Abstracts

Background: In indoor environments such as gymnasiums, the effect of exposure to solar radiation is less severe, however, heat is more likely to accumulate, and humidity is higher than in outdoor environments. Therefore, the efficiency of heat dissipation by living organisms becomes less efficient, and the environment may be prone to dehydration due to increased sweating. The actual duration of the main events in physical education (P.E.) classes varies across schools. More than 30 minutes of exercise in a hot environment is considered to present sufficient thermal stress for students. In some cases, students cannot consume water due to the time constraints of the class. There are only a few experimental studies on the prevention of dehydration in P.E. classes in Japan. Therefore, it is important to examine the effects of water intake on organisms during P.E. classes.

Objective: This study aimed to examine the effects of water shortage on various physiological responses and subjective symptoms during summer P.E. class.

Methods: Twelve healthy young males (age: 20.3 ± 0.5 years) volunteered to this investigation and play the practice of basketball for 50 minutes under the simulation high school P.E. class in July (temperature: 30.3 ± 0.2 °C). They were divided into two conditions: one in which they could hydrate freely during the class (WI group, n=6) and another in which they could not be allowed to hydrate (NI group, n=6). Measurements included pulse rate, rating of perceived exertion (RPE), the subjective thirst (ST), body weight, dehydration rate, water intake, urine volume (UV), and urine specific gravity (USG). Those measurements were estimated before the class and after the main exercise and end of the class.

Results: Pulse rate, RPE, USG at the end of class and dehydration rate in the NI group were significantly higher than those in the WI group. There was a significant difference in dehydration rate between groups (WI vs. NI: 0.4 ± 0.5 % vs. 2.1 ± 1.3 %, p<0.05). Although the USG of the WI group after class was significantly lower than that of before class (p<0.05), there was no significant difference within the NI group. In the NI group, significant positive correlations were found between ST and pulse rate (r=0.703, p<0.05) and between ST and RPE (r=0.619, p<0.05). In the WI group, there was no significant correlation among changes in weight, USG, ST, or exercise load index (pulse rate, RPE).

Conclusions: Students who did not drink water during a 50-minute P.E. class indoors at summer temperatures around 30 °C were clearly more dehydrated than those who could drink freely.