You use energy no matter what you’re doing, even when sleeping. The BMR Calculator will calculate your Basal Metabolic Rate (BMR); the number of calories you’d burn if you stayed in bed all day. The BMR formula uses the variables of height, weight, age and gender to calculate the Basal Metabolic Rate (BMR). This is more accurate than calculating calorie needs based on body weight alone. The only factor it omits is lean body mass and thus the ratio of muscle-to-fat a body has. Remember, leaner bodies need more calories than less leaner ones. Therefore, this equation will be very accurate in all but the very muscular (will underestimate calorie needs) and the very fat (will over-estimate calorie needs).
Your basal metabolic rate, or BMR, is the minimum calorific requirement needed to sustain life in a resting individual. It can be looked at as being the amount of energy (measured in calories) expended by the body to remain in bed asleep all day!
BMR can be responsible for burning up to 70% of the total calories expended, but this figure varies due to different factors (see below). Calories are burned by bodily processes such as respiration, the pumping of blood around the body and maintenance of body temperature. Obviously the body will burn more calories on top of those burned due to BMR.
BMR is the largest factor in determining overall metabolic rate and how many calories you need to maintain, lose or gain weight. BMR is determined by a combination of genetic and environmental factors, as follows:
• Genetics. Some people are born with faster metabolisms; some with slower metabolisms.
• Gender. Men have a greater muscle mass and a lower body fat percentage. This means they have a higher basal metabolic rate.
• Age. BMR reduces with age. After 20 years, it drops about 2%, per decade.
• Weight. The heavier your weight, the higher your BMR. Example: the metabolic rate of obese women is 25% higher than the metabolic rate of thin women.
• Body Surface Area. This is a reflection of your height and weight. The greater your Body Surface Area factor, the higher your BMR. Tall, thin people have higher BMRs. If you compare a tall person with a short person of equal weight, then if they both follow a diet calorie-controlled to maintain the weight of the taller person, the shorter person may gain up to 15 pounds in a year.
• Body Fat Percentage. The lower your body fat percentage, the higher your BMR. The lower body fat percentage in the male body is one reason why men generally have a 10-15% faster BMR than women.
• Diet. Starvation or serious abrupt calorie-reduction can dramatically reduce BMR by up to 30 percent. Restrictive low-calorie weight loss diets may cause your BMR to drop as much as 20%.
• Body Temperature/Health. For every increase of 0.5C in internal temperature of the body, the BMR increases by about 7 percent. The chemical reactions in the body actually occur more quickly at higher temperatures. So a patient with a fever of 42C (about 4C above normal) would have an increase of about 50 percent in BMR.
• External temperature. Temperature outside the body also affects basal metabolic rate. Exposure to cold temperature causes an increase in the BMR, so as to create the extra heat needed to maintain the body’s internal temperature. A short exposure to hot temperature has little effect on the body’s metabolism as it is compensated mainly by increased heat loss. But prolonged exposure to heat can raise BMR.
• Glands. Thyroxin (produced by the thyroid gland) is a key BMR-regulator which speeds up the metabolic activity of the body. The more thyroxin produced, the higher the BMR. If too much thyroxin is produced (a condition known as thyrotoxicosis) BMR can actually double. If too little thyroxin is produced (myxoedema) BMR may shrink to 30-40 percent of normal. Like thyroxin, adrenaline also increases the BMR but to a lesser extent.
• Exercise. Physical exercise not only influences body weight by burning calories, it also helps raise your BMR by building extra lean tissue. (Lean tissue is more metabolically demanding than fat tissue.) So you burn more calories even when sleeping.
• Underweight = <18.5
• Normal weight = 18.5–24.9
• Overweight = 25–29.9
• Obesity = BMI of 30 or greater
BMI = weight in lbs. times 4.88 divided by height in feet squared. Here is an example for a person weighing 172 lbs. and who is 6 feet 1 inch tall: BMI = (172 X 703) ÷ (73 X 73) = 120916 ÷ 5329 = 22.7 rounded to a single decimal.
The physical activity level is defined for a non-pregnant, non-lactating adult as that person’s total energy expenditure in a 24-hour period, divided by his or her basal metabolic rate (BMR):
The physical activity level can also be estimated based on a list of the (physical) activities a person performs from day to day. Each activity is connected to a number, the physical activity ratio. The physical activity level is then the time-weighted average of the physical activity ratios.
The following table shows indicative numbers for the Physical activity level for several lifestyles:
Calculate Target Heart Rate (THR)
1. Subtract your age from 220. This will give you your maximum heart rate in beats per minute.
2. Multiply that number by .60 to get 60 percent of your maximum heart rate and then by .80 to get 80 percent of your maximum heart rate.
3. This range will give you your target heart rate zone. For example, Jenny is 30 years old. To determine her maximum heart rate we will:
Subtract 30 from 220, which gives us 190 Multiply 190 x .60, which equals 114 Multiply 190 x .80, which gives us 152. While walking, Jenny should ensure that her heart rate is between 114 and 152 beats per minute.
Check your pulse several times throughout your walk to be sure you are staying with in the zone. Beginner walkers should stay close to the lower range of the target heart rate zone until they feel comfortable and ready for a more intense walk.
How to Take Your Pulse
Now that you can calculate target heart rates, you’ll need to know how to find yours. To determine your resting pulse rate, take your pulse in the morning when you are the most relaxed. Sit quietly in a chair. You will notice that your resting pulse rate will get lower as you become more fit.
You can measure your pulse rate anywhere an artery comes close to your skin, but it is recommended locating it in the following locations:
1. Lightly place two fingers on the inside of your wrist, just below the base of your thumb. Never use your thumb to take your pulse because it has its own pulse. Count the number of beats for 30 seconds and then multiply by 2 to determine the number of beats per minute.
2. Gently place two fingers on your neck, on either side of your windpipe. This is your carotid artery, which carries blood to your head. Do not press too hard as you could restrict the blood flow to your head, which could cause you to become lightheaded or faint. Count the number of beats for 30 seconds and then multiply by 2 to determine the number of beats per minute.
Knowing your body fat percentage can also help you determine if your weight loss goals are realistic. Remember, weight loss doesn’t always mean fat loss.
For example, let’s say you are a 130 pound woman with 23% body fat, and your goal is to lose 20 pounds.
As you can see, the goal of losing 20 pounds is not realistic or healthy. At 110 pounds, this woman still requires 100 pounds of lean body mass, but would only be carrying 10 pounds, or only 9% body fat. From the body fat chart above, you can see that this is a dangerously low percentage.
A better goal might be for the woman to reduce her body fat from 23% to 18%. In this case:
So, for this individual to achieve a lean, but healthy 18% fat, she would need to lose only 7 pounds of fat, reducing her weight from her current 130 pounds to 123 pounds. Losing more than 7 pounds means losing lean body mass (usually metabolically-active muscle tissue), which is clearly not desirable. So before you decide that you need to “lose weight”, remember to consider that “weight” consists of both lean body mass and body fat. Try to keep your weight loss goals realistic, and remember, keep the calorie-burning muscle, and lose only the fat.