Calculating RMR (Without a Lab)

A person’s basal metabolic rate (BMR) and resting metabolic rate (RMR) represent the total amount of energy the body consumes while at rest or asleep. One of the main purposes for determining these rates with respect to fitness is to help calculate a person’s basic caloric needs each day.

 

The Heat Is On

The term “thermogenesis” refers to the measure of total energy exhausted as heat disposal. With age comes a decrease in BMR that is associated with the amount of a person’s lean body mass. However, improving a person’s level of fitness by maintaining or building lean mass can act to counter the body’s tendency to gradually decrease the amount of calories it uses to function. Research has shown that aerobic activity alone doesn’t correlate with an increase in BMR, but anaerobic activity does, and this has been associated with maintaining lean body mass.

The Basal Metabolic Rate (BMR), also referred to as Resting Metabolic Rate (RMR), refers to the amount of caloric consumption by the body during periods of absolute inactivity while in a waking state. That is, it is the energy used for the necessary function of vital organs and processes. Another way to the think of it is that is akin to the number of calories a person would use if he or she remained in bed for a whole day. One way of determining an individual’s BMR is by measuring the oxygen and CO2 exchange that occurs during respiration. This specialized, clinical equipment is not at most people’s disposal. In a clinical setting, BMR measurements are typically taken after a person has woken from 8 hours of sleep and 12 hours of fasting as a means of ensuring that the digestive system is inactive, which itself consumers energy. RMR measurements can be taken with less restricted – and less controlled – conditions, such as not requiring that the person spend the night sleeping in a testing facility.

So, for the purposes here, we will later discuss an alternative method of estimating RMR using a simple formula combined with observation-based body-typing. Since only metabolically active lean tissue is the basis of RMR, it is necessary to determine a person’s total lean mass before any RMR calculation can be used.

There are several ways to measure lean weight and fat weight. These include skin-fold testing, bio-impedance, underwater weighing, etc. Use methods at your disposal, or that you trust the most. Subtract the fat weight from the total weight to arrive at a lean weight (*in some cases, it may be better to estimate lean weight). You now have a lean weight number to fit into a formula. While there are different formulas in common use, they are only marginally more accurate than this simplified version:

Lean Weight x 11 = RMR

Daily Activities

The activities we perform each day – their nature, length, and intensity – can vary considerably from individual to individual. We might expect a construction worker, for example, to expend more calories than a call center representative, on an average day on the job for either one. Because of this, it is useful to take a closer look at a person’s typical physical activities in determining how to provide the body with enough calories to fuel the body and the mind.

An average adult’s daily caloric expenditures can range between 250 calories (sedentary) upwards of 1,000 calories (fairly active), depending mainly again upon the type and amount of work performed.

Body-Typing

In addition to an estimated RMR and daily caloric expenditures, as mentioned, body-typing is required to estimate a person’s daily caloric needs. Some people innately consume energy faster than others (ectomorph), and may need even more calories than described above. On the other hand, if someone tends to burn calories slower than most people (endomorph), he or she may need to consume even fewer calories than mentioned above.

There are three basic body-types: Ectomorph, Mesomorph, and Endomorph.

Ectomorph

The Ectomorph body-type has a small bone structure. Such people can be described as frail and lean. The Ectomorph often complains about difficulty gaining weight, regardless of high caloric intake. The RMR for the Ectomorph will be somewhat higher than the other two body-types of similar lean weight. This body-type burns significantly more calories throughout the day than the other two. If you consider yourself to be an Ectomorph, your caloric need for daily expenditures alone may end up being as much as 1,000 calories more than the Mesomorph and possibly as high as 2,000 calories over the Endomorph’s intake (*provided that all individuals discussed are performing the same type of daily activity). As an Ectomorph, begin by adding at least 1,000 calories to your RMR for daily expenditures and 500 calories/hr for resistance training expenditures.

Those calculations should appear as follows.

Ectomorph’s Lean Weight x 11 = RMR + 1,000 to 1,500 CAL (Daily Activity) + 500 CAL/HR (Weight Training) = Weight Maintenance Intake

Mesomorph

The Mesomorph body-type has a strong bone structure, is muscular, and has what would be considered an average metabolism. The RMR will be average — lower than the Ectomorph, but higher than the Endomorph (assuming all are approximately the same lean weight). For a Mesomorph, start by adding at least another 500 calories (average person’s typical daily activity need) to your RMR for daily expenditures, and 500 calories/hr for resistance training expenditures.

Mesomorph’s Lean Weight x 11 = RMR + 500 to 1,000 CAL (Daily Activity) + 500 CAL/HR (Weight Training) = Weight Maintenance Intake

Endomorph

The Endomorph body-type has a somewhat heavier bone structure than both other types. Such people generally have a body weight that is on the heavy side with tendencies to gain weight easily. The RMR of the Endomorph will be lower than the other two (all of approximately the same lean weight). As an Endomorph, start by adding no more than 250 calories to your RMR for daily activity expenditures, and add 500 calories/hr for resistance training expenditures.

Endomorph’s Lean Weight x 11 = RMR + 250 to 500 CAL (Daily Activity) + 500 CAL/HR (Weight Training) = Weight Maintenance Intake

*All individual suggestions are made with the intention of maintaining a current weight. All individuals are advised to monitor lean and fat weight, making additions and reductions from calories based on goal oriented re-evaluation results along the way.

References

1. Åstrand, Per-Olof, ed. Textbook of work physiology: physiological bases of exercise. Human Kinetics, 2003.

2. The National Federation of Professional Trainers. Personal Trainer Certification Manual. 2nd Ed. Lafayette, IN: NFPT, 2006.