Analysis of the outdoor training effects on fatigue performance and thermal comfort in summer

Climate change and rising global temperatures have raised concerns regarding outdoor activities and physical training. These issues require special attention in China, where physical training is common for university students. This study was conducted in Guangzhou, China, from September 2 to September 17, 2022, where students were trained for approximately two weeks, and 1180 valid questionnaires were collected to investigate the correlation between fatigue and training time by evaluating thermal sensations during physical training and analyzing changes in physiological parameters and fatigue levels throughout the training. The fatigue level and its correlates were discussed using Kaplan-Meier (KM) survival analysis and hazard analysis. The results revealed a substantial correlation and significant relationship between the mean thermal sensation vote and thermal index. Total fatigue scores were significantly correlated with the universal thermal climate index (UTCI), and fatigue levels were positively correlated with UTCI. According to the percentage distribution of each fatigue level with training time, more than 15 % of the subjects should rest after 11 a.m. Additionally, hot weather accelerated fatigue events. The increased caloric index exacerbated physical fatigue and symptomatic performance. Additionally, the proportion of negative emotions among students increased in hot environments, consequently, increasing mental fatigue. Fatigue was studied using KM survival and hazard analyses related to training time by incorporating several factors. UTCI, heart rate, tympanic temperature, and Tskin were found to produce a greater risk of fatigue events when they reached certain values. Based on the results, training time was recommended to be adjusted to 3.0 h and 2.5 h in the morning and afternoon, respectively. The results of this study will assist in adjusting student training time, reducing the occurrence of heat strokes in students during training, and maintaining overall student health.