By Mark P. Kelly, Ph.D.
Unless you have been living on an island or mountaintop somewhere (or simply don’t watch television), you’ve undoubtedly seen numerous infomercials talking aboutresting metabolic rate (RMR) and how one exercise or another will increase it, causing body fat to just melt away. Not surprisingly, there are many fallacies about how to measure RMR, how accurate those measurements are, and what particular exercises or diets will affect it. The purpose of this article is to clear up some of the confusion surrounding RMR and its energy expenditure cousins: non-exercise activity thermogenesis (NEAT) and excess post-exercise oxygen consumption (EPOC). We’ll do a quick review of the basics of metabolism, discuss the relative accuracy of different methods and formulas for calculating RMR and cover some tricks of the trade you can use to help your clients raise their RMRs, both acutely and chronically.
What Is Resting Metabolic Rate?
RMR Formulas in Action
Following are sample calculations for a 48-year-old man who is 180 cm (5’8”) and weighs 80 kg (176 lb) using several popular RMR equations.
* Revised Harris-Benedict BMR Equations (calories/day):
Male: (88.4 + 13.4 x weight) + (4.8 x height) – (5.68 x age)
Female: (447.6 + 9.25 x weight) + (3.10 x height) – (4.33 x age)
weight in kilograms, height in centimeters, age in years
Sample: 88.4 + 1072 + 864 – 272.6 = 1,751
* A more accurate formula is the Mifflin-St Jeor Equation(calories/day):
Male: 9.99 x weight + 6.25 x height – 4.92 x age + 5
Female: 9.99 x weight + 6.25 x height – 4.92 x age – 161
weight in kilograms, height in centimeters, age in years
Sample: 800 + 1125 – 236 + 5 = 1,694
Two formulas that consider lean body mass (LBM) include the Katch-McArdle equation (BMR) and the Cunningham equation (RMR). These formulas should be used for more athletic clients, where muscle mass is significantly higher than average. A study (Johnstone et al., 2005) involving 150 adults in Scotland revealed that 62.3 percent of the variations seen in BMRs are related to fat-free mass (bone, tissue, muscle).
* Katch-McArdle (BMR)(calories/day):
370 + (21.6 x LBM)
To calculate LBM, multiple total body weight by body-fat percentage. If our sample client has 10 percent body fat and weighs 80 kg, his LBM would be 72 kg (i.e., body weight of 80 kg – 10 percent body fat of 8 kg = 72 kg of LBM). Therefore, using the Katch-McArdle equation:
370 + (21.6 x 72) = 1,925
Note that this result is significantly higher than the non-LBM formulas (i.e., revised Harris-Benedict and Mifflin-St Jeor equations).
* Cunningham: RMR (This formula is similar to Katch-McArdle, but provides a slightly higher estimate.)
500 + (22 x LBM)
500 + (22 x 72) = 2,084
Metabolic processes in the body require energy and are comprised of anabolic processes, which build up tissues, and catabolic processes, which break down tissues and fuel sources for energy. The rate at which these processes occur is measured in calories per unit of time, and is most often given in calories per day.
The term basal metabolic rate (BMR) is often confused and/or interchanged with RMR or resting energy expenditure (REE). Basal metabolic rate, however, can only be found during an awake, but totally rested and post-absorptive state, and in a neutrally temperate environment. Thus, it is quite restrictive and only used in clinical or laboratory settings. The total amount of calories an individual burns in a given day is known as total daily energy expenditure (TDEE) and it comes from several sources including RMR, the thermogenic effect of food (TEF), non-exercise activity thermogenesis (NEAT), excess post-exercise oxygen consumption (EPOC) and, of course, exercise (Ex).
TDEE = RMR + TEF + NEAT + EPOC + Ex
RMR and TEF are relatively constant, with minor fluctuations due to muscle mass and conditioning, and to dietary shifts, respectively. The NEAT and exercise components have large variability and can greatly influence one’s total caloric expenditure.
How Do I Calculate RMR?
There are two main ways to determine how many calories you or your client burns in a given day. A relatively accurate (but more difficult) method is called indirect calorimetry, which uses expired gases to calculate the amounts and types of fuel being utilized. The Weir equation below can be used to calculate the number of calories burned per minute. Thus, to work it up to a full 24-hour day, simply multiply the total by 1,440. The respiratory quotient (RQ) is helpful in determining what type of fuel is being catabolized for energy. RQ values are typically in the mid-70s when an individual is at rest; this figure will increase to the 90s as activity level increases. Popular devices such as the BodyGem utilize respiratory gases and the Weir equation for a more accurate metabolic-rate determination.
Abbreviated Weir Equation:
REE = [3.9 (VO2) + 1.1 (VCO2)] 1.44
VO2 = volume of oxygen uptake (mL/min)
VCO2 = volume of carbon dioxide output (mL/min)
Respiratory quotient (RQ) = VCO2/VO2
- fat 0.70
- underfeeding <0.71
- protein 0.80
- mixed energy 0.85
- carbohydrate 1.00
- fat storage >1.00
- ketosis <0.70
A less accurate, but much easier, method for determining RMR is to use one of several different formulas (see sidebar, "RMR Formulas in Action"). Keep in mind, however, that some sources claim these formulas can be off by as much as 1,000 calories, with the majority of error or variation occurring in the calculation of daily energy expenditure. Several websites, including
Health-calc, make it possible to more accurately record daily activity, which can increase the accuracy of the RMR calculation.
