Study of outdoor exercise in high temperature environments and recovery time recommendations based on physiological...

Global temperatures are gradually increasing, and people are facing the risk of thermal injury when exercising in hot outdoor environments, and are especially susceptible to heatstroke when working in high temperature outdoor environments. Currently, most of the existing studies focus on the changes of human physiological parameters during exercise in hot environments, and there are limited studies on post-exercise recovery, and most of the studies on physiological parameters during the post-exercise recovery period have been conducted in indoor environments. In this study, Participants performed different exercise intensities in a hot outdoor environment characterized by a Wet Bulb Globe Temperature (WBGT) of 31 ± 0.28 ℃-a comprehensive thermal stress index that integrates ambient temperature, relative humidity, wind speed, and solar radiation to quantify heat-related physiological impact on humans. Participants moved at 5 km h⁻¹, 7 km h⁻¹, and 8 km h⁻¹ for moderate, high, and very high exercise. The experiment collected objective physiological parameters (heart rate, core temperature) continuously during the 20-minute pre-exercise rest period, throughout exercise, and 50-minute post-exercise recovery, as well as subjective thermal responses, which were assessed only before exercise initiation and immediately after exercise cessation. Additionally, the Physiological Strain Index (PSI) - a comprehensive metric integrating core temperature and heart rate to quantify human thermal strain on a 0-10 scale - was used to define post-exercise recovery completion (with PSI ≤ 2 as the recovery criterion). The results showed that the recovery time of moderate exercise was smaller than 5 min. In contrast, high-intensity and above exercises necessitate longer recovery periods. There was a strong correlation between core temperature at the conclusion of such exercises and the required recovery time. Based on this relationship, a predictive equation for recovery time was developed using core temperature at the end of exercise, achieving an R² value of 0.83. The results of this paper can provide recommendations for the length of recovery time for operators in high temperature environments, thus protecting the safety of operators.