American Journal of Clinical Nutrition, Vol 24, 1126-1138, Copyright © 1971 by The American Society for Clinical Nutrition, Inc.

The indirect measurement of energy expenditure in industrial situations

¹ From the Haskell Laboratory for Toxicology and Industrial Medicine, E. I. du Pont de Nemours and Company, Wilmington, Delaware 19898

The rate of oxygen consumption, preferably by the open-circuit technique, is recommended for measuring the severity of the work load, i.e., the work stress, imposed on the worker. This is especially true if the work load is to be graded in comparison with other types of work. When necessary, one of the two abbreviated methods for measuring oxygen consumption may be used. The determination of both the oxygen concentration and minute volume of the expired air provides an accurate estimate of energy expenditure if the liters of oxygen are converted to kilocalories, when the subject is in a steady state. The simplest method, estimation from the minute volume of the expired air, requires calibration of the subject if reliable data are to be obtained for an individual. On the other hand, there is evidence that estimates, based on data obtained on a number of individuals, may be useful for many industrial operations.

An alternative to the measurement of oxygen consumption, the measurement of the heart-rate response, is valid only when the total stress is due to the work load. Since the strain induced by the work, and consequently the heart-rate response, varies from individual to individual, calibration of the individual subject is mandatory.

In contrast, if it is the strain due to work that is to be investigated, heart-rate measurements are recommended. The effect of the operation on the worker under the conditions existing at the time of measurement can be determined, and if the strain is considered to be excessive, steps can be taken to alleviate the situation. Although measurement of the heart rate during both work and recovery is to be preferred, in situations where observations must be kept minimal, careful measurements of the recovery pulses, P₁, P₂, and P₃, will provide the information necessary to determine whether the operation and the environmental conditions, or both, should be modified.