Tokyo Olympic Games: The science behind beating the heat

If the Olympic Games in Tokyo this year go ahead despite the threat of coronavirus, they're expected to be the hottest in living memory. Four years ago in Rio de Janeiro we saw stark images of French racewalker Yohann Diniz, who after leading the 50-kilometre event comfortably, began to experience severe gut problems, lost blood from his bowels, and collapsed multiple times in the heat.

Diniz refused to give up, and after three hours and 46 minutes, staggered over the line in eighth place. The temperature in Rio that day was around 28°C and 75 per cent relative humidity in the latter stages of the event. Conditions in Tokyo this year are expected to be even hotter.

Temperatures in Tokyo during July and August often exceed 30°C, with high humidity. The last summer Olympics in Tokyo, in 1964, were held in October. Already the marathon and race walk events for this year’s Tokyo Olympics have been moved 800km north to Sapporo.

Because of the expected harsh conditions, coaches, doctors and sports scientists working with Olympic athletes have spent the past two years preparing for this exact heat scenario.

Monash researchers have contributed to a comprehensive paper – the Sports Dietitians Australia (SDA) Position Statement: Nutrition for Exercise in Hot Environments. It was published in the International Journal of Sport Nutrition and Exercise Metabolism. The SDA’s announcement of the findings has also been released.

The paper brings together researchers and practitioners from sports medicine, thermal physiology, and sports dietetics, including Monash researchers Dr Alan McCubbin (the paper’s lead author), Dr Ricardo Costa and Ms Stephanie Gaskell from the Department of Nutrition, Dietetics and Food, and Dr Joanne Caldwell Odgers from the Department of Physiology. This follows a previous review paper in 2019 from Dr Costa, Ms Gaskell and Dr McCubbin looking specifically at the effect of heat on the gastrointestinal tract during exercise.

It's an effect on athlete health and performance that “should not be underestimated”, said Dr McCubbin.

“Whilst athletes in short, explosive events, like sprinters, actually perform better in hotter conditions, in the events lasting more than about 30 minutes, body temperature rises, and this starts to reduce athletic performance,” he said.

“However, there are several strategies that can help to minimise this effect, and give the well-prepared athlete an edge on their competition. This position statement brings together the most up-to-date summary of those strategies.”

Acclimation and acclimitisation

Athletes can prepare for hot weather through either heat acclimatisation (training in a hot location well ahead of competition), or heat acclimation (training in an artificially heated environment before the event.)

By raising body temperature for an hour or more a day, for up to two weeks, the body responds by increasing blood volume, lowering resting heart rate and core body temperature, increasing the amount of sweat produced at any given body temperature, and reducing the perceived level of effort during exercise.

Dr Caldwell Odgers wrote the sections of the paper dealing with acclimation.

“There’s not a lot you can do during an event as an athlete apart from hydrate,” she says.

Training repeatedly in the heat leads to "sweat hypertrophy", or an increase in the number of sweat glands.

“As your temperature increases you sweat and lose heat through evaporation of sweat, and so you maintain a lower temperature – that is the benefit. The components of sweat production change. You end up conserving more sodium [salt] which helps with hydration.”

“There’s not a lot you can do during an event as an athlete apart from hydrate.”

Dr Caldwell Odgers says "decay" sets in when acclimation training stops, but only by 2.5 per cent of the adaptations in heart rate and core temperature per day. This means it's possible for athletes to begin acclimation training before an event then pick it up again after travelling.

But the best preparation is reserved for those athletes in long-distance events who come from the place where the event is held. She cites the example of the 1984 Olympics in Los Angeles, where the first women’s marathon was run. The winner was a local outsider. The favourite, from Sweden, came 37th, and finished the race staggering and disorientated due to heat illness.

Watch: The unforgettable finish to the 1984 Los Angeles Women's Olympic marathon 

With all that sweating going on, hydration is unsurprisingly a big focus for athletes in the heat. There has been some controversy in hydration research over the past couple of decades, with some researchers advocating athletes should simply drink according to thirst, and others arguing this is inadequate for optimal performance.

Dr McCubbin, who also consults to Triathlon Australia’s high-performance program, says the new paper took a pragmatic approach.

“In the real world of elite sport, factors like fluid availability, opportunities to actually drink it, and gut tolerance of those fluids, will often dictate how much an athlete drinks.

“The argument about how much of their sweat losses should be replaced is fairly academic for most events seen at the Olympic Games.

“It’s been estimated that elite marathon runners spend less than one minute of the race with a drink bottle to their mouth, and swallowing fluid and breathing whilst running 21kmh is not an easy task.”

Icy strategies

Other nutrition strategies can also help athletes, including those that lower core body temperature prior to exercise (pre-cooling). Ice slushies were first used by Olympic athletes before the marathon at the Beijing Olympics in 2008, and are likely to be used again in Tokyo. Towels dunked in ice water are also draped over their bodies, to provide a greater buffer for increasing core temperature before performance is negatively affected.

Ms Gaskell supported one Australian marathon runner, Julian Spence, at last year’s world championships in Doha, where conditions were similar to that expected in Tokyo.

“It was interesting to see in Doha only about four countries pre-cooling,” wrote Spence on a blog. “I watched one African team run for 15 minutes beforehand in full tracksuits. They weren’t the ones that did very well!”

Another strategy is to alter the perception of body temperature, rather than lowering the temperature itself. Menthol (as a gel on the skin, or an ingredient in food and drinks) has been used in research to show a reduced perception of heat in athletes, and in some cases improved performance. Menthol can also be added to the ice slushies for an additive effect.

The position statement also highlights the unique needs of Paralympic athletes. Because sweating is controlled by the nervous system, athletes with spinal cord injuries don't sweat below the level of their injury, reducing their ability to thermoregulate. Spraying or pouring water over the skin, where practical, can assist in promoting evaporation by substituting for sweat, while pre- and per-cooling strategies can be of even greater significance to these athletes.

The paper’s authors feature on a podcast - (Nutrition for Exercise in Hot Environments) discussing heat and nutrition and running.