Thermoregulation and Running: A Cool Idea

The Evil Moisture Wicking Clothing?

In a previous post, I theorized about the role a moisture-wicking shirt played in three crappy runs over the last seven months or so. After reading your comments and doing a little research, my “ah-ha’ moment wasn’t quite so revolutionary. The conclusion is pretty obvious:

Moisture wicking clothing does more harm than good for runners in hot weather.

The reasoning is simple- the mechanism of drawing moisture away from the skin thwarts the process of evaporative cooling of sweat. In other words, the wicking of the moisture means the sweat evaporates on the surface of the shirt, not your skin, so we’re robbing our body of one of the primary cooling mechanisms used to reduce our core body temperature.

The video from Sports Science explains the idea nicely, though I seriously question whether the X Bionic fabric would be as effective as bare skin.

Indeed, the marketing material from several moisture wicking companies confirms this. They are very guarded about saying the fabric cools you down in heat. Instead, they tend to use statements like “the fabric makes you feel more comfortable.” Indeed, moisture wicking fabrics are great… when you’re not generating a ton of heat via exercise.

My new rule of thumb– I’m only using moisture-wicking fabric in cold weather or in warmer weather when my activity level is low enough where body temps can be maintained without the sweating mechanism.  If I am running in hot weather, I’m going with white cotton or no shirt at all.

Sidebar- the shirtless option may also have another benefit- prevention of internal cancers. Check out this article, and note the citation from Dr. Gordy Ainsleigh. We did a run with Gordy last week and he was, of course, shirtless.

Thermoregulation: My Missing Link

Over the last few days, I’ve been experimenting with perceived body temperature and how it makes me feel. I believe my problems at Bighorn, the disastrous Boulder to Nederland run, and Across the Years were all caused by overheating.

During each of those events, I knew heat was the problem… indirectly. I assumed I wasn’t drinking enough (dehydration) or I wasn’t taking enough electrolyte supplementation (hyponatremia). These are the two often-quoted causes of the symptoms I was experiencing. In fact, most runners recommended either drinking more or taking more electrolytes.

The feelings I was having weren’t quite right, though. In training, I have purposely run to a point of dehydration. Early in my running “career”, I also experienced the early signs of hyponatremia. Neither of these feelings were quite the same as I experienced in these three instances. There was some other variable I was missing.

That variable was a rising core body temperature.

Generally I’m a pretty good hot weather runner. I can tolerate heat far better than cold. In the humid Midwest, I used to run on the hottest of days with no issues at all. I didn’t experience this problem until I started running in hot, dry weather… and then only when wearing moisture-wicking shirts.

As I explained previously, the moisture wicking material apparently caused my core temperature to rise faster than my sweating mechanism (and passive heat-dissipation methods) could get rid of the excess. The result was extreme fatigue, dizziness, and severe cramping, all of which can be explained with Noakes’ “central governor” theory- my body was fighting me to stop moving to prevent, well, death.

In all three cases, I didn’t have signs of dehydration or hyponatremia. As such, drinking more or consuming electrolytes had no effect. What did help, however, was getting out of the sun and stopping activity. THAT allowed my core temperature to cool.

Some basic experiments seem to support this theory. I did two runs up a mountain. The mountain had several “micro-climates” of various combinations of sun exposure and wind. The goal was to try to replicate the feelings of fatugue, dizziness, and cramping without having to run a crazy long distance. I accomplished this by running at a strenuous pace up the mountain. I made sure I was adaquately hydrated and electrolytes were supplemented before the run to help rule those out as confounding variables. I carried one water bottle and drank to thirst throughout the run, which equaled about 12 ounces per hour.

The Results

I was able to mimic the exact same feelings I had in the three disastrous runs, though to a lesser degree. The symptoms were worse in sun-exposed areas with no wind, improved in the sun-exposed areas with wind and shaded areas with no wind, and completely disappeared in shaded areas with wind.

I was shocked the results were so clear. Previously, I was at a complete loss as to the cause of the symptoms because I didn’t consider body temperature to be a variable. It was never an issue in years of prior running, even when air temps were very high.

As soon as I recognized body temperature as a variable, the correlations became obvious. If sweat isn’t cooling me down, performance suffers. A lot.

The Solution

The solutions are obvious. I have to work on methods to stay cool. Here are the steps I will take:

• Train in heat more often. Theoretically, this will help make the body’s thermoregulation system more efficient. At the very least, it will help train me to recognize the early signs of overheating.
• In hot, dry weather, go shirtless. This will maximize evaporative cooling.
• If there’s a lot of sun exposure, wear white cotton shirts. The white cotton will absorb less heat than my slightly tanned skin. The cotton, when saturated with sweat, will allow evaporative cooling via conduction. I don’t think it is as efficient as bare skin, but it is far better than the moisture-wicking materials I’ve used previously. Also, I’ve run in cotton in the same hot, dry environments with no issues at all.
• During a race, take advantage of cold water (from aid stations or streams) and ice/snow by wrapping it in a bandana and placing it around my neck, dumping it over my head, or some variation of submerging myself. This will cool the body via conduction.
• If all else fails, slow down. Since movement generates heat, a lack of movement will cool the body quickly. I won’t be so stubborn with stopping in the future.

I’m very confident going into my next two hot, dry races (Grand Mesa 100 in western Colorado and the Trans-Rockies stage race across Colorado). Both will feature hot temps and a lot of sun exposure. By implementing these solutions, I should see a significant boost in performance. At the very least, I’ll be familiar with body temp as a potential problem-causing variable. This should help me regulate both hydration and electrolyte levels, too, because I won’t erroneously blame them for issues caused by overheating.

In essence, we have to start treating thermoregulation as a separate variable that’s not necessarily controlled by drinking more or popping more salt tabs.

I know a few of my readers have been experimenting with ditching moisture-wicking clothing in hot, dry weather. Any feedback yet? What about thermoregulation? Does anyone have any other useful tips?

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