Climate change is already affecting the way we exercise. What does the future hold?

When the world’s first “modern” marathon was held in Boston in 1897, 15 men stood at the starting line. Fast-forward 127 years, and there were 30,000 participants (43 per cent of whom were female) at the 2024 Boston Marathon in April.

New research suggests more people than ever are signing up for marathons around the world. But this is happening against a backdrop of rising temperatures and an increasing number of events being cancelled due to extreme weather.

Changing climate is affecting the way we move.Credit: iStock

Last year was the hottest year on record, and the heat – along with wild weather events – is set to continue, with Australia especially susceptible to severe and extended bouts of extreme heat.

A new paper published in the MJA examined the impact of climate change on our health. Among its findings was that Australians are spending an increasing amount of time exercising in temperatures that exceed moderate, high and extreme heat stress threshold risks.

“In the last five years, the number of days that have exceeded each of these thresholds has increased quite substantially,” says one of the paper’s authors, Professor Ollie Jay, director of the Heat and Health Research Incubator at the University of Sydney. “This serves as an indicator of how climate change is already affecting us. And the concern is that, in the future, those trends are going to continue or, if anything, accelerate.”

The changing weather has implications not just for our planet and our health but also for the way we move and for our leisure and sporting activities.

“The impact, if we don’t change our behaviour, could be bad,” says Jamie Crain, chief executive of Sports Medicine Australia.

He is referring to increases in hospitalisations and deaths resulting from heatstroke, where the body’s ability to cool itself down fails. One study of 140,000 participants in endurance sports found they were 10 times more likely to suffer a life-threatening event or death from heat stroke than from a cardiac event.

But Crain is also referring to how extreme conditions affect our enjoyment of activity, especially given sedentary behaviour is already a health issue for Australians.

Will the weather become another reason why kids won’t be physically active outside, or will we all be less physically active in our everyday lives, avoiding play or active commuting because of heat-related physical discomfort?

“Those are the kinds of things I’m concerned about,” says Jay. “Below heat exhaustion [when we lose too much water and salt] and heatstroke, you’ve got suffering. We shouldn’t just pay attention when people end up in the emergency room.”

Crain imagines there will be a “natural evolution” in how we adapt to changing weather, including innovations to make clothing lighter and more breathable.

The way we physiologically cool ourselves is through the evaporation of sweat. If the sweat can’t evaporate because it’s too humid or because of the gear we are wearing blocks the body’s ability to do so, we will end up dehydrated but won’t cool down.

Apart from addressing gear, other feasible changes could be a move to playing certain sports indoors, earlier in the morning or later at night. There may be a different mix of sports being played in the next five to 10 years as people “self-select” away from activities that require them to spend hours under an unforgiving sun, and we may see changes in the time of year or the way organisers run events.

Some organisers have already made changes as they attempt to avoid cancellations and criticisms, like those levelled at the Australian “Sauna” Championships 10 years ago.

“At the Australian Open, it’s not the heat, it’s the stupidity,” frothed the New York Times as it described how, over four days with temperatures reaching 40 degrees, tennis players hallucinated, fainted, vomited, and experienced melted sneakers and water bottles.

Jay has worked with Tennis Australia for the past six years to prevent a repeat of this. Now, they work on a five-point sliding scale of risk and, as conditions pass various thresholds, ensure increased hydration, implement cooling strategies, add extra breaks and, finally, suspend play.

“People always ask: what do you do, and how hot is too hot? The answer is: it depends,” he says.

It depends on the temperature, humidity, solar radiation and wind. It depends on the intensity of the sport and our gear. It depends on the duration, how fit, healthy, and old we are, as well as our individual thresholds. What works for tennis will not be the same for a marathon, and understanding what is and is not effective is important.

Applying ice to our wrists might make us feel cooler, but it does not affect the heat in our bodies or reduce our risk of overheating. And, as important as hydrating is (the water temperature doesn’t matter), we can drink all the water in the world and still overheat. On the other hand, applying water to our skin where it evaporates without depleting the body’s water is really effective, Jay says.

Together with Sports Medicine Australia, he has created a new tool that provides evidence-based advice on how to exercise safely in the heat.

In more extreme conditions, it typically involves providing more shade, having more rest breaks and ensuring there is enough hydration.

Hugh Singe, the managing director of Event Health Management and medical director of the Sydney marathon, is hopeful.

“The overall population health gains, through participation in exercise and sporting events, far outweigh the risks of a particular activity,” says Singe.

“The risks associated with particular activities, such as marathon participation, can be largely and adequately mitigated through better-informed preparation.”

If heat stress is managed along the way, the thresholds for cancelling an event are likely to become higher.

“In the next five to 10 years, we’re going to have to keep on adapting,” says Jay. “We need to take the threat seriously, understand the risk, and be ready for it.”

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