How to work out during a heat wave

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- Alex Hutchinson (@sweatscience)

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This week’s Jockology column in the Globe and Mail deals with exercising in the heat, covering topics like acclimatization, pre-cooling and (when needed) post-cooling. Actually, the version available online is only about half the article — not sure whether the rest will be posted later. In case it isn’t, here’s a sidebar that ran with the article (I hope!):

Beating the heat

1) Acclimatize: Research shows you significantly improve your heat tolerance after 10 to 14 days of exposure. But it’s not enough to just sit on the porch fanning yourself – you have to actually sweat. In a study published last year, researchers from San Diego State University had eight volunteers exercise for 10 days, 90 minutes a day after having Botox injected into one arm to block sweating. At the end of the study, the sweat glands in the sweaty arm were producing 18 percent more sweat – a sign of good acclimation – while the glands from the arm that remained dry became less productive.

2) Slushies: Olympic athletes have long been using fancy ice vests and cold baths prior to competing in the heat. In 2008, the Australian team unveiled a new, more convenient “pre-cooling” technique: slushies. They brought seven slushie machines to Beijing, using them for soccer, track, cycling, triathlon and a host of other sports. The secret formula: they diluted a standard sports drink by half with water, cooled it to -1° C, and drank 14 millilitres per kilogram of bodyweight shortly before competing.

3) Breathable clothing: A forthcoming study in the journal Applied Ergonomics put the claims of athletic apparel makers to the test, with volunteers exercising for an hour wearing either a cotton T-shirt or a polyester/elastane blend. As expected, the polyester shirt permitted greater sweating efficiency, and the sweat-soaked cotton shirt weighed 50 per cent more. Interestingly, though, the cotton shirt didn’t actually make the subjects any hotter – so if you’re committed to your retro gear, you can stick with it.

4) Dunk yourself: If you do find yourself overheating, the quickest way to cool down is to plunge into the pool – and you don’t necessarily need to subject yourself to an ice bath to cool down quickly. Some researchers now argue that pleasant water temperatures of 24-26° C are just as effective as colder temperatures, and can bring heat stroke victims back to safe temperatures in less than three minutes. The key: the warmer water doesn’t constrict the blood vessels under your skin, allowing more efficient heat transfer.

Plus an explanation of “wet bulb globe temperature”:

Wet bulb globe temperature (WBGT)
Developed for the U.S. Marines in the 1950s, the WBGT scale accounts for temperature, humidity, solar radiation and wind. The commonly reported humidex, in contrast, only accounts for temperature and humidity. Proper measurement of WBGT requires three separate thermometers, including one inside a black globe and another covered with a wet cotton wick. As a rough estimate, WBGT is higher than air temperature when the relative humidity is above 50 per cent, and lower when it’s below 50 per cent. The key difference from the humidex: direct sunlight raises WBGT compared to a cloudy day, even if the temperature is the same.