Motor, thermal and sensory factors in heart rate variation: a methodology for indirect estimation of intermittent muscular work and environmental heat loads.

In experiments where the effects of other influencing factors are removed, heart rate depends mainly upon the mechanical work performed and upon the environmental heat stress imposed. Their respective influences can be conveniently estimated by an appropriate partition of the heart rate values recorded at one minute intervals. The thermal component of the heart rate is a function of rectal and mean skin temperatures, while its motor component is a function of the mechanical power developed during muscular exercise, both components acting cumulatively on the heart rate The partition procedure developed on an experimental basis was worked into a practical method for estimating the thermal stress and the muscular work stress from continuous records of the heart rata in actual work situations, the subjects having been previously calibrated for their circulatory responses to work and heat during standard tests in a climatic chamber. Control experiments were conducted to demonstrate the validity of the method i...