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 non-traumatic 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 PhD student Hiroki Yamaguchi from the Graduate School of Health and Sports Science at Doshisha University, Japan, has developed a framework for evaluating whether tennis tournaments can be completed under high-heat conditions. Their study, published in Volume 8 of the journal Frontiers in Sports and Active Living on October 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, the required operating time was set at 6 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.
Their statistical analysis showed that adjusting playing hours had a stronger effect on the availability of low-risk hours than changing tournament dates. Both the nighttime and early morning models increased the odds of WBGT remaining below 28 by 46% and 36%, respectively. Notably, applying changes to both tournament dates and playing hours produced the greatest overall improvement, adding the equivalent of up to 0.8 days of low-risk playing time over a 7-day tournament period.
The researchers also investigated whether the analyzed schedules provided enough time to complete the benchmark tournament. While many scheduling scenarios met this requirement on average, the amount of extra time available varied considerably. For example, the July 11–20 early morning scenario had the largest average margin at 2.2 hours per day, while the September 1–10 standard schedule fell short of the requirement by an average of 0.5 hours per day.
These results suggest that passing a threshold is not enough and that organizers should carefully consider how much spare time remains under a given schedule . “Our approach provides decision makers with information directly relevant to tournament planning, rather than relying solely on environmental heat indices,” says Yamaguchi. The proposed method provides new indicators to complement existing safety guidelines by showing how much time is available before an event begins.
Overall, this novel framework provides a foundation for future discussions on climate-adaptive tournament scheduling and management. Organizers could use the proposed metrics to evaluate options to make large sporting events safer. “We believe that using operational margins and matching surplus to fundamentally review tournament dates, time of day, locations, the number of courts, and match formats will help protect players’ lives and support the sustainable hosting of tennis tournaments,” concludes Yamaguchi.
About Hiroki Yamaguchi from Doshisha University, Japan
Hiroki Yamaguchi is currently a PhD student at the Graduate School of Health and Sports Science, Doshisha University. His broader research interests encompass sports science, exercise physiology, heat exhaustion, and environmental physiology. He has extensive experience as a player, coach, and tournament organizer in tennis.
About Professor Kojiro Ishii from Doshisha University, Japan
Dr. Kojiro Ishii is a Professor in the Faculty of Health and Sports Science at Doshisha University. He obtained his Ph.D. in Physical Activity and Human Performance from Osaka City University in 1993. His research centers on the promotion of health and human performance through physical activity, nutrition, and environmental design, seeking solutions to specific practical problems. To date, Dr. Ishii has authored over 160 peer-reviewed publications.
Funding information
The author(s) declared that financial support was not received for this work and/or its publication.
Media contact:
Organization for Research Innovation
Doshisha University
Kyotanabe, Kyoto 610-0394, JAPAN
E-mail: jt-ura@mail.doshisha.ac.jp
Frontiers in Sports and Active Living
Observational study
Not applicable
Operational margin of high-school tennis tournaments under heat constraints: a wet-bulb globe temperature-based scenario analysis
9-Oct-2026
The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.