exercises). Exercise with friends. Consider getting a dog. One study found that dog owners walk almost twice as much as those who do not own a dog. Regular walking is a good way to improve health.

Don't eat for 2 hours before vigorous exercise. Drink plenty of fluids before, during, and after a workout. Adjust your activity level according to the weather, and reduce it when you are fatigued or ill. When exercising, listen to the body's warning symptoms, and consult a doctor if exercise causes chest pain, irregular heartbeat, unusual fatigue, nausea, unexpected breathlessness, or light-headedness.

•Practice warm-up exercises for 5 - 10 minutes at the beginning of an exercise session. Older people need a longer period to warm up their muscles. Strengthening exercises, quiet calisthenics, and walking are ideal.
•To cool down, you should walk slowly until the heart rate is 10 - 15 beats above your resting heart rate. Stopping too suddenly can sharply reduce blood pressure, and is dangerous for older people. It may also cause muscle cramping.
•Stretching may be appropriate for the cooling down period, but it must be done carefully for warming up because it can injure cold muscles. (There is no clear evidence, however, that stretching reduces muscle injuries.)

Warming up before exercise and cooling down after is just as important as the exercise itself. By properly warming up the muscles and joints with low-level aerobic movement for 5 - 10 minutes one may avoid injury. Cooling down after exercise by walking slowly, then stretching muscles, may also prevent strains and blood pressure fluctuation.

For most people, exercise may be divided into three general categories:
•Aerobic or endurance
•Strength or resistance
•Flexibility

A balanced program should include all three. Speed training is also a major category, but generally only competitive athletes practice it.

•Protection from heart attack, stroke, diabetes, dementia, depression, colon and breast cancers, and early death
•Builds endurance
•Keeps the heart pumping at a steady and high rate for a long time
•Boosts HDL ("good") cholesterol levels
•Helps control blood pressure
•Strengthens the bones in the spine
•Helps maintain normal weight
•Improves one's sense of well-being

Types of Aerobic Exercise. Aerobic exercise is usually categorized as high or low intensity. High intensity aerobic exercise is further classified as high or low impact. Examples of each include the following:

•Low- to moderate-impact exercises: Walking, swimming, stair climbing, step classes, rowing, and cross-country skiing. Nearly anyone in reasonable health can engage in some low- to moderate-impact exercise. Brisk walking burns as many calories as jogging for the same distance and poses less risk for injury to muscle and bone. •High-impact exercises: Running, dance exercise, tennis, racquetball, squash. Perform high-impact exercises no more often than every other day, and less often for those who are overweight, elderly, out of condition, or have an injury or other medical problem that would rule out high-impact.

Aerobic Regimens. As little as one hour a week of aerobic exercises is helpful, but 3 - 4 hours per week are best. Some research indicates that simply walking briskly for 3 or more hours a week reduces the risk for coronary heart disease by 45%. In general, the following guidelines are useful for most individuals:

•For most healthy young adults, the best approach is a mix of low- and higher-impact exercise. Two weekly workouts will maintain fitness, but three to five sessions a week are better.
•People who are out of shape or elderly should start aerobic training gradually. For example, they may start with 5 - 10 minutes of low-impact aerobic activity every other day and build toward a goal of 30 minutes per day, three to seven times a week. (For heart protection, weekly total is the key.)
•Swimming is an ideal exercise for many elderly people, and for certain people with physical limitations. People with physical limitations include pregnant women, individuals with muscle, joint, or bone problems, and those who suffer from exercise-induced asthma.
•People who seek to lose weight should concentrate on calories burnt each week, not the number of workout sessions.

One way of gauging the aerobic intensity of exercise is to aim for a "talking pace," which is enough to work up a sweat and still be able to converse with a friend without gasping for breath. As fitness increases, the "talking pace" will become faster and faster.

Shoes. All that's really necessary for a workout is a good pair of shoes that are made well and fit well. They should be broken in, but not worn down. They should support the ankle and provide cushioning for walking as well as for impact sports such as running or aerobic dancing. Airing out the shoes and feet after exercising reduces chances for skin conditions such as athlete's foot.

Clothing. Comfort and safety are the key words for workout clothing. For outdoor nighttime exercise, a reflective vest and light-colored clothing must be worn. Bikers, inline skaters, and equestrians should always wear safety devices such as helmets, wrist guards, and knee and elbow pads. Goggles are mandatory for indoor racquet sports. For vigorous athletic activities, such as football, ankle braces may be more effective than tape in preventing ankle injuries.

Aerobic-Exercise Equipment. Home aerobic exercise machines can be adapted to any fitness level and used day or night. Before investing in any exercise machine, however, it is wise to first test it at a gym. In addition, initial supervised training when using these machines can reduce the risk of injury that might occur with self-instruction.

Very inexpensive exercise machines tend to be flimsy and hard to adjust, but many sturdy machines are available at moderate prices. The higher-end models may utilize computers to record calories burned, speed, and mileage. Their readouts may provide motivation and gauge the intensity of a workout, however, they are not always accurate.

The following are a few observations on specific equipment:

•A good floor mat is important to provide cushioning for all home exercises.
•A simple jump rope improves aerobic endurance for people who are able to perform high-impact exercise. Jumping rope should be done on a floor mat plus a surface that has some give to avoid joint injury.
•For burning calories, the treadmill has been ranked best, followed by stair climbers, the rowing machine, cross-country ski machine, and stationary bicycle. (Elliptical trainers, however, may be even better than treadmills for increasing heart rate, calorie expenditure, and oxygen consumption.)
•Stationary bikes condition leg muscles and are fairly economical and easy to use safely. The pedals should turn smoothly, the seat height should adjust easily, and the bike's computer should be able to adjust intensity.
•Stair machines also condition leg muscles. They offer very intense, low-impact workouts and may be as effective as running with less chance of injury.