Understanding the heat environment of tennis courts

With rising global temperatures due to global warming, the risk of heat stroke has increased and is expected to increase further. This is especially troubling for athletes who participate in competitive sports. In tennis, several matches are played every day, lasting a maximum of five hours. Playing such matches in sweltering conditions can be very damaging.

The 2021 Tokyo Olympics experienced extremely hot conditions, with many players calling for appropriate countermeasures. Consequently, at the Tokyo Olympics, the International Tennis Federation (ITF) formulated and issued the “Extreme Weather Policy” to manage matches based on temperature. Despite this policy, heat-related illnesses remain a major problem in tennis.

Tennis matches are played on different surfaces. In Japan, three types of surfaces are used: hard, sand-filled artificial grass and clay courts.

Studies have shown that the overall heat load on players can vary depending on the surface material, creating different microclimatic environments, unlike established weather stations.

Wet bulb temperature (WGBT), an index for measuring thermal environments, correlates strongly with heatstroke and is used for environmental assessment at sporting events.

Although several studies have been conducted to analyze the differences in WGBT between different tennis court surfaces, they have their limitations. For example, one study only took measurements in the afternoon, and another study failed to compare WBGT values ​​with those at the nearest station.

To address these issues, a team of researchers from Japan, led by Ph.D. student Hiroki Yamaguchi from the Graduate School of Health and Sports Science at Doshisha University, together with Professor Kojiro Ishi from the Faculty of Health and Sports Science at Doshisha University, investigated the heat environment of several tennis courts using WBGT meters.

Their findings have been published in Scientific reports on July 5, 2024.

“Exertional heat stroke is the second most common cause of non-traumatic death in competitive athletes. As a tennis player, I have also personally experienced heat stroke during competitions. Research into heat conditions on different tennis courts can serve as a reference for training guidelines and playing time and can contribute to effective heat management in the sport,” explains Yamaguchi, reflecting on his motivation for the research.

The team installed WGBT meters on an outdoor hard court, a sand-filled artificial turf field and a clay court. The measurements were taken hourly from 9:00 AM to 5:00 PM on weekdays from June 1 to September 21, 2022.

The Japan Tennis Association, in its guidelines for preventing heat stroke in practice, requires that the WGBT at the nearest weather station to the tournament venue be checked every hour when on-site measurements are not available. Therefore, the researchers compared their on-site WGBT values ​​with those of the nearest Japan Meteorological Agency station (JMA WBGT), based on the target levels.

The results revealed significant differences between the JMA WBGT and the on-site WBGT values. The average on-site WGBT values ​​for hard courts were significantly higher at the “Warning” level (ranging from 25 °C to 28 °C) and higher, for sand-filled artificial grass pitches at the “Serious Warning” level (ranging from 28 °C to 31°C) and above, and for clay courts at the “Danger” level (above 31°C), than JMA WGBT.

Hard and sand-filled artificial grass fields in particular are played in particularly warm conditions. The researchers emphasize the importance of determining the heat environment through on-site WBGT measurements on surfaces and taking proactive heat countermeasures using heat safety guidelines.

In addition, they urge organizers to reduce the frequency of afternoon matches and explore the possibility of holding matches in the early morning, evening and night.

“The results of this study highlight the importance of on-site WBGT measurements, as well as considering the surface and time of the match, to protect players, coaches, referees and spectators from heatstroke,” said Mr Yamaguchi .

He adds: “As WGBT only measures heat risk to the environment, the use of body heat balance models such as Predicted Heat Strain (PHS), aimed at quantitative measurement of heat risk, is required for developing more effective heat safety guidelines in the future. .”