Comparison of thermoregulatory responses of elementary school children and junior high school students during baseball practice in summer

Introduction

The mortality rate of heat disorder among Japanese students during school sports activities is the highest during baseball practice. In this study, we investigated the thermoregulatory responses during baseball practice in elementary schoolchildren and junior high school students in summer.

Methods

The subjects were 29 elementary schoolchildren (ES:age11.3±1.3yr) and 19 junior high school students (JS:age13.7±0.8yr) belonging to a baseball sports boys’ team. As measurements, environmental temperatures (DBT, GT, WBT and WBGT), total sweat rate per unit area of body surface per hour (TSR:g/m2/h), the percentage of total sweat loss to initial body weight (%TSL), the percentage of fluid intake volume to total sweat loss (%FIV), tympanic temperature (Tty) and heart rate response (HR) were measured in baseball practice.

Results

There were no significant differences in various environmental temperatures between the two groups at any practice. WBGT in practice period ranged from 23C to 27C. The TSR and %TSL between the two groups was not significantly difference. The FIV (g/m2/h) and %FIV (%) of ES was significantly (p<0.001) higher than those of JS. The %DHR of JS was significantly (p<0.0001) higher than that in schoolchildren ES. The FIV was less than TSL, and %FIV was extremely low in two groups. The %DHR was correlated with FIV, %FIV, fluid intake per drinking, and frequency of drinking (p<0.001). The Tty after practice in ES was significantly higher (p<0.05) than that in JS.

Discussion/Conclusions

It has been reported that dehydration is less likely to occur in children than adults when fluid intake is not restricted [1], but our results differed from those [1]. Therefore, to prevent heat disorder s during sports activities in children, only encouraging them to drink liquids periodically is insufficient, and they should be instructed to aggressively increase the frequency of fluid break, shorten the practice time, and reduce exercise intensity in accordance with WBGT.

References

[1] Inoue, Y., et al. (2002). Age-related differences in sweat loss and fluid intake during sports activity in summer. Jpn. J. Phys. Fitness Sports Med.,51,235-244.