This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Rising temperatures caused by climate change are making it harder to organize outdoor sports events safely. Exercising in the heat lowers performance and raises the risk of heatstroke, which is a leading cause of nontraumatic death among professional athletes.
In Japan, where school tennis championships are often held during summer vacation, excessively hot days pose a significant challenge for organizers. With many matches to complete within a fixed schedule, they face a difficult balancing act between protecting players from heat-related illnesses and ensuring that the competition can finish on time. One of the most widely used tools for assessing heat stress on a given day is the wet-bulb globe temperature (WBGT), an index that accounts for air temperature, humidity and solar radiation.
The International Olympic Committee and many sports federations rely on it to guide decisions about whether exercise should continue under hot conditions. However, WBGT can only indicate when conditions may be hazardous; it does not help organizers determine whether it will be possible to finish a tournament considering factors like long matches or unexpected disruptions. There is no well-established approach to convert such heat measurements into estimates of available playing time and scheduling margin.
To tackle this problem, a research team led by doctoral student Hiroki Yamaguchi from the Graduate School of Health and Sports Science at Doshisha University in Japan has developed a framework for evaluating whether tennis tournaments can be completed under high-heat conditions. Their study, published in the journal Frontiers in Sports and Active Living on Oct. 9, 2026, was co-authored by professor Kojiro Ishii of the Faculty of Health and Sports Science at Doshisha University. The researchers analyzed more than 119,000 hourly WBGT observations collected between 2018 and 2022 at 11 meteorological stations across Japan.
Following the heatstroke prevention guidelines of the Japan Sports Association, the team counted hours with a WBGT below 28 as "low-risk operational time." Then, they converted these hours into practical tournament indicators, such as feasible tournament days and the number of matches that could be completed. As a benchmark, the researchers modeled the first day of the individual tournament at the 2025 Inter-High School Athletic Meet, comprising 180 matches. Assuming 20 courts based on recent tournament practices and 30 minutes per match plus a 10-minute turnover, they set the required operating time at six hours per court per day.
The operational margin was calculated as the difference between the WBGT-based low-risk operating hours and the required operating time. Then, they compared tournament schedules across different periods from July to September, using three daily scheduling models. These were the standard 9 a.m. to sunset format, as well as an early-morning format and a nighttime format that both avoid the midday peak.
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