Calculating Metabolic Rate
The International Sports Sciences Association (ISSA) defines metabolism as “the total of all the chemical and physical processes by which the body builds and maintains itself (anabolism) and by which it breaks down its substances for the production of energy) catabolism. Metabolic rate is how much energy an individual expends and is measured in calories.
Maintaining weight is more than balancing calories consumed with calories expended. But, it helps to have an idea how many calories your body is burning. Determining your metabolic rate requires knowing your resting metabolic rate or RMR, and quantifying how physically active you are ranging from sedentary to extremely active and everything in between.
Calculating Resting Metabolic Rate
To calculate your resting metabolic rate you need to know four things; how much you weigh, your height, your age and your activity level. Most people know those four things.
Step 1: (Weight in pounds divided by 2.2) times 10
Step 2: (Height in inches times 2.54) times 6.25
Step 3: (Age times 5) plus 5
Here’s what this looks like for a 50 year old male who weighs 220 pounds, is 5 foot 10 inches tall, and is moderately active.
Step 1: (220 pounds divided by 2.2 = 100) times 10 = 1000
Step 2: (70 inches times 2.54 = 177.8) times 6.25 = 1111
Step 3: (50 years old times 5 = 250) plus 5 = 255
1000 + 1111 – 255 = 1,856 calories or resting metabolic rate. This is the number of calories our 50 year old male would burn if he did nothing all day but lay around.
To determine his overall metabolic rate we need to know his activity level and mulitply his RMR with the cofactor that corresponds to his activity level.
- Sedentary: little or no exercise cofactor is 1.2
- Lightly active: light exercise 1-3 days a week cofactor is 1.37
- Moderately active: moderate exercise 3-5 days a week cofactor is 1.55
- Very active: hard exercise 6-7 days a week cofactor is 1.72
- Extremely active: twice daily exercise cofactor is 1.9
So for our 50 year-old male who is moderately active his overall metabolic rate is 1,856 (his RMR) times 1.55 which equals 2,877 calories per day. This is a reasonably close approximation and can be used to determine the needed caloric intake to maintain, gain, or lose weight. Muscle is more metabolically active than fat, about 2-3 times more active, and that is not taking into account with this equation.