Heat and Running
  Kurt Ellingson 12:00 AM
The longest event of my life, Western States 100, is a mere 49 days away. On a day where there are going to be many uncertainties, there is one thing I know for sure, it is going to be hot! Year after year, I read stories about how the heat in Squaw Valley (California) was the one factor that ruined someone's race. The heat affects so many different aspects of a persons performance- pace, hydration, ability to take in food (nausea), blisters, etc.

My boyfriend, who is also doing the race, has begun to heat train in a sauna. I have only been twice now. No, we don't run in the sauna, nor do we even jog on the spot, we simply sit there and count down the minutes until we can get out! Oh ya, and we drink A LOT of water!

I have been a little sceptical in regards to when exactly we needed to start acclimatizing to the heat. It seemed a little odd to be starting 3 months out of competition when from what I have learned in university, it only takes 14 days to acclimatize to factors such as heat and altitude. I came across an article on heat training and running and I thought I would share some of it with you here:

How Heat Affects Running Performance (by Bryon Powell,
There is little doubt that exercise performance is impaired in hot environments. While the effect of heat on performance varies with the sport (for example, less effect on cycling than running), there is a great deal of empirical data showing a link between ambient temperature and performance. Various authors have suggested performance impairments of between 1.6 and 3% in marathon times for every 10 degrees above 55 degrees Fahrenheit. Below is an interesting table from a paper by Scot Montain and colleagues at the US Army Research Institute of Environmental Medicine illustrates the relationship between elite marathoner finishing times and course temperature in the New York City Marathon.

times vs temp

New York City Marathon: Top Times vs Temperature (right)

How We Acclimate to Heat
If it is plasma that is the essential cooling component, is it possible to improve this problem by increasing our total plasma volume? Yes, and that is exactly what happens as we adapt to heat over time. Whether you acclimate naturally to higher temperatures over the course of a season, or in a heat chamber, the most significant change that occurs is an increase in plasma volume. Other things occur as well (such as changes in sweat sodium concentration, resting core temperature and heart rate), but plasma volume expansion is the key. After extensive acclimatization, plasma volume can have expanded by as much as 2 liters!

This may explain why the fittest athletes adapt to heat stress more quickly than the less fit. One of the by-products of endurance training (especially at high intensities) is an increase in plasma volume. So just by training hard, you can derive some amount of heat acclimation. What about specifically training in a hot environment to improve performance in a hot race? There is extensive evidence that it is possible to improve our performance in hot environments by training in similar conditions prior to competition. Several studies have demonstrated performance improvements in terms of maximum work rate, perceived exertion, time to failure at submaximal work rates, and time to complete a specific distance.

In the last few paragraphs we've explored a bit about the effect of heat on performance (bad) and the effects of acclimation on this (good). The most meaningful physiological adaptation that occurs is an increase in plasma volume (a lot like adding more radiator fluid to a car). However, there are some other adaptations that occur – changes in sweat rate, changes in sweat sodium concentration and changes in core resting temperature, to name a few. The various adaptations occur with different amounts of acclimatization. Here's a graphical representation of the times over which an athlete can gain these benefits:

A timeline of various heat acclimation adaptations (right).

Heat Acclimation Methods and Considerations
The work needed to achieve the benefits heat acclimation is reasonable. Most laboratory based heat acclimation protocols have athletes spend about 1 hour a day in a heat chamber for 7-10 days. Importantly, this needs to occur as close to the time of the competition as possible, as the adaptations conferred by acclimation decay rapidly without ongoing exposure. So there's no point in spending 2 weeks in a heat chamber a month before the race – the effects will decay in 1-3 weeks.

As previously mentioned, the benefits of heat acclimation decay rapidly if you do not maintain heat exposure. Estimates vary, but it's possible that you could lose half of the benefit in 10 days without ongoing heat exposure. This raises some logistical problems for athletes living in cold environments who are attempting to acclimate for a hot weather event. To benefit maximally from acclimatization, the heat training sessions should occur as close as possible to the event. That seems pretty straight forward. The problem is that acclimation is quite physically demanding, and most athletes attempt to taper in the week(s) prior to a big race. So, if you want to acclimatize optimally, it needs to occur during your taper – which may cause overtraining, or at least minimize the benefits of tapering.

As with all training, the more specific, the better. When it comes to heat acclimatization this means that your training climate should reflect the competition environment as closely as possible – the same temperatures as well as humidity. Why is humidity important? As anyone who has survived an East Coast summer knows, humidity makes it harder to lose heat via sweating. Training in a humid environment does confer some benefit it you are training for a dry, hot race, but not as much as training in a dry, hot chamber. Interestingly, there is better "transfer” of acclimation if you train in a dry, hot climate and then race in a humid, hot race than the other way round. So, as much as possible, match humidity and temperature of your acclimation phase to your race environment.

What about passive acclimation? That is, will sitting in a sauna at the YMCA get us ready for running in Death Valley? Essentially – a bit, but not much. Acclimatization is vastly greater (and more rapid) is you exercise during the heat exposure. Whether this is again the principle of specificity, or whether it is simply that core temperature rises faster with active acclimation (increased core temperature is probably the stimulus for the adaptations that occur) is not clear.

So, in my experience, heat acclimation based on well documented scientific principles can give athletes a significant performance enhancement in hot environments. However, it is important to recognize the effect of acclimation on the tapering period and to plan accordingly.

I was chatting with a friend last weekend as we were adventuring through the mountains in Squamish. She has run one of the hardest footraces on the planet, Badwater, where the temperatures reach somewhere in the 50's. To acclimatize, she heat trained the 2 weeks leading up to the event. She started with 10 minutes and worked her way up to 2 hours. She didn't move around in the sauna and she said by the end she was drinking 4L of water. She said the heat wasn't a problem for her during the race. In the end, if you are doing a race in a hot climate, it is best to prepare yourself accordingly and try and mimic that environment as best you can before getting to the start line.

Nicola Gildersleeve
Athlete Ambassador

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