Related Resources: calculators

Metabolic Rate Energy Burned Calculator

Heat Transfer Engineering
Thermodynamics
Physics

Metabolic Rate Energy Burned Calculator and Formulas for Humans

When metabolic rates must be determined more accurately than is possible with tabulated data, physiological measurements with human subjects may be necessary. The rate of metabolic heat produced by the body is most accurately measured by the rate of respiratory oxygen consumption and carbon dioxide production. An empirical equation for metabolic rate is given by Nishi (1981):

Eq. 1
M = 567 ( 0.23 RQ + 0.77) Q_O2 / A_D

where

M = metabolic rate, Btu/h·ft²
RQ = respiratory quotient; molar ratio of Q_CO2 exhaled to Q_O2 inhaled, dimensionless
Q_O2 = volumetric rate of oxygen consumption at conditions (STPD) of 32°F, 14.7 psi, ft³/h
A_D = Activity metabolic rates Btu/h·ft² (met), typical metabolic rates for an average adult
(A_D = 19.6 ft²) for activities performed continuously. see: Metabolic Rate Thermal Energy Created by the Human Body

The exact value of the respiratory quotient RQ depends on a person’s activity, diet, and physical condition. It can be determined by measuring both carbon dioxide and oxygen in the respiratory airflows, or it can be estimated with reasonable accuracy.

A good estimate for the average adult is RQ = 0.83 for light or sedentary activities (M < 1.5 met), increasing proportionately to RQ = 1.0 for extremely heavy exertion (M = 5.0 met). Estimating RQ is generally sufficient for all except precision laboratory measurements because it does not strongly affect the value of the metabolic rate: a 10% error in estimating RQ results in an error of less than 3% in the metabolic rate.

A second, much less accurate, method of estimating metabolic rate physiologically is to measure the heart rate. Table 1 shows the relationship between heart rate and oxygen consumption at different levels of physical exertion for a typical person. Once oxygen consumption is estimated from heart rate information, Equation (1) can be used to estimate the metabolic rate. Other factors that affect heart rate include physical condition, heat, emotional factors, and muscles used. Astrand and Rodahl (1977) show that heart rate is only a very approximate measure of metabolic rate and should not be the only source of information where accuracy is required.

Table 1 Heart Rate and Oxygen Consumption at Different Activity Levels

Level of Exertion	Heart Rate, bpm	Oxygen Consumed, ft3/h QO2
Light work	<90	<1
Moderate work	90 to 110	1 to 2
Heavy work	110 to 130	2 to 3
Very heavy work	130 to 150	3 to 4
Extremely heavy work	150 to 170	>4

Accuracy: Estimating metabolic rates is difficult. Values calculated as well as those given in the webpage Metabolic Rate Thermal Energy Created by the Human Body indicate metabolic rates only for the specific activities listed. Some entries give a range and some a single value, depending on the data source. The level of accuracy depends on the value of M_act and how well the activity can be defined. For well-defined activities with M_act< 1.5 met (e.g., reading). For values of Mact > 3, where a task is poorly defined or where there are various ways of performing a task (e.g., heavy machine work), the values may be in error by as much as ±50% for a given application. Engineering calculations should thus allow for potential variations.

Conversions

1 met = 18.4 Btu/h· ft² = 50 kcal/h ·m².

Related

• Metabolic Rate Thermal Energy Created by the Human Body
• How much oxygen does the human lung consume?

Source

2016 ASHRAE Handbook - HVAC Systems and Equipment, ASHRAE: 2016.