Dave Elger

Over the years I’ve completed some hot weather marathons. How could I ever forget running 26.2 miles in Bali or Singapore, always wishing I’d done more hot weather training.

The effect of heat on endurance performance is a well-studied subject. It appears that the ideal temperature for activities such as distance running is 50-55 degrees, with performance decreasing by 2% for every 5-degree increase in temperature. And don’t forget the added stress of humidity, lack of air movement, and radiation. Fortunately, most, but not all, hot weather races start early so at least sun radiation can be avoided.

According to Physiology of Sport and Exercise by Wilmore and Costill, it takes more than mere exposure to a hot environment for the body to acclimatize. In order to enhance the body’s cooling mechanism during activity, you have to get out and exercise in the heat. Just sitting in a sauna or steam room won’t cut it! The environmental conditions plus the duration and intensity of exercise all contribute to the acclimatization process.

While cardiovascular changes occur in the first 3-5 days of warm weather training, it takes slightly longer, up to 10 days, for the sweating mechanism to adapt. A fully acclimatized athlete has a more efficient distribution of blood flow and a larger stroke volume (the amount of blood pumped per beat). Sweat is produced earlier to promote cooling and is more dilute conserving electrolytes. The capacity to sweat nearly doubles. It’s interesting to note that, according to Wilmore and Costill, even though total sweat produced during warm-weather exercise may not change with acclimatization, the amount produced in the most exposed areas of the body increases. Once fully acclimatized, athletes are able to perform more work and keep their body temperature and heart rate lower with a reduced risk of dehydration and overheating.

Any acclimatization achieved in 10-14 days can be reversed just as quickly when you don’t exercise repeatedly in the same oppressive conditions. Remember this next time you visit a cool climate for a few weeks and then wonder why exercise seems so difficult when you return to Okinawa.

I have noticed most Okinawan runners and walkers always seem to be overdressed for the conditions, allowing them to maintain a high level of acclimatization year round. If you have ever entered an Okinawan race, then you are fully aware that regardless of weather or time of year, the earliest start time (even full 26.2-mile marathons) is 9 am.

When the hot weather hits, the best advice is to slow down, cut back your distance, and increase your intake of fluids. Don’t expect to perform as well as you did throughout the winter months.

It’s a good idea to start the acclimatization process early by dressing a little warmer for your workouts before the hot weather really hits. They will be here before you know it!

(C) 2006 Dave Elger all rights reserved. http://www.daveelger.com
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Dave Elger is a well respected authority within the running community having written hundreds of articles on the topics of running and wellness. If you would like to contact Dave you may do so here on this site by leaving a comment, or by sending him an email at dave{@t]daveelger.com.  He also supports the Okinawa Running club at http://www.okinawarunning.com
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