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Wet-bulb globe temperature (WBGT) is widely used to simulate outdoor environments in indoor experiments. However, the effects of comparable WBGT conditions with and without solar heat load on thermoregulatory responses are unclear. This study investigated thermoregulatory responses in comparable WBGT environments with and without artificial solar heat load (Solar: 800 W∙m− 2 and No-Solar, respectively) and a condition with the same ambient temperature and relative humidity, but without solar heat (CON) during sedentary rest. Eleven healthy male participants were exposed to 28 °C WBGT under Solar and No-Solar conditions or 25 °C WBGT in CON. Thermoregulatory responses, including rectal temperature and mean skin temperature, forearm and chest sweat rate, and skin blood flow were measured during 60 min of seated rest. Solar exposure significantly increased rectal temperature compared with No-Solar exposure (0.10 ± 0.15 °C vs. 0.01 ± 0.15 °C, p ≤ 0.041), whereas CON had the lowest rectal temperature (− 0.09 ± 0.11 °C, p ≤ 0.041). Similar patterns were observed for mean skin temperature. Forearm and chest sweat rates were significantly higher in Solar than in No-Solar and CON (p ≤ 0.013), and body mass loss was greater in Solar (319 ± 149 g∙h− 1) than in No-Solar (197 ± 95 g∙h− 1) and CON (138 ± 68 g∙h− 1, p ≤ 0.002). These findings suggest that despite comparable WBGT conditions, solar heat exacerbates thermoregulatory strain and hydration demands. Effective solar mitigation strategies and adequate fluid intake are crucial to prevent dehydration and heat-related stress during outdoor activities.
Heat exposure during exercise is a physiological stressor that athletes perceive and that can influence subsequent behavior. This study examined the sequential relationships among perceived health factors, perceived heat-related symptoms (dizziness, headache, nausea, and malaise), and performance-related athletic behaviors during summer training in Japanese collegiate athletes. A paper-based survey conducted in 2015 at 11 Japanese universities yielded valid responses from 1322 male and 552 female athletes. The survey assessed perceived heat-related symptoms, perceived performance declines (strength, power, endurance, concentration, perceptual-cognitive skill, and motivation), athletic activity conditions (e.g., prolonged duration, insufficient rest or hydration, excessive heat or humidity, solar radiation, poor airflow, and clothing discomfort), and health-related factors (appetite loss, sleep deprivation, diarrhea, sickness, dehydration, fatigue, mental stress, and, in females, menstruation) during summer sports.). Structural equation modeling revealed that perceived heat and humidity, poor airflow, and clothing discomfort were associated with unfavorable activity conditions. These conditions were linked to worsening perceived health factors, including fatigue, illness, and mental stress, which were subsequently associated with perceived dehydration and appetite loss, indicative of body fluid imbalance. This imbalance was strongly associated with perceived heat-related symptoms (males: β=0.92, R2=0.85; females: β=0.77, R²=0.74) and perceived performance declines (males: β=0.42-0.53, R2=0.28-0.67; females: β=0.23-0.56, R²=0.38-0.40) (all p < 0.001). These findings suggest that impaired perceived health status is associated with both heat-related symptoms and declines in physical and cognitive performance during summer training. Monitoring athletes' perceived health status may support timely training adjustments in hot environments.
The purpose of this study was to investigate associations between lifestyle habits, health factors, athletic activity conditions, and exertional heat exhaustion (EHE)–related symptoms among male college athletes in Japan based on a self-completed questionnaire. The paper-based questionnaires were distributed to 11 universities in Japan, and 2006 respondents completed the survey. Data of personal characteristics (age, body mass), lifestyle habits (sleep duration, use of air-conditioner while sleeping, and practice duration), perceived health factors (loss of appetite, sleep deprivation, sickness, dehydration, accumulated fatigue, and mental stress), perceived athletic activity (insufficient rest breaks, high ambient temperature, excessive humidity, strong solar radiation, lack of ambient wind, and clothing discomfort), and EHE-related symptoms (dizziness, headaches, nausea, and malaise) were collected. The association between lifestyle habits, health factors, athletic activity conditions (explanatory variables), and EHE-related symptoms (objective variables) was analyzed using the partial-proportional odds model. “Perceived dehydration” (odds ratios [ORs] 1.70–2.31, p < 0.002),” “sickness” (ORs 1.35–1.76), p < 0.001), “perceived accumulated fatigue” (ORs 1.13–1.31, p ≤ 0.001), “perceived mental stress” (ORs 1.17–1.31, p < 0.019), “lack of ambient wind” (ORs 1.12–1.19, p < 0.022), “loss of appetite” (ORs 1.16–1.23, p < 0.037), and “sleep deprivation” (ORs 1.15–1.17, p < 0.025) were positively associated with EHE-related symptoms, whereas “using an air conditioner during sleeping” (ORs 0.91, p = 0.047) during summer seasons was negatively associated. These findings suggest that athletes should be allowed to postpone or downregulate exercise intensity and/or volume based on their perceptions of dehydration, sickness, accumulated fatigue, mental stress, loss of appetite, and/or sleep deprivation in the summer to prevent heat illness.
As previous studies have reported, Indra (Skt: Śakra; Pāli: Sakka), or lord of the gods in the Trāyastriṃśa heaven, visited the Buddha and listened to his teachings in the Sakkapañha-suttanta of the Dīgha-Nikāya (DN) No. 21, and its corresponding Chinese translations from Sanskrit Āgama sūtras.
