- Why Use the Body Mass Index (BMI)?
- Aerobic Exercise and Muscle Gains from Weightlifting?
- Should I Hold Off on Weight Training Until I Lose Weight?
- How Much Exercise Should I Do?
- I Don't Have Time to Exercise. I Hate Exercise.
- Where Do I Start if I Have Never Exercised?
- What Should My Heart Rate be During Exercise?
- My Weight Has Hit a Plateau. What Do I Do?
- What's the Bottom Line to Weight Loss?
- What if I Have a Medical Condition?
- What is Interval Training?
- Fat-Burning Mode vs. Cardio Mode at the Gym?
- What is Basal Metabolic Rate?
Get answers to your questions about exercise, and tips for getting the most from your workouts.
By Richard Weil, MEd, CDE
WebMD Weight Loss Clinic Exercise Physiologist
Reviewed by Louise Chang, MD
Are you getting started with an exercise program? Hoping to improve your existing routines or find new workout options? Did you know that a complete plan consists of three basic elements: aerobic fitness, muscle strength/endurance and flexibility? How do you assess your current fitness level before you begin? How do you know how much exercise you should do, or whether you should see a doctor before you start?
Our Healthy Living channel provides in-depth answers to these questions, along with guidelines to help you develop a fitness program that's right for you. With these exercise and fitness tips, you can learn to gauge how hard and how often you should exercise, and get yourself started on the road to better fitness today.
Q. Why do you use the BMI, and is it useful for weight lifters?
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.
One of the limitations of BMI is that it can overpredict overweight or obesity in people who are lean and muscular. For instance, someone who is 5 feet 10 inches tall and weighs 220 pounds, with 12% body fat, would be considered obese based on BMI standards. Obviously, someone with 12% body fat is not obese.
The scientists who developed the BMI guidelines readily admit to this limitation. But their rationale is that most Americans are not lean and muscular and so for most people, the BMI is an accurate assessment of body fat and increased health risk.
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.
The BMI, for the majority of Americans, is the most up-to-date and scientifically sound method available for determining healthy weight.
Q. Does aerobic exercise interfere with muscle gains from weightlifting?
If you're training for an endurance event like a marathon, when you might run 60 miles or more per week, you'll almost always see a decrease in your muscle mass. For most of us, who do more moderate amounts of physical activity, there will be minimal, if any, loss in muscle mass -- so there's nothing to worry about.
If you do plan on lots of aerobic exercise and are concerned about losing muscle, try starting with 20-30 minutes of moderate aerobic exercise (at 50% to 70% of your maximum heart rate) two to three days per week, and see how it goes.
Q. Should I hold off on weight training until I lose weight?
Absolutely not. 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. Weight lifting 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.
- Building strength helps you feel good about yourself. Although the scale may show a slight weight gain when you start lifting weights (usually five pounds or less), you probably won't look heavier because the gain is in muscle, and your clothes may even fit more loosely.
Q. How much exercise should I do?
In addition to the National Academies' Institute of Medicine's recommendation of 60 minutes of daily exercise to prevent weight gain, there are two other major U.S. guidelines for how much physical activity you need:
- The American College of Sports Medicine recommends a five- to 10-minute warm-up and then 30 to 45 minutes of continuous aerobic activity (such as swimming, biking, walking, dancing, or jogging) three to five times a week, with a stretch and cool down period in the last five to 10 minutes. The ACSM also recommends weight training: at least one set (eight to 12 repetitions) each of eight to 10 different exercises, targeting the body's major muscle groups.
- The surgeon general recommends accumulating 30 minutes of moderate-intensity activity (hard enough to leave you feeling "warm and slightly out of breath") on most, if not all, days of the week. You can do it in two bouts of 15 minutes, three bouts of 10 minutes, or one bout of 30 minutes. This recommendation emphasizes incorporating activity into your daily life -- walking instead of taking the bus, parking your car farther from the mall and walking across the parking lot, taking stairs instead of the elevator, and washing your car by hand.
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Q. I don't have time to exercise. I hate 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.
Both guidelines will help improve your health and fitness. Following the more vigorous ACSM recommendation will make you more aerobically fit, and its strength-training component will make you stronger and more toned. The Surgeon General guideline, meanwhile, may be easier to fit into your lifestyle -- not replacing the ACSM guideline, but complementing it.
If you already exercise vigorously at the gym several times a week, there's no reason to quit. But if the ACSM recommendation is too much for you, the Surgeon General's report offers you an alternative.
The most important thing is that you do something.
Q. 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 farther 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.
Whichever 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 back to what has worked in the past, or use your accomplishments to re-energize yourself.
Q. What should my heart rate be during exercise?
Richard Weil, MEd, CDE, recommends calculating your target heart rate with a formula called the "heart rate reserve" method. Use a watch with a second hand to keep track of how many times your heart beats per minute. You can feel your heartbeat at the underside of your wrist or along the side of your neck.
Here's how to use the formula:
- Determine your Maximum Heart Rate (MHR) by subtracting your age from 220.
- Then, subtract your resting heart rate (it's best to take this when you first wake up in the morning) from your Maximum Heart Rate to find your Heart Rate Reserve (HRR).
- Multiply your HRR by the percentage of your MHR at which you wish to train (60% to 85% is the usual range for people looking to increase fitness and health).
- Add your resting heart rate back to that result to get your target rate.
So, assuming an age of 27, a resting heart rate of 70 beats per minute, and a desired training range of 70%, the calculation would look like this:
220 - 27 = 193
193 - 70 = 123
123 x .70% = 86
86 + 70 = 156
Remember, this is an estimate, not an absolute. Also keep in mind that athletes may exceed the training zone, and even the maximum heart rate, during high-intensity training.
Q. My weight has hit a plateau. What do I do?
There are several reasons why your weight can hit a plateau, including:
- Losing weight too quickly. When this happens, your metabolism (the rate at which your body burns calories) can slow down because your body senses it is starving. Rapid or large amounts of weight loss can slow your metabolism by as much as 40% in six months.
- Losing muscle. When you lose weight, up to 25% can come from muscle tissue. And since muscle is the engine in your body that burns calories and helps maintain your metabolism, losing it can hinder weight loss. Weightlifting can help preserve and build muscle.
- Reaching your body's particular set point -- the weight and metabolic rate your body is genetically programmed to be. Once you reach that point, it's much harder to lose weight and even if you do, you're likely to regain it. If you're at a weight at which you've hit a plateau in the past, if your body generally seems to gravitate toward that weight, and you're within a BMI (body-mass index) range of 20 to 25, then you may be at your set point.
- Decreasing your physical activity and/or increasing your caloric intake. People lose weight all the time by reducing their caloric intake without doing any exercise, but it's almost impossible to keep weight off without exercising. Many scientists agree that physical activity is the single best predictor of whether a person will maintain a weight loss.
- Other health factors, including thyroid or adrenal gland problems; medications like antidepressants; quitting smoking; menopause; and pregnancy.
Even with any of the above factors, the bottom line to losing weight is eating fewer calories than you burn. Studies show that people almost always underestimate how many calories they're eating. So if you're struggling with weight loss, you're still exercising, and you've ruled out any of the above reasons for weight plateaus, look at your calorie intake.
As for exercise and weight plateaus, sometimes a change in routine can help. Instead of the treadmill, try the bike, or the stepper. Instead of a dance class, try a stretch and tone class. If you're not weight lifting, this would be a good time to start. If you already do aerobic exercise, try adding intervals (short bursts of higher-intensity exercise) to your aerobic workouts. And keep reminding yourself that if you maintain an active lifestyle and continue with healthy eating, you will reach your goals.
Q. What's the bottom line to weight loss?
The bottom line to weight loss is to burn more calories than you consume all day. (The behavior isn't simple, but the equation is.) For example, if you eat 2,500 calories a day and only burn 2,000, you gain weight; if you eat 1,500 calories and burn 2,000, you lose weight; if you eat 2,000 and burn 2,000 you maintain weight.
It's true that there are several medical conditions, and medications, that can make weight loss difficult (see below). But even if one of those factors applies to you, you still need to burn more calories than you consume to lose weight.
The good news is this: You can lose weight with a very modest amount of exercise.
People lose weight all the time without exercise by reducing their caloric intake. But keeping the weight off without exercise is another matter. Many experts agree that exercise is the single best predictor of long-term weight control. If you lose weight and don't start exercising, there's a very good chance you will regain it.
Here are some factors that can keep you from losing weight and/or cause weight gain:
- Thyroid or adrenal gland problems.
- Medications like antidepressants.
- Stopping smoking.
- Rapid weight loss. This can lower metabolism because the body senses it is starving and make it harder to lose weight. The decrease in metabolic rate is often due to loss in muscle (when you lose weight, approximately 25% of the loss comes from muscle), so lifting weights is a good idea.
- Menopause (and premenopause).
If you think any of these things are factors for you, your doctor may be able to help.
Otherwise, patience, determination, regular physical activity, and attention to your diet are the keys to long-term weight control. Doing these things will give you your best shot at reaching your weight loss goals and keeping the weight off.
Q. 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 congestive 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 an exercise program.
If you have questions about your condition or are still not sure what exercise you can safely do, please consult your physician.
Q. 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 maximum for one to three minutes. Then, go back to jogging at the 70% heart rate, and continue alternating.
As your fitness improves, your heart rate will be lower at the higher speeds, and then you can spend more time at those speeds. A good starting ratio of work to active rest is 1:3; you can always vary the ratios if they turn out to be too hard or too easy.
I 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.
Q. What's the difference between the fat-burning mode and the cardio mode on the machines at the gym?
There are problems with the fat burning option on the cardio machines, and it really ought to be eliminated.
The idea behind the fat burning option is this: Because fat is denser than carbohydrate, it requires more oxygen to burn. So, to maximize the percentage of fat you burn, compared to carbohydrate, the fat-burning mode would have you work out at a pace at which your body can deliver lots of oxygen to your muscles. That generally means a slow pace, to keep you from getting breathless.
The problem is that when you exercise at a slower speed, you burn fewer total calories -- from both carbohydrate and fat -- because you simply don't do as much work. Further, the way to get aerobically fit is to get your heart rate into the training range (usually 60% to 85% of your maximum heart rate), which is hard to do at slower speeds. And fitness is ultimately what you're after, whether your goals are better health, burning calories, or improving heart and lung capacity.
The bottom line is that the fat burning mode probably won't be intense enough to maximize total calorie- or fat-burning, or to help you increase or maintain optimum fitness levels. Use the cardio mode to maximize your exercise benefits.
Q. What is basal metabolic rate?
Basal metabolic rate (BMR) is the rate at which your body burns calories just to sustain life. For most people, that's roughly 50 to 80 calories per hour, or 1,200 to 1,920 calories per day. Exactly what your BMR is depends on genetics, your muscle mass, and other factors.
Of course, you burn more calories when you exercise -- or just go about the activities of daily life. For example, if you work out at the gym for 60 minutes and burn 400 calories, that comes in addition to whatever your BMR burns up. (If you walk home from the gym instead of driving, you'll burn even more!) At the end of the day, if your total energy expenditure is greater than the number of calories you've eaten, you'll lose weight.
Originally Published May 1, 2003.
Medically updated February 2006.
SOURCE: WebMD Weight Loss Clinic Expert Column WebMD Weight Loss Clinic: Exercise and Fitness by Richard Weil, MEd, CDE, published May 1, 2003. American College of Sports Medicine web site: "Guidelines for Healthy Aerobic Activity."
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