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Overheating Because of Moisture-Wicking Fabric: Could This Have Caused the Bighorn Catastrophe?

Posted by on Jul 12, 2012 | 26 Comments

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]

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.]






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  1. Angie bee
    July 16, 2012

    So this seems like with reason applied to the idea of sweat wicking material that we are being duped by gimmicky shit!
    I am having a real issue with keeping my core body temp down. I have found that loose cotton is much cooler and allows me to sweat which gives me the cooling effect. I also love my misting spray bottle. I couldn’t get the full benefit of it in a wicking shirt.

  2. Chris
    July 13, 2012

    Maybe the issue is that the tech shirts wick away the “water” of the sweat via their fibers but the “heat” of the sweat stays or is retained at a higher rate than with no shirt or non-tech those shirts. Also how does the body’s core and surface tempatures interact with each other and your overall performance? Are they one way streets where core heat goes up and out via the surface and/or does a higher surface temp eventually lead to a higher core temp? Are we dealing with two sets of laws; thermo and hydro-dynamics?

    • Jason
      July 13, 2012

      For the scientific answer, see edit #2 above.

      As far as performance, it goes down as core temperature increases. Surface temperature will always increase with exercise in an attempt to dissipate heat. Core temperature is kept lower by diverting warmer blood to the surface of the skin where it’s cooled via evaporative cooling of sweat, and is them diverted back to the core. Think of your skin as a radiator of sorts.

  3. Ed
    July 13, 2012

    I have been struggling in the DC heat over the last few weeks with wicking tshirts. I feel way overexerted given the mileage and pace, even factoring in the high heat and humidity. Today I ran shirtless and felt the best I have in months. Men, you have nothing to lose but your shirts. Ladies, go for it.

  4. Dave
    July 12, 2012

    Nice theory, but may not be supported by the laws of thermodynamics. Your sweat acts as a heat pump carrying heat to the outside of your body. Whether the evaporation occurs from your skin or from your shirt should not make a difference on how much heat is being released. The act of evaporation (increasing the kinetic energy of the water molecules) will however decrease local temperature so as to obey laws on conservation of energy. Whether that cooling occurs on the surface of your shirt or skin may make a difference as to perceived cooling. Maybe shirtless is the most efficient then?

    I dunno. My last thermodynamics class was an 8am class, and I was known to sleep through them from time to time.

    • Jason
      July 12, 2012

      Saturated tech shirts seem to cool more than non-saturated tech shirts. The big question- how does the evaporation from the surface of the shirt affect the underlying skin in both conditions? I’m hypothesizing that the non-saturated shirt creates a barrier of trapped air in the fabric, which inhibits heat transfer from the skin to the evaporative-cooled surface of the shirt. Does that really happen?

      • Adam Lawrence
        July 13, 2012

        I’m no expert, but Dave’s post sounds right. As long as the water escapes your body in liquid form then evaporates, it will carry body heat w/ it. It seems that you’re right, and the non-saturated shirt will have more space for air: it is less dense (both b/c non-saturated, and b/c synthetic materials tend to be much less dense than biological ones), and it will not cling to your skin the way a saturated shirt does, hence allowing more air to accumulate between your skin and the fabric. Another issue, however. is “wetting out”: as the shirt becomes saturated, and thus heavier and denser, the ability of both water and air molecules to move through it is inhibited, hence the experience of running through a warm summer rain w/ a soaked shirt while feeling uncomfortably hot and sweaty.

        • Dave
          July 13, 2012

          Following up on the ‘wetting out’ issue, if your sweat drips off of you, you are not going to get the evaporative cooling benefit, so you’ll have to drink more to keep up a given heat dissipation rate. The idea of wicking shirts is to bring your sweat quickly to the large outside surface of the shirt to expose as much of it to simultaneous evaporation as possible, and hence a higher heat dissipation rate.

          A non-wicking material will trap more sweat between your shirt and skin, leading to more of it to run off of your body due to gravity – hence you miss out on evaporative cooling.

          • Jason
            July 13, 2012

            I’m pretty sure wicking material was first developed as a means of warming, not cooling. They were used by hikers that would sweat while moving, then stop. In non-moisture wicking clothing, they would get cold due to the evaporative cooling effect coupled with the loss of muscle-generated heat from standing still. The material prevented this problem by creating a barrier of trapped air between the skin and the moist surface of the material so the evaporative cooling cooled the surface of the shirt but not the underlying skin.

            This effect is negated if the material is saturated because the sweat is a much better heat conductor than the trapped air. The sweat evaporating off the surface of the shirt will remove heat from the body, just like it would in a cotton shirt. Because of this, you’ll still get cold when wearing a drenched moisture-wicking shirt when ceasing activity. If it is not saturated, you’ll stay warmer.

          • Adam Lawrence
            July 13, 2012

            Both of these ideas seem to make sense to me. I had never considered the possibility that these materials would keep you warmer when not saturated, by trapping air and preventing sweat from evaporating (or dripping) off your skin directly. There must be some heat loss even when the water stays in liquid form and doesn’t vaporize as it leaves your body, right? After all, the sweat is already carrying heat when it emerges from your pores. Does evaporation actually remove more heat from an organism than removal in liquid form? Obviously, the vapor is warmer than the liquid, but some of that heat is donated by the surrounding air, nor the organism (I think). Is the amount of heat removed through evaporation actually greater per unit water, or does evaporation simply alow more warmth to be removed (via more water removed) per unit time than removal via falling drops?

        • Michael
          July 13, 2012

          It does matter if the water evaporates from the skin or the shirt, it is the act of evaporation that cools, rather than simple heat transfer. Think about an evaporative AC unit, or, when you get of the pool on a cool day, you can stay warm by drying yourself (tech top style) but if you don’t dry yourself, you will very quickly get cold through evaporation. About tour de France cyclists, many of them wear an undershirt in hot weather, you can see it when they open their tops up. Personally, I’ve found the merino wool top the best for all weather, except high humidity where they get very heavy!

      • Brian G
        July 13, 2012

        Dave is correct but only if the shirt is immediately adjacent to the skin. If you have a big, loose tech shirt that flops around, soaking up your sweat like a sponge when it brushes against you then lets it evaporate from the shirt while it’s flapping loose, then only the shirt will get cool but not your skin. (Remember, these quick-dry tech shirts are usually advertised as keeping you “dry and comfortable”.)

        Another simple way to think about this: pull your shirt away from your skin and press an ice cube against the shirt. Do you feel any cold on your skin? Now hold the shirt tight against your skin and repeat. Now do you feel the chill?

        • Jason
          July 13, 2012

          Good demo, Brian. I added a bit more of an explanation of how humans cool off in the original post, too.

  5. Paul Joyce
    July 12, 2012

    Jason, interesting post. I live in a hot/warm climate (most of the year) and wear merino wool tops when running, which initially felt counter intuitive. But they work really well even on very hot days.

  6. MC
    July 12, 2012

    How do you combat the chafing from the cotton shirt? whenever i used to wear cotton, my armpits/lats used to get chafed from that seam. Even if it was looser. If i remember correctly, i had to cut the sleeves off my shirts, and that helped a little. Do you wear a tight or loose cotton shirt?

  7. Chris
    July 12, 2012

    If this is so, then what would be the impact on guys in the Tour De France – especially with the increased evaporative effect of wind and altitude? they traditionally used Wool back in the day. Interesting to investigate for correlation(s)?

  8. Shane D.
    July 12, 2012

    Its never good to interfere with the bodies natural mechanisms, especially to cool the body. I had the same issues with moisture wicking shirts. It’s funny how many companies are making “dry cotton” shirts now and changing their tunes on the “cotten is rotten” adage. When I switched to dry cotton, I found I didnt overheat in races.Maybe we should all run barefoot AND naked!

  9. John White
    July 12, 2012

    Moisture-wicking shirts work well if you dump water on them to keep them moist. I just did several long runs and rides in hot dry weather and it worked beautifully. The air coming through the shirt and hitting the skin is cold IF the shirt is moist.

    That said, I don’t think I’ve ever managed to soak a shirt with my own sweat such that it provided this cooling effect. I have to dump water to cool off. So, you might be onto something. Initially I said “Heck no” but you might well be onto something…

  10. Johnny boy
    July 12, 2012

    I like the last bit because it gets me a little closer to running naked! Going to make my own loin cloth now.

  11. Kelly Mahoney
    July 12, 2012

    This is the second time in the past week I have heard about Noakes going against dogma. He was recently interviewed about his recent conversion to the Atkins diet:

    Much of what Noakes says comes straight out of Taubes’ books. He tells people to rip out the nutrition section in “Lore of Running”. In fact, he said he will rewrite the book. The podcast host, Jimmy Moore, compared Noakes to Mark Sisson, which Noakes appreciated. Personally, if Noakes likens himself to Mr. Chronic Cardio, I don’t see the point of rewriting “Lore of Running”. He should just disassociate himself from the book.

  12. Andy
    July 12, 2012

    I’ve always had a moral objection to unnecessary shirt-wearing… if it’s above 60 and you’re running, you don’t need a shirt. period.

    • Rich Frantz
      July 19, 2012

      2 words…deer flies

  13. Rebecca @ Runner with an Appetite
    July 12, 2012

    I’ve read a lot about runners who wear tight, white long-sleeved shirts during their ultras. They wear them so their sweat is immediately absorbed and they feel cooler. I have been suspicious about this since I always thought we got cooler when we let our body evaporate the sweat. Your post helps me to think I may be on to something!

  14. Tuck
    July 12, 2012

    The whole point of moisture-wicking shirts is to prevent evaporative cooling of the skin. So I’d say it’s a lot more than “plausible”, it’s the expected behavior. And yes, everything’s obvious in hindsight. 🙂

    I also don’t wear them when it gets warm, or if I start to feel overheated. I’ll often wear them at the beginning of a race, and pull it off part-way through.

    Ultra-light wool might be a decent substitute, as it will still keep you warm at the beginning, but keeps the moisture next to your skin, where it can help cool you, much like cotton.

  15. Seamus Foy
    July 12, 2012

    I have huge issues with hydration. I easily put down triple to quadruple the fluids my running buddies consume, and I still feel a brutal thirst to keep drinking. It does seem to be a bit better when I run shirtless. I’m starting to think that at any temp above 60, a shirt really serves no purpose, other than to chafe nipples.

    I’m gonna try it a lot this summer and see how it goes, then I’ll occasionally wear a moisture wicking shirt to compare.