In 1996, the Surgeon General recommended exercising enough to burn at least 150 calories—the equivalent of walking about one and a half miles per day. But in the beginning, this might be unrealistic. Start with an amount you’re comfortable with—even ten minutes of walking a day—and work your way up as that becomes easier and easier.

As physical activity becomes a more regular and enjoyable part of your routine, try gradually working up to thirty to forty-five minutes of brisk walking or its equivalent per day. Aerobic exercise should be stimulating but not stressful; it should take effort but not be exhausting.

Once you’re reasonably fit, you should be able to sustain it for twenty to thirty minutes or longer. Another good way to measure your intensity is that if you can’t talk while you do it, you’re probably going too hard; if you can sing while you do it, you’re probably not going hard enough.

Remember to do a five- to ten-minute warm-up and cooldown before and after each session of aerobic activity to avoid injury. Doing the same activity you have planned at a lower intensity (walking slowly before a power walk, for example) is a great way to accomplish this.

You may be wondering how you’re going to fit these new activities into your already busy life. I can’t tell you how to get more hours in a day, but I can tell you that exercise is too important not to find time for it. If you want to exercise for half an hour a day, think about substituting it for something you now do for thirty minutes.

Do you really need to watch two hours of television in the evening? Could the thirty minutes you spend sending e-mails to friends during lunch be shortened? Could you convince your neighbor to join you so you can socialize and exercise at the same time? Be realistic.

Don’t schedule exercise for after dinner if you know that’s when you always have to help the kids with their homework. In addition to the time you schedule every day, look for ways to add bits of activity and recreational exercise—an extra lap around the mall when you’re shopping or a Saturday morning bike ride, for example.

Studies show that you can get some cardiovascular benefits even if you break up your thirty minutes of daily exercise into three or four eight- to ten-minute sessions, as long as they are of moderate intensity. However, it’s unsafe to do frequent bouts of high-intensity activity.

After the first week, adjust your schedule in places where it may not be working. The good news is that as your conditioning increases, you’ll be able to boost the intensity of your exercise without further exerting yourself. This means that you’ll be able to fit more into your allotted time.

For example, you’ll be able to walk four miles in the time it used to take you to do three. It should come as no surprise that the most successful exercise program is one well suited to the individual. To give yourself the best odds of sticking with a program, stack the deck in your favor by considering the following points before you start.

• What do you like to do? If you hate jogging, you won’t be able to maintain a program based on jogging no matter how good it is for you. Don’t expect to change your likes and dislikes, especially when starting out.

• What kind of setting works for you? Do you have easy access to a pool? If not, swimming probably isn’t a good choice. Likewise, if you live in a particularly hot or cold climate, certain outdoor activities may not be sustainable. On the other hand, if there’s a network of biking and jogging trails near your office, a routine of lunchtime exercise might be just the ticket.

• Do you like exercising alone or with others? Many people find the solitude of swimming or running ideal for contemplation. Others enjoy the motivation and support of a group aerobics class or the company of a walking companion.

• How much money do you want to spend? You’ll need to weigh expense against other factors, such as the ability to exercise indoors or to participate in a particular activity. Many exercise options are available at a range of prices. You can get great workouts for virtually no money by walking, running, or hiking.

A set of inexpensive home barbells can produce the same results as a health club membership. However, some people may find that the money they spend for gym privileges is a motivating factor. Only you know what will work best in your particular case. But it may take some trial and error to figure it out.

• What’s your current level of fitness? If you’ve been sedentary for a while, it’s unrealistic (not to mention dangerous) to attempt a five-mile run your first day out. One of the quickest ways to sabotage an exercise program is with an injury.

A more practical approach would be to start with walking and work up to greater levels of intensity as your level of fitness increases. If you’ve had previous injuries or suffer from a chronic disease, talk to your doctor about your physical limitations before deciding on a type of exercise.

• How can you stay motivated? To be successful, exercise has to be thoroughly integrated into your lifestyle; it should be something you do as routinely as eating, sleeping, and taking your morning shower. Unfortunately, that can be difficult, as you may already know. The information that follows may help you stay on course when your motivation starts to flag. Remember, the result is worth the effort.