Interindividual variability of human thermoregulation: Toward personalized ergonomics of the indoor thermal environment

Abstract

Objective: The study was undertaken to show the magnitude of interindividual differences in energy expenditure (i.e., heat production) under normal living conditions with the aim of providing physiological evidence to support the advancement of a personalized thermal conditioning approach.Methods: Three sets of experimental protocols with six participants were conducted at neutral and mild cold temperatures. Energy expenditure, local skin temperatures, and core body temperature were measured continuously, while cognitive performance and thermal sensation were surveyed intermittently. The protocols were designed to study the effects of several normal day activities, low-level physical activity and eating a meal, on metabolic and physiological parameters.Results: Large interindividual differences among the subjects were demonstrated using non-normalized data by design. The resting metabolic rate difference was 58%, the percentage change in energy expenditure during standing compared to sitting was up to 31%, and the difference in mechanical work efficiency between the least and the most efficient individual was 39.1%. Energy expenditure increase due to the meal effect was 11.2% to 23.3% at neutral and 9.9% to 33.9% at mild cold temperatures across individuals.Conclusions: Large interindividual differences in metabolic rate under typical everyday living and office activities suggest facilitating personalized thermal conditioning instead of providing uniform temperature. Therefore, it is necessary to find noninvasive markers that can be easily measured and used as surrogates for human heat production to individualize the climate control of buildings.

Quantifying physical activity energy expenditure based on doubly labelled water and basal metabolism calorimetry: what are we actually measuring?

“…Recent measures of TEE in relation to external ambient temperature suggest no relationship for people living in the USA [17 ▪ ] verifying the effectiveness of these strategies in modern societies. Still, exposure to cold (and possibly, to heat) reliably increases metabolic rate, even in the absence of shivering [18]. For people living in cold or hot environments, particularly those who spend considerable time outdoors and those without access to heating or air conditioning, thermoregulation costs will contribute to TEE but not BEE [19 ▪ ].…”

“…The doubly labelled water method provides such an approach, enabling the measurement of average total daily energy expenditure in real-world settings over a 7-day to 14-day period. Participants ingest (or generally in animals have injected) water that is enriched in deuterium ( 2 H 2 O) and oxygen-18 (H 2 18 O). These isotopes reach equilibrium in the body water pool in humans within approximately 4 h. Over subsequent days, both isotopes are eliminated as water leaving the body (urine, sweat, faeces, insensible water loss).…”

Study on thermal health and its safety management mode for the working environment

“…Thermal health refers to the body’s immediate response to ambient environmental heat stress, with its definition rooted in the interplay between the intensity of environmental heat stress and the body’s thermoregulatory abilities ( 35 ). A thermal health environment denotes a thermal environment where workers are maintained in a thermal health state ( 36 ).…”