Why test for metabolic rate?
A metabolic assessment measures several things:
- The amount of calories your body needs to function, including everything from regulating your body’s hormones to thinking the thoughts that run through your mind
- The amount of calories you need to consume each day to achieve your fitness goal, whether that’s weight loss goal or greater athletic performance
All that information comes from measuring your heart rate and from evaluating the mix of oxygen and carbon dioxide in your breath. Those measurements are taken at various levels of activity, from a point of complete rest to a point just shy of your highest normal physical activity level.
The resting metabolic rate (RMR) is the amount of energy someone burns per unit time. This rate is known as the calories per day and it is measured under resting conditions. There are formulas such as the Harris-Benedict formula which can approximate it based on your age, gender, height, and body weight; however, this calculation can be as much as 20% off!
Women
661+ (4.38* wt [lbs]) + (4.38 * ht [in]) - (4.7 * age) = RMR
Men
67 + (6.24 * wt [lbs]) +(12.7 * ht [in]) - (6.9 * age) = BMR
The best way to measure the RMR is by a method called indirect calorimetry. This method measures the oxygen utlized and carbon dioxide produced to determine the type of fuel being catabolized (used by the body) and the rate it is being used up at. So, by getting a stable resting level, one can assume that this is the rate of usage or how many calories the body uses just to maintain a resting state.
This RMR is absolutely critical to someone trying to lose weight because they can adjust both their activity and calorie intake to the appropriate level to lose weight.
Activity Multiplier - to calculate EER
(EER - estimated energy requirements)
Sedentary 1.15 factor
Light Activity (normal daily living activity- desk job) 1.3 factor
Moderately Active (exercises 3-4x/ wk) 1.4 factor
Very Active (exercises 5-6x/ wk) 1.6 factor
Extremely Active (exercises more than 6x/ wk) 1.8 factor
Also, the greater the muscle mass the greater the RMR. The fat mass also affects the RMR but nowhere near as much as muscle. It is believed that
a pound of muscle burns about 30-50 calories per day. This does not sound like much but look at the numbers. Abbreviations: Calories per day-(cal/d) muscle-mm
Let's look at the numbers if someone was able to maintain just 5 pounds of muscle across a year and do no more activity than normal and of course not eat more.
Assuming the 50 cal/d number: 5 lbs * 50 cal/lb mm/day = 250 cal/d. Doesn't sound like much, but take it across a whole year - (365 d)= 91,250 cal/ yr.
When you divide how many calories it takes to burn off a pound of fat= 3500 then;
91,250/ 3500 = 26.07 lbs of fat being burnt with out moving a muscle - just gaining muscle!!
So, during most diets people lose muscle mass which is critical toward long term weight loss. Many experts believe resistance exercise is much more important than aerobic exercise for weight loss.