Measurement of steady state and dynamic metabolic rates under typical daily activities

Abstract

An increasing number of studies have focused on the impact of metabolic rate (M), an essential factor affecting thermal regulation in the human body, on thermal comfort. However, current standards and research have several limitations. First, the quantitative relationship between M and time was not addressed after changes in the activity status. Second, walking M varied significantly among the different standards. Third, the applicability of the empirical equation for calculating M using heart rate in ISO 8996 is controversial. To address these problems, five experiments were conducted to measure M using indirect calorimetry with a cumulative total of 78 male subjects. These activities primarily involved sitting, standing, and walking at 2–5 km/h. The initial four experiments were conducted at 26 °C, and the fifth was conducted at 30 °C. The results showed that the M demonstrated a first-order exponential decay with time after a change in activity status, within the M range of 1–3.8 met. The steady-state M corresponding to typical daily activities was obtained, and the reasons for the differences between the measured M and the recommended values in the standards were analysed. The empirical equation approximating M with heart rate can estimate M with a deviation of 20%–30% when the heart rate is 10–14 bpm higher than the sitting heart rate. These findings provide a theoretical foundation for evaluating thermal comfort across different activity intensities in both indoor and outdoor environments.