Greater thermoregulatory strain in the morning than late afternoon during judo training in the heat of summer

Abstract

Purpose The time-of-day variations in environmental heat stress have been known to affect thermoregulatory responses and the risk of exertional heat-related illness during outdoor exercise in the heat. However, such effect and risk are still needed to be examined during indoor sports/exercises. The current study investigated the diurnal relationships between thermoregulatory strain and environmental heat stress during regular judo training in a judo training facility without air conditioning on a clear day in the heat of summer. Methods Eight male high school judokas completed two 2.5-h indoor judo training sessions. The sessions were commenced at 09:00 h (AM) and 16:00 h (PM) on separate days. Results During the sessions, indoor and outdoor heat stress progressively increased in AM but decreased in PM, and indoor heat stress was less in AM than PM (mean ambient temperature: AM 32.7±0.4°C; PM 34.4±1.0°C, P<0.01). Mean skin temperature was higher in AM than PM (P<0.05), despite greater dry and evaporative heat losses in AM than PM (P<0.001). Infrared tympanic temperature, heart rate and thermal sensation demonstrated a trial by time interaction (P<0.001) with no differences at any time point between trials, showing relatively higher responses in these variables in PM compared to AM during the early stages of training and in AM compared to PM during the later stages of training. There were no differences between trials in body mass loss and rating of perceived exertion. Conclusions This study indicates a greater thermoregulatory strain in the morning from 09:00 h than the late afternoon from 16:00 h during 2.5-h regular judo training in no air conditioning facility on a clear day in the heat of summer. This observation is associated with a progressive increase in indoor and outdoor heat stress in the morning, despite a less indoor heat stress in the morning than the afternoon.

Thermal strain is greater in the late afternoon than morning during exercise in the gym without airflow and air conditioning on a clear summer day

“…We investigated to what extent the time-of-day affects thermal strain during 2.5-h badminton training sessions in the gym without airflow and air conditioning in hot summer environmental conditions. Pre-exercise T sk , T ty and HR were lower in AM than PM trial (Figure 3) which is the common finding in chronobiological studies (2,3,(24)(25)(26). These time-of-day effects would provoke an interaction in T sk , T ty and HR which indicate greater increases in these variables during the sessions in AM than PM trial.…”

“…During 3-h baseball (1) and 2-h soccer (2) training sessions, there were higher mean skin temperature (T sk ), infrared tympanic temperature (T ty ) and heart rate (HR) in AM than PM trial when no time-of-day differences in ambient temperature (T a ) and wet-bulb globe temperature (WBGT) were existed. Moreover, during 2.5-h judo training sessions, there was high T sk in AM than PM trial when higher T a in PM than AM trial with no time-of-day difference in WBGT was observed (3). These studies therefore concluded a greater thermal strain in AM than PM trial because of an increase in environmental heat stress with increasing solar radiation during AM trial compared with a decrease in environmental heat stress with decreasing solar radiation during PM trial (1,2,3).…”

“…The greater thermal strain and risk of exertional heat-related illness have been reported in the morning from 0900 h (AM) than in the late afternoon from 1600 h (PM) in high school athletes during outdoor (1,2) and indoor (3) team training sessions in hot summer environmental conditions under a clear sky. During 3-h baseball (1) and 2-h soccer (2) training sessions, there were higher mean skin temperature (T sk ), infrared tympanic temperature (T ty ) and heart rate (HR) in AM than PM trial when no time-of-day differences in ambient temperature (T a ) and wet-bulb globe temperature (WBGT) were existed.…”

“…These studies therefore concluded a greater thermal strain in AM than PM trial because of an increase in environmental heat stress with increasing solar radiation during AM trial compared with a decrease in environmental heat stress with decreasing solar radiation during PM trial (1,2,3). However, since only one study (3) has investigated the time-of-day effect of indoor team training sessions on the risks of thermal strain during exercise, further investigation is warranted.…”

“…Therefore, the aim of the present study was to examine the time-of-day influence of the badminton training sessions in the gym without airflow and air conditioning on thermal strain in high school athletes in the summer heat. We hypothesised that the thermal strain would be greater in AM than PM trial owing to an increase in indoor environmental heat stress during AM trial, given the results of previous studies (1)(2)(3).…”