Limitations Exist In Reducing Exertional Heat Illness Risk Through Activity Modifications In Organized School Sports

Activity modification guidelines based on wet bulb globe temperature (WBGT) are widely utilized in sports; however, the association between the actual modifications implemented by teams and the incidence of exertional heat illness (EHI) is limited. PURPOSE: To investigate activity modifications implemented by organized school sports in Japan and their effectiveness in reducing the odds of EHI. METHODS: Participants submitted their daily activity log between June 1st and September 30th from 2019 to 2022. The log included (1) activity date, (2) participant number, (3) activity site (indoor, outdoor), (4) on-site WBGT, air temperature, and relative humidity at the start of activity, (5) on-site peak WBGT (if the data is available), and (6) multi-select activity modification list (activity cancellation, change activity start time, change activity location, increase rest breaks, increase hydration breaks, modify exercise intensity, shorten exercise duration, removal of equipment, and modify clothing ensemble). Incidence rate (IR) of EHI was calculated using 1,000 athlete-exposure (AE). Odds ratio (OR) and 95% confidence interval (CI) were calculated. Multiple-logistic regression was used to evaluate factors associated with EHI occurrence. Statistical significance was set at p<0.05 a priori. RESULTS: A total of 2,152 activity sessions were logged, with 58,106 AE. The overall IR of EHI was 1.98/1,000 AE (95%CI, 1.63―2.38), with a greater IR in outdoor than indoor (outdoor, 2.27/1,000 AE, 95%CI=1.86―2.76; indoor, 0.94/1,000 AE, 95%CI=0.48―1.64). The odds of EHI were 2.2 times greater when on-site WBGT at the start of activity was greater than 28°C (95%CI, 1.39― 3.65; p<0.001). When the threshold was increased to 31°C, the odds increased to 4.5 (95%CI, 2.40―8.58; p<0.001). The top three activity modifications were increased rest breaks, increased hydration breaks, and shortened exercise duration. The only factor that influenced the odds of EHI occurrence was the on-site peak WBGT, where a degree increase in WBGT raised the odds of EHI occurrence by 32.2% (χ2[11]=63.10,p<0.001; Nagelkerke R2=14.6%). CONCLUSIONS: Activity modification did not reduce the odds of EHI occurrence in the current data set. Continuous WBGT monitoring is recommended to identify its peak, which was associated with the risk of EHI. Supported by: This study was supported by Japan Society for the Promotion of Science KAKENHI Grant #19K19996.