NEW YORK • There are many ways to cope with exercising in hot weather. But one of the most effective may be, surprisingly, to soak in long, hot baths in the days beforehand, according to a new study of how best to prepare for athletic competitions in the heat.
When it is hot, our hearts labour to shunt more blood to the skin, which allows internal heat to dissipate but also leaves us feeling fatigued and potentially at risk of heat illnesses, ranging from nausea to heatstroke.
Scientists and coaches have come up with many ways to help athletes cope. Some involve a process known as precooling, which entails drinking icy beverages or applying ice to the skin before exercise, on the assumption that we can better withstand high temperatures outside by lowering our body's internal or skin temperature beforehand.
Other strategies emphasise heat acclimation, which is the slower process of adapting to high temperatures over the course of days or weeks: Your body changes in many ways, including starting to sweat earlier and more profusely, which helps to reduce the build-up of internal heat and ease the demands on your heart.
However, few studies have compared the benefits of acclimation and precooling, or have examined whether you gain extra benefits from combining both.
So for the new study, which was published in May in the Journal of Strength and Conditioning Research, scientists at the University of Brighton in England and other institutions invited nine recreational runners who were not heat-acclimated to their laboratory and set the temperature to 32 deg C.
The scientists asked the runners, who included one woman, to complete a simulated 5km race at top speed on a treadmill in the sweltering room. They had to repeat that race on three subsequent visits.
The reduction in time achieved by runners who followed set procedures in laboratory tests in England.
Before one of these, the runners precooled their skin by thrusting an arm into a vat of cold water and also donned cooling vests and athletic underwear fitted with ice packs.
After 20 minutes, they doffed their ice packs and ran again.
Then the scientists began formally acclimating them to the heat. They did this by dialling up the temperature to almost 37 deg C and having their volunteers pedal an exercise bicycle for about 90 minutes, at an increasingly vigorous pace - which they did for five consecutive days. Afterwards, the runners repeated their 5km treadmill race.
Finally, during a last visit, the runners, still heat acclimated, precooled as they had before with frozen undergarments and a chilly arm plunge and ran again.
The scientists then simply compared their times. As expected, the runners were slowest in their first run, when they had not prepared for the heat at all.
After precooling, however, they were significantly faster, improving by almost 4 per cent.
They were even speedier after four days of acclimation, reducing their time by more than 6.5 per cent compared with their first run.
Interestingly, they gained little more by combining acclimation and precooling. Their times in that final run were barely faster than after acclimation alone.
The upshot of these results is that "you will receive a bigger bang for your buck from acclimating to the heat rather than by temporarily cooling yourself down" with chilled clothing and such, said Carl James, who led the study while at the University of Brighton.
On the other hand, precooling can be a useful stopgap measure when temperatures suddenly rise and you do not have time to acclimate before a looming competition, he said. "Throw your ice vest and cooling shorts into the freezer" and wear them for about 20 minutes before your event, he advises.
Acclimation demands far more time and planning.
During your first workouts in summer heat, he says, reduce the time you spend outside and go at a gentler pace than normal, slowly ramping up your effort as the exertion begins to feel more tolerable. Drink plenty of water, too, he says, since you will start to sweat more profusely.
Or, alternatively, "lie in a hot bath, heated to at least 40 deg C, for 30 minutes after a 30-minute run," he said, which can amplify your body's adaptations to the heat without requiring more time outside in the high temperatures.
But James said even careful acclimation or precooling will not make you immune to heat illness.
"Headaches, nausea, dizziness and muscle cramping are all indicators of heat illness, at which point you should slow down and seek shade," he said.