Your BMR and what you can do about it: your body burns calories all the time. Here's how your body can burn more of them.

Your basal metabolic rate--otherwise known as your BMR--is the rate at which you burn calories at rest just to maintain vital body functions. These functions include breathing and heartbeat and brain activity, among others. Your BMR usually accounts for at least half of the calories you burn in a day. So now you'll want to know what a typical BMR is for someone of your height and weight.

"A typical BMR for women is 1200-1700 kilocalories/day; for men, more like 1400-2100," says Michael Jensen, M.D., an endocrinologist at the Mayo Clinic. BMR can be measured when a person is lying in bed without moving and has not eaten for at least eight hours. Whether you are active or sedentary, this is how the true BMR is measured. Compute your own BMR (see page 19), but remember that the normal range is wide to accommodate all the variables that help to determine a person's BMR.

"The Harris-Benedict is a standard formula for computing BMR," says Jensen, M.D. "One needs age, gender, height, and weight to get BMR with the Harris-Benedict, and it's accurate to within 10 percent about 80-90 percent of the time."

The Variables

"For 90-plus percent of the people we test who think they have low metabolism, it's pretty normal," says Jensen. "It's actually only a tiny fraction of people who burn fewer calories at rest than they should according to their height, weight, and age."

People tend to overemphasize the impact that cutting calories will have. At the same time, they don't take into account a sedentary lifestyle. Here are factors that determine your BMR.

* Height

* Weight

* Age

* Sex

* Activity level

* Recent food intake

* Environmental temperature

* Emotional state

* Pregnancy

* Menstruation 

* Level of thyroid hormones 

* Stress hormones, such as epinephrine and norepinephrine 

What You Can't Change

Let's say you are a 32-year-old female, five feet, five inches tall and 154 pounds. Three out of those four variables are given to you; you cannot change age, sex, and height. However, everything else on the list can vary. Pregnancy is temporary and so is menstruation, though it lasts an average of 30 to 40 years.

"The decrease in BMR with age is a continuum and generally has the greatest decline after age 50, mostly through the loss of lean tissue, or muscle," says Scott K. Powers, Ph.D., Ed.D., director for the Center for Exercise Science at the University of Florida. Much of this decline is the result of a loss of lean tissue, such as muscle, so even the inevitable decline in BMR because of age can be slowed by staying active and maintaining or building muscle, or lean body mass (LBM). Strength training with weights or machines will help build LBM, and should be part of a good fitness program.

People who have a high ratio of LBM to fat will burn more calories all of the time, even at rest. Men tend to have a higher BMR than women because they have more LBM. So being male is an advantage when it comes to burning calories. However, women who are in good physical shape will have more LBM and a higher BMR than women who live a sedentary lifestyle.

Rev It Up

Body weight can fluctuate greatly. So the best thing you can do to control your weight and raise your metabolism is to achieve and maintain a desirable weight through a combination of exercise and controlled food intake. Aerobic activities, such as running, brisk walking, biking, and climbing, are great calorie burners.

"But remember that body weight isn't everything. We have a society fixated on weight," says Eric Hanson, M.D. "If you are in good physical shape, your cardiovascular risk is lowered, and so is your risk of contracting cancer."

Your activity level also bears strongly on BMR. The more sedentary your lifestyle, the closer to your BMR your actual calorie burn for a day is. A low BMR does not give you much flexibility on caloric intake. Remember that all activity counts, including walking the dog, vacuuming, and climbing the stairs at work instead of taking the elevator.

You use only about 10 percent of the calories you consume to digest your food. But high-fiber foods--such as whole grains, fruits, and vegatables--take more effort to digest and therefore burn more calories during processing than a slice of cheese or a cookie.

Your BMR is like a thermostat in a house, so it can change according to the demands placed on it. Keeping your house or apartment a degree or two cooler can affect metabolism, because you will burn more calories to stay warm.

"Think of it in terms of having a fever," says Hanson, former U.S. Navy diving medical officer and current chief resident for the Department of Dermatology at the University of North Carolina, Chapel Hill. "Your body revs up to fight an infection, so you are burning more energy."

Your emotional state and the level of stress in your life can also impact the rate at which you burn calories. Stressful situations, such as illness, divorce, the death of a person close to you, a difficult job, or loss of your job, can raise your BMR. You may lose weight and not know why.

For a small minority of people who cannot seem to lose weight and keep it off, the thyroid gland may he the culprit. Slow metabolism can be caused by hypothyroidism, a condition caused by insufficient production of thyroid hormones. The opposite of this, hyperthyroidism, results in too much hormone being secreted. Your doctor can check you for these conditions with a blood test.

Burn, Baby, Burn

The person who is active physically will have a higher BMR, burn more calories, and therefore be able to eat more. Here are some big calorie-burners to bring that BMR up and give you some flexibility in your food intake. Thirty minutes of any combination of these activities three or more times a week will get you in shape. The amount of calories burned are based on a 155-pound male.

* Aerobics--175

* Cycling, vigorous--350

* Running 6 mph--350

* Swimming, moderate--210

* Tennis--245

* Weight Training--210

* Walking 4 mph--158

Everyday Activities Make a Difference

Don't forget that all physical activity counts. Add some of the following to your daily life to help you raise that BMR. For example, a person weighing 154 pounds can lose the indicated number of pounds a year just by performing these activities:

* Walk 10 minutes, 5 days/week, lose 4 pounds

* Climb the stairs at work, 5 minutes, 5 days/week, lose 2 pounds

* Ride stationary bike 10 minutes, 5 days/week, lose 5 pounds

* Clean house 15 minutes, 3 days/week, lose 2 pounds

* Bicycle to errands 20 minutes, 1 day/week, lose 2 pounds

* Play actively with kids 15 minutes, 7 days/week, lose 7 pounds

And Everything Helps

If you have a speaker phone or cordless phone, get up and walk around during those calls. Do you spend a lot of time in airports? Walk, don't sit! Don't use the drive-through; park the car and go inside the bank. Use a push mower instead of a power mower. Wash your car and then wax it. Waxing the car provides a super upper body workout and really burns calories. Plant and tend a garden. Walk during your break at work.

The list goes on, so your weight gain doesn't have to.

Here's the formula for those of you who are keeping score at home:

FOR WOMEN:

655 + (4.36 x weight in pounds) + (4.32 x height in inches) - (4.7 x age) = BMR

FOR MEN: 66 + (6.22 x weight in pounds) + (12.7 x height in inches) - (6.8 x age) = BMR

RELATED ARTICLE: Improve Fitness Without Investing Time or Money.

by Larry Bradford

Losing muscle tone and aerobic capacity because you can't find time to work out? Improve your fitness without spending time or money by altering a few everyday activities.

1. Build your biceps while sitting at your desk. Each time you sit, put your hands above your knees with palms up. While remaining seated, press against the underside of the desktop and lift with as much force as you can without raising your desk off the floor. Continue for a count of 10.

2. Flatten your stomach while driving your car. Don't let your body slouch while driving. Suck in your stomach. Pull your belly button toward your spine. Hold it for a count of 10. Repeat this process every time you turn a corner, or each time a new tune comes on your radio or cd.

3. Add to aerobic capacity in the parking lot. When you drive to the mall or the grocery store, park in a remote area of the parking lot and walk (added benefit: fewer dings in your car from other car doors).

4. Strengthen your triceps and forearms with your phone calls. After each phone call, with palms facing each other, hold the phone horizontally with a hand on each end. Try to push the mouthpiece and the earpiece together. Hold the force of this push for a count of 10.

5. Strengthen your quadriceps and glutes by walking the stairs. When going to your office or apartment, walk from the ground floor to the third floor for a week. Add an additional floor each week until you are walking 6 levels each day. Continue climbing 6 levels daily. (If you really get into this, add a level each week until your boss complains that you are late for work!)

6. Improve balance and strengthen your lower legs while putting on your socks. Balance on one leg and raise the other foot until your quadricep is parallel to the floor. While bending at the waist, use both hands to put a sock on your raised foot. Reverse legs and repeat while putting on the other sock. To gain additional benefit, remain standing on each leg for 30 seconds after the sock is on your foot.

7. Improve your blood circulation while watching TV. When you want to adjust the volume or change channels don't use the remote control. Instead, walk to the TV to make the adjustment. (TV commercials are long enough that you'll have time for 10 push-ups or crunches before returning to your seat!)

8. Stretch your hamstrings each morning before getting out of bed. While lying flat on your back with your legs outstretched, raise one leg. Keep the leg straight and grasp your calf with both hands. Gently pull your leg toward your head until it feels tight but not painful. Hold this position for a count of 20. Repeat this process with the other leg.

In addition to the benefits listed, these activities will burn up calories and assist in reducing that waistline. You'll feel better physically and feel better about yourself.

Larry Bradford writes on health issues from Minneapolis, Minnesota.

Sherry Ballou Hanson writes on health issues from Brunswick, Maine.