Sunday, June 18, 2006

Heat Exhaustion and Acclimation

As I sit here by the open window upstairs in our residence, I'm pondering the topics of heat exhaustion and heat acclimation. We just returned from dropping off our daughter and her boyfriend at the T (they were visiting for Father's Day and are now returning to Brooklyn), and the thermometer in the car registered 100 degrees in Harvard Square.

Dang. It really is hot now.

And I'm thinking about my dismal race last weekend where the humidity just did me in in the first half of the marathon, even though the temperatures were not that high. Obviously I was not acclimated to the race conditions. I started training for the marathon in the middle of the winter here. In fact, the first weekend of my training, when we visited NYC, included the biggest blizzard Central Park had ever seen. My cap froze to my hair on long runs along the Charles River. Looking over my running log, I had perhaps two runs where the temperature exceeded 70 degrees. I don't recall them being too humid. By mile 18 or 19 of the marathon, I was suffering from heat exhaustion. I wisely backed off to a slow (dead man walking) walk to the finish.

The symptoms of heat exhaustion may include increased heart rate, headache, dizziness, nausea, vomiting, clammy skin, quickened breathing. For me it was the nausea and vomiting, as well as clammy skin (as my body became unable to regulate its temperature through sweating). It wasn't "full-blown" heat exhaustion, but likely only because I dramatically backed off on my efforts.

It's important to recognize the symptoms -- either in yourself or others. I really appreciate the volunteer who walked with me for a bit to make sure I wasn't continuing to overload myself.

This race, and my previous crash and burn in San Diego, both came as surprises to me. I say this because running in the heat never used to be a problem for me. You see, I grew up in Phoenix Arizona. I was acclimated to some pretty brutal conditions. I used to run at lunchtime in the summer -- 110 degrees. But after moving to Prescott, Arizona (cool and dry), and then to the Kansas City area (hot and humid in the summer, but cool in Spring and Fall, cold in Winter), and finally to Massachusetts (where I almost never ran in warm temperatures), I had totally de-acclimated from the heat. And oddly enough, I am beginning to believe that I have been chronically dehydrated.

Now that it has gotten quite warm here, and I am consciously trying to drink more water, I'm realizing how much water I have NOT been drinking over the past 10 years. This week I've been hydrating like crazy and am recalling how, in Arizona, I would drink water almost continuously. And I remember 10 years ago when we moved to the Kansas City area, commenting to others how I don't seem to be drinking nearly as much water as I used to. Chronic dehydration. Not good for marathoning anywhere.

And so now I am consciously acclimating myself to hot weather running. I am again drinking vast quantities of water. And I am running in somewhat warm and humid weather.

The experts say it takes 10 to 14 days to acclimate to the heat. In the first week, there is an increase in blood plasma, heart rate reduction, and improved cardiac output to capillaries in the skin and active muscles. In the second week, the blood plasma levels return to normal and there is a longer-lasting reduction in skin blood flow that serves to increase central blood volume. The bottom line is you sweat more and you sweat earlier. The effect of all this is an increased tolerance to exercise in the heat -- you can run farther (or faster) with reduced cardiovascular, thermal and metabolic strain. Good stuff.

On Friday, I did 6 miles on the trails at lunchtime. It was warm. It felt great. Averages 8:54 per mile. Saturday morning I did 4 miles around Fresh Pond. It was early and the weather, though a little humid, was pretty nice.

C-Ya (and take it easy in the heat)


Blogger E-Speed said...

glad you're acclimating and hydrating! I drink a lot of water religiously!

6/24/2006 8:02 PM  

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