How much exercise should I do?

Experts recommend 30-60 minutes of exercise per day. The 60-minute suggestion is based on the National Academy of Science's ideal recommendation for people who are trying to lose weight. But you'll get real health benefits (and burn lots of calories) even if you don't work out that much -- especially if you haven't been exercising at all up to now.

While 30 minutes of physical activity is considered enough to lower your risk of heart disease, stroke, and high blood pressure, even 10 minutes a day will do you good. Remember that you don't have to do all your exercise in one session: A 30-minute aerobics workout in the morning, a 20-minute walk after work, and 10 minutes of mopping the floor after dinner can do the trick.

What types of exercise are better for weight loss?

• Choose endurance activities for weight loss such as jogging, aerobics, bicycling, rowing, or swimming.
• Exercise at a moderately intense level. You should be able to talk without running out of breath during the activity.
• Exercise for more than 40 minutes.
• During the first 20 minutes, your body taps into your sugar reserves (carbohydrates stored as blood glucose and muscle glycogen). Between 20 to 40 minutes of exercise, the body continues to use up your sugar reserves and starts to tap into your body fat.
• After 40 minutes the body starts to burn even more fat.
• Choose aquatic workouts or exercise in the cold. This causes the body to burn more energy and melt fat more quickly. The body draws on its fat reserves to stay warm.

What if I don’t have time to exercise 60 minutes a day?

The 60-minute suggestion is based on the National Academy of Science's recommendation for people who are trying to prevent weight gain, or keep themselves from regaining after weight loss -- not for people who are trying to increase or maintain their cardio-respiratory fitness or health. There's plenty of research to show that 30 minutes of physical activity a day will help you gain lots of health and fitness benefits.

Remember that you don't have to do all your exercise in one session. If you already exercise vigorously at the gym several times a week, there's no reason to quit. But if 60 minutes seems like too much for you, try 30 minutes a day as a starting goal.

Where do I start if I have never exercised?'

If you're new to exercise, or have struggled with it in the past, talk with your doctor about your exercise plans. After that, start by incorporating more activity into your daily life. For instance:

• If you always take the elevator, try the stairs.
• If you try to park next to the door of wherever you're going, park further away and walk.
• If your habit is to eat at your desk, take a 10- to 20-minute walk first, then have your lunch (or take a walk after you eat).

Instead of watching TV all day Saturday and Sunday, plan active weekends. Go to the park, take a walking tour, ride your bike, or row a boat.
If you prefer a more ambitious routine, you can join a gym or try working out at home. Try for 30 to 60 minutes of continuous aerobic activity (such as swimming, biking, walking, dancing, or jogging) at least three to five times a week, at 60% to 90% of your maximum heart rate. Weight training can also help tone your muscles and elevate your resting metabolism rate (the rate that the body burns fuel for energy). Try at least one set (eight to 12 repetitions) each of eight to 10 different exercises, targeting each of the body's major muscle groups.

Whatever plan you decide on, it's a good idea to set weekly goals:

• Write down what activity you plan to do, on what day of the week, for how long, and at what time of day. Be as specific and realistic as possible. For instance, write down "Tuesday: Walk for 20 minutes at 7 p.m., to the park and back."
• At the end of each week, review your goals and set new ones for the upcoming week.

Research shows that setting goals will help you stick to your program. It will clarify what you're supposed to do and let you track your progress. If you hit a roadblock later on, you can refer to what has worked in the past, or use your accomplishments to re-energize yourself.

What if I am physically unable to exercise due to a medical condition?

There is virtually no medical condition that will keep you from doing any type of exercise. Even people with heart failure -- who were long told not to exercise at all -- can benefit from moderate amounts of activity.

And people with limited mobility can often do water exercises, or do yoga or other exercises while seated in a chair (some "chair exercise" videos are now on the market). Of course, if you have any medical condition, check with your doctor before starting any exercise program.

Should I lift weights?

Check with your doctor. Lifting weights will not only help you lose weight, but maintain the loss. Here's why:

• Muscle keeps your metabolism revved up, burning calories, fat, and glucose (sugar).
• When you lose weight, up to 25% of the loss may come from muscle, resulting in a slower metabolism. Weightlifting will help preserve or rebuild any muscle you lose by dieting.
• Muscle helps you with aerobic exercise. The stronger you are, the better you will be at any aerobic activity.
• Weight training improves your body's muscle-to-fat ratio (you end up with less body fat and more muscle), which improves both your health and your fitness level.
• Gaining muscle will help you look better as you define and tone your physique.

What is interval training?

In interval training, you alternate between bursts of higher-intensity exercise and periods of less-intense exercise (or "active rest"). As you get more fit, you decrease the "rest" time and increase the high-intensity periods. You'll see big fitness gains if you train this way regularly.

For example, if you now run for 30 minutes at 6 mph, try this routine: Jog for five minutes to warm up. Then, increase your speed to 6.5 mph for one to two minutes (less if you can't go that long). Then, jog for a few minutes at your normal speed, then again at the faster speed, and so on until you reach your time limit. Your ratio of work to active rest would be 2:3 if you ran for two minutes at 6.5 mph, then jogged for three minutes at 6 mph.

You can also use your heart rate to set intervals. For example, if your heart rate hits 70% of your maximum when you jog at 6 mph, start at that speed. Then increase either your speed or elevation (if you're on a treadmill) to get your heart rate to 85% or 90% of your maximum heart rate for one to three minutes. Then, go back to jogging at the 70% heart rate, and continue alternating.

We recommend interval training just once a week to start, as it is more intense than you may be used to. Once you get a feel for it, you can do it more often.

What is BMI and why is it useful?

The body mass index (BMI) is a simple way for men and women to estimate body fat based on their height and weight. From the BMI, it is possible to determine your healthy weight range.

For the majority of Americans, the BMI is the most up-to-date and scientifically sound method available for determining healthy weight. One of the limitations of BMI is that it can over-predict overweight or obesity in people who are lean and muscular.

It is important to know that people who are classified as overweight or obese can still be healthy as long as they are fit. In one well-known study, fit people with BMIs that classified them as overweight or obese were healthier and lived longer than unfit people who were at normal weight.

Does exercise help you lose weight?

Exercise alone does not necessarily make you lose weight, but it will help you to slim down and reshape your body by decreasing fat and increasing muscle. Regular exercise:

• Helps you burn calories that you have consumed during meals
• Helps combat muscle loss that can occur when you lose weight
• Builds up your muscle tissue
• Increases the amount of calories that you burn. The more muscular you are, the more calories you burn.