The Australian Open revamped its heat policy seven years ago. How does it work?

The Australian Open is a yearly headline grabber for the on-court action, but sometimes the focus shifts to a force beyond players' control – the weather. Most often, match delays are due to extreme heat or rain.

But occasionally things are worse. In 2014, a four-day heatwave led to a record number of player retirements. A ball kid fainted, a player vomited, and water bottles melted. This led to discontent among athletes and spectators alike about the management of the heat and the transparency of when play would be stopped.

A decade later, the way the Grand Slam handles extreme heat looks different. This change has occurred under the leadership of Carolyn Broderick, who recently served as the medical director for the Australian team at the Paris Olympics. After years of working with professional athletes, she was appointed chief medical officer for Tennis Australia and the Australian Open in 2017.

Dr. Broderick says updating the heat policy was a major focus, so she co-developed a way to assess athletes’ risk of heatstroke in real time. As the world faces more extreme heat in the future, she says similar policies should be introduced across all sports. “All sports need to have good, science-based extreme heat policies,” she says, “We have to be ready for a warming world.”

Athletes can experience nausea, dizziness, vomiting and headaches under heat stress. The Australian Open is hot. There are at least a few days every year where the maximum temperature exceeds 30 degrees Celsius. But scientists who study how heat affects the body are more interested in other weather measurements. This is because humidity also plays a big role in how hot a person feels. The higher the humidity, the harder it is for the body to release heat through the evaporation of sweat. This led to sporting events, including the Australian Open in the past, using a metric called Wet Bulb Globe Temperature (WGBT) to measure the impact of heat on athletes. It is a weighted temperature value that takes into account dry heat but also incorporates humidity.

But Ollie Jay, a professor of heat and health at the University of Sydney who co-developed the Australian Open policy with Dr. Broderick, says this measurement doesn’t always capture the full picture. Professor Jay says it was established by the US military in the 1950s when training new recruits in the southern heartland, where it is often very humid. However, summers in Melbourne can also be dry, so this method isn’t always suitable for our climate, he says. Also, the AO uses estimated WGBT measurements taken by the Bureau of Meteorology at nearby sites, so Professor Jay says this doesn’t necessarily reflect the true conditions on the tennis court.

Instead, Professor Jay’s team designed a new method that not only directly measures environmental conditions but also tests and estimates how typical tennis players react, based on the data. Through research, he settled on four factors that contribute most to a person’s risk of overheating – air temperature, humidity, wind speed and radiation from the sun and surrounding objects. The goal was to measure all of these factors in real time at the side of the tennis court. These readings would then be fed into an algorithm that estimates how a tennis player is physiologically responding to particular climate conditions, based on the athlete’s internal heat production and the clothing they tend to wear. “So you need to integrate six parameters to accurately work out what the risk is,” he says.

(Court surface temperature is not included in the equation, because Professor Jay says it doesn’t have a significant impact on body temperature.) Because there weren’t enough ways to adequately measure these factors at the side of the court in 2018, Professor Jay’s team developed their own device, called an Environmental Management Unit, or EMU. These devices started as homemade contraptions and were later refined into a commercial product. They have been used by World Rugby, the Australian Olympic team and even music festivals like Beyond the Valley.

Once the measurements from these devices – located next to four main courts and one outside court – are fed into the tennis player algorithm, they are translated into a five-point scale displayed on a dashboard. Professor Jay says the system, known as the AO Heat Stress Scale, was inspired by the simplicity of New Zealand’s fire danger rating system, where an increase in the index indicates an increase in risk. When the index hits 3, Professor Jay says the climate conditions are placing moderate stress on the athlete’s body. At this point, players will start implementing cooling measures, like using ice towels. A 4 indicates worsening conditions, so male players will be allowed a 10-minute break after the third set, and female players will get a 10-minute break between the second and third sets. When the scale hits 5 – the highest point – play on outside courts will stop and the roofs on indoor courts will be closed after even games in each set. This has only happened about three times in the past seven years.

Professor Jay says the system facilitates the gradual implementation of measures to prevent heat build-up. “Theoretically, players can be exposed to hotter conditions for longer, while still remaining healthy and performing.” Dr. Broderick, the tournament’s chief health officer, says the system is not only easy to understand but also increases transparency. “Our policy is based on science, so it’s not at anyone’s whim,” she says. “[The index] is in every player-facing area, so we have it in the treatment rooms, we have it in the corridors where the players come, we have it in the recovery centre. I think it’s really important to engage [the athletes] so they don’t think it’s some sort of secret operation.”

The heat policy starts well before the tournament begins. Dr. Broderick says there is a strong emphasis on acclimatisation, especially for players coming from the cold northern hemisphere. “It’s been great to see a lot of them now coming out quite early,” she says. She also says education about reducing heat stress is important, such as encouraging players to take cold showers or ice baths before and after matches. Organisers have also improved conditions for spectators, including introducing more shade, misting fans and water fountains. But the policy is not static. Dr. Broderick says they are constantly improving it. Following the 2020 bushfires in Victoria, a PM2.5 monitor was added to the environmental monitors to measure the number of air pollution particles.

For this year’s tournament, Dr. Broderick says a predictive function has been added to the five-point scale. This means players can see the predicted heat index rating for their upcoming matches, “so it’s not completely out of the blue”. Dr. Broderick’s team is also working on scientifically determining if the policy has reduced heat-related illness at the tournament. She says they need to collect a few more years of data to showcase this research, but hopes that the lessons can be applied to other levels of sport and the general public. For example, some of the most effective methods athletes use to cool down, like ice towels, are easily implemented for most people. “I worry that as the world warms, it's not just going to have an impact on professional and elite sport, but also what it does to community sport and people's ability to be physically active,” she says. “Our other serious public health crisis is non-communicable disease from inactivity.”

But so far, Dr. Broderick says she thinks the policy is working well because it’s easy to understand and takes the “subjectivity” out of the equation. It all serves her larger ambition for humans and their health. Part of this work includes an online tool she co-developed with the Australian College of Sports and Exercise Physicians, where anyone can input their sport and location to calculate their heat risk on any given day. “We have to make it as safe as possible for people to stay physically active in a warming world,” she says.