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Heat acclimatization: what does it take?

Conventional wisdom says that we adapt to deal with heat after a week or two of high temperatures. But a study in the current European Journal of Applied Physiology suggests that it doesn’t happen automatically. These days, we spend a lot of time in air-conditioned homes, offices, cars and even gyms — so we may no longer get the stimulus we need to adjust to exercising in heat.

To test this proposition, researchers at the University of Ottawa tested a group of 8 volunteers in mid May and early September. They measured core temperature, skin temperature, skin blood flow, sweat rate, heart rate, and a few other variables during a 90-minute bike session at 60% VO2max — and found no significant differences even after a long, hot summer. The key: their subjects reported spending an average of just 18 minutes a day doing “moderate” or “intense” physical activity outdoors over the summer.

In comparison, chamber-based heat acclimation protocols known to elicit physiological adaptations require a minimum of 1 h of exercise at 50% of VO2max for ten successive days in order to elicit a physiological acclimatization.

There’s no doubt that heat acclimatization effects are real — enhanced sweat rate and greater blood flow to the skin, resulting in lower core temperatures. But you have to get out there and sweat to make it happen.

  1. Brian
    June 3rd, 2011 at 22:26 | #1

    Interesting study. I know that if I hike the Grouse Grind on a particularly hot day my time drops quite a bit. In order to get heat acclimated for a triathlon in the Okanagan I was wondering how much I’d have to do to get ready. The biggest problem for me is that it rarely gets hot for ten straight days in Vancouver!

  2. Brian
    June 3rd, 2011 at 22:27 | #2

    Would exercising in extra clothing (what I would normally wear in the winter) suffice if the ambient temperature wasn’t high enough?

  3. AG
    June 4th, 2011 at 04:19 | #3

    I think it’s more in the mind. Didn’t you post another article that covered that? I’m in TX…and the first hot days of the year are horrible, but you get to a point in 2-3 weeks (if you do stuff outside…like workout, or just eat on one of many very popular restaurant/bar patios here) where <95°F feels cool in the shade (sun is sun). Sames goes for riding in the heat…all you need is just more fluids. The only exception sometimes is hitting a slow climb during humid weather…then you can feel yourself cooking a bit.

  4. alex
    June 7th, 2011 at 17:23 | #4

    @Brian: Yes, I would think that extra clothing would help (though I’ve never seen actual studies). Certainly lots of athletes have tried that sort of thing while preparing for hot-weather races. I wouldn’t go overboard, but erring on the side of forcing yourself to break a sweat could be useful.

    @AG: Yes, there’s definitely an element of acclimatization that’s in the head (the previous post you’re thinking of is probably this one: http://sweatscience.com/cycling-in-the-heat-knowing-the-temperature-slows-you-down/). However, there are also real, measurable physiological changes that take place once you’ve acclimatized to heat: e.g. your sweat rate will increase, the blood flow to the skin (which dissipates heat) will also increase.

  1. June 6th, 2011 at 19:03 | #1