Timothy Noakes, author of the book Lore of Running, has released a new book about the problem of over-hydration in endurance events. Waterlogged has created quite a stir among one of my favorite communities. I haven’t read the book yet, but have read enough commentary to get the gist of Noakes’ central theme- we drink too much in races. His recommendation- drink to thirst.
[Check out this summary from Joe Uhan over at irunfar.com]
My recent experiences could be explained by this phenomenon of over-drinking. In the past, I drank too much. It wasn’t unusual to drink so much I urinated at least once every hour. Realizing I was spending too much time watering the flora beside the trail, I started to cut back. My finish times decreased as expected. Unexpectedly, I started feeling better during the races. This would seem to fit with Noakes’ hypothesis.
While that was an interesting development, it was Noakes’ point about thermoregulation that made me pause. His idea is pretty simple- the body attempts to maintain homeostasis by keeping body temperature at normal levels. Exercise generates heat. Your body combats this with the evaporative cooling of sweat. In the event body temperature rises, other mechanisms kick in to regulate body temperature… namely a reduction in pace.
Ever run with a dog in hot weather? They’ll run fast until they can no longer cool themselves. Then they stop. They can’t be compelled to continue on until their body cools.
At Bighorn, I ran relatively fast in hot weather. This isn’t new; I do this in training regularly. At some point, though, I started cramping badly. Running became impossible. I struggled to explain why this occurred. I wasn’t dehydrated, and didn’t have an apparent electrolyte imbalance. The cramping shouldn’t have been a result to working too hard, I should have been well-trained for the task at hand.
Then I made a connection.
This has happened three times since the beginning of the year. All three cramping events happened in hot, dry weather. In two of the three occurrences, dehydration and electrolytes were non-issues (I had an adequate supply of both). The one common denominator?
I was wearing a moisture-wicking shirt.
Here’s the theory- moisture-wicking materials, by definition, wick sweat away from the skin before it evaporates. If the sweat doesn’t evaporate off skin, no cooling occurs. If no cooling occurs, body temperature rises. The body fights this by limiting pace, first by fatigue. In all three occurrences, I felt unusually fatigued based on the distance traveled. Normally that would be enough to cause me to stop. However, since it was a race, I continued on. The body’s next attempt to get me to stop- severe cramping.
Yup, that worked.
In all three cases, the symptoms abated once the temperatures cooled.
So was it really the moisture-wicking material? I have more evidence.
In training, I usually wear cotton shirts. Same deal with races. Unlike moisture-wicking materials, cotton gets soaked with sweat and sticks to your skin. When the sweat evaporates, the skin is cooled. I’ve never had the cramping problem wearing cotton.
Furthermore, I’ve worn moisture-wicking materials in hot weather in the past with no issue… in Michigan. The humidity prevented the immediate evaporation of sweat off the material, so it became soaked and stuck to my skin… just like cotton. In essence, the humidity thwarted the effectiveness of the fabric. The dry climates allowed the fabric to work as designed, which led to overheating.
The solution may be much simpler than I assumed. I spent weeks trying to figure out how to manipulate hydration and electrolytes to prevent the problem. Instead, the problem may be fixed simply be going back to cotton shirts. Better yet, go shirtless.
So far, my early experimentation has confirmed this. Avoiding moisture-wicking materials in the dry heat has worked. I’ll continue to experiment with the concept, but the true test will be the Grand Mesa 100 miler in a few weeks.
What do you think? Is the idea plausible?
[Edit- check out this interesting vid from the show Sport Science:
Of course, I'd like to see the X Bionic clothing compared to bare skin... I suspect skin would still be more effective at dissipating body heat.]
[Edit #2- some have been commenting about the exact mechanism the body uses to cool itself. There are several. If the exterior temperature is less than the body temperature, the body will radiate heat into the environment. If there's air moving over the body, heat will be removed via convection. If something is contacting the skin (like an ice pack), heat is removed via conduction. The body also cools itself by sweating and diverting blood toward the skin. The evaporation of sweat requires heat energy, which cools the skin and underlying blood, which is then used to keep core temperature lower.
The problem with the tech shirt is it eliminates the evaporative cooling effect by moving sweat away from the skin. The blood isn't cooled and the body core temperature rises. If the tech shirt is saturated, the evaporative cooling effect is somewhat restored due to heat conduction from the skin to the surface of the shirt.]