The average summertime high in Qatar, which is slated to host the 2022 World Cup, is above 40 degrees Celsius. That made it a fitting location for a recent gathering of physiologists and sports medicine experts to formulate updated guidelines for training and competing in hot conditions, which were published in this month's issue of Sports Medicine and two other journals.
While the basic advice remains unchanged – take time to adjust to hot weather, moderate your effort, drink plenty – the details continue to evolve. Here are five topics where new research is changing how athletes handle heat.
Who's at risk
New research from Matthew Cramer and Dr. Ollie Jay of the University of Ottawa's Thermal Ergonomics Lab challenges two enduring myths about who gets hottest. The first is that, as an article in The New York Times claimed last week, "body fat is the ultimate heat insulator."
It's true that obese people tend to sweat more, notes Jay, who is now at the University of Sydney, "but this is not an independent influence of body fat, it is the extra heat they have to produce to carry that weight." In other words, bigger people get hotter whether they're hauling around muscle or fat.
The second myth is that fitter people develop the ability to sweat sooner and more copiously, as a way of shedding heat. In fact, Jay says, if two people of the same size run at the same speed, they'll generally sweat similar amounts. Fit people only seem to sweat more because they're able to run faster or sustain higher work rates.
How to acclimatize
The single most important step you can take to enhance your performance in the heat is to acclimatize – that is, to exercise repeatedly in hot conditions until your body adapts by expanding the volume of blood plasma in your veins, increasing your sweating response and other adjustments.
The most rapid changes take place in the first week of acclimatization, with further adaptations during the second week. The most effective way to trigger changes is to exercise in hot conditions for an hour a day.
Need a shortcut? A recent study of British ultramarathoners found significant plasma boosts after just two two-hour runs in 30-degree heat, with a full day of rest in between. But a longer adjustment period is better – and easier.
How to acclimate
The weather outside doesn't always co-operate, so another option is to adjust to indoor heat instead, a process referred to as "acclimation" instead of "acclimatization." Doing a workout in a warm room with no fan is one approach; wear extra clothing if necessary to simulate the feeling (and copious sweating) of above-30-degree outdoor heat.
A more unconventional option that sports scientists have begun experimenting with is saunas. An Australian study published earlier this year in the European Journal of Applied Physiology found that cyclists who took a daily 30-minute sauna at 87 degrees after workouts experienced a boost in plasma levels after just four sessions. Researchers haven't tested whether hot yoga sessions can produce similar adaptations, but the possibility is intriguing.
Hydrate (and rehydrate)
How much to drink during exercise remains controversial, with some experts now saying that it's sufficient to simply drink when you're thirsty. If you're comfortable with that approach, then it's all the more important to make sure you replace lost fluids between workouts.
The problem, according to University of North Alabama physiologist Dr. Eric O'Neal, is that most of us are very bad at estimating how much fluid we lose during a workout. You can look out for warning signs such as darker-than-normal urine – or even, he suggests, take periodic measurements of your urine's "specific gravity" for better accuracy.
At the very least, be aware that you need to drink between workouts. O'Neal suggests fully replacing your sweat losses, which you can estimate by weighing yourself before and after a workout within 12 hours, and drinking the same amount again within 24 hours.
At the Beijing Olympics in 2008, Australian athletes downed crushed-ice drinks – slushies – to lower their core temperature before competing. This approach, along with similar tactics such as wearing ice-filled vests or old-school damp towels, can boost endurance in the heat.
But beware: a recent study by Jay and his colleagues, presented at the American College of Sports Medicine conference in May, found that the body responds to cold slushies by reducing your sweat rate. The response is so strong that you actually end up storing more heat over all.
That means the slushie approach may be best suited to very hot and humid conditions, where you're overheating so much that sweat is dripping to the ground instead of evaporating. Under those conditions, it doesn't matter if the slushie reduces your sweat rate, because sweat only cools you if it evaporates.