Friday, October 26, 2007

Eating and hypothermia

Date: Oct. 26
Mileage: 32.5
October mileage: 573.4
Temperature upon departure: 39
Rainfall: 1.36"

I had a cold-weather epiphany today: The secret to staying warm is staying fed.

It seems pretty simple, but it hadn't really occurred to me how important fuel is to the whole equation. I've been reading different accounts of people who contracted hypothermia while mountain climbing. In many cases, they were bundled up and climbing fairly strong. The temperature didn't change. The weather didn't change. One minute they were fine, and the next minute they were hypothermic. What happened? Does hypothermia really strike at random? Without warning? The whole idea was very scary.

Here in Juneau, during the fall monsoon, the temperature drops very slowly over time as the wind gradually picks up strength. It gives off the illusion of consistency, but there is change. By late October, the tail-end of the monsoon, the daily high temperatures have dropped from low-50s to high-30s. The 15 mph south winds gusting to 25 are now 25 mph south winds gusting to 50. If I was transported through time from early September to late October, I would likely change my habits drastically to match the change in weather. But when the cold weather settles in over weeks of barely-detectable increments, I may add a layer here and there, but I do little else differently.

However, the 30-mile rides of early September were not the same as the 30-mile rides of today. I set out with the same goals and the same destinations, forgetting that now the same distance takes longer, seems harder, and generally consumes more energy. What I feel at the end of these rides is cold. Sometimes it's a barely noticeable drop in my core temperature. Sometimes it's enough to spur shivering ... mild hypothermia. I thought the causes were failures in my clothing system. The next day I would add layers that I usually ended up getting rid of because I would overheat early in the ride. But today I tried something different ... something I don't usually do ... I set out on a 30-mile road ride with an Clif Bar in my pocket.

Chugging straight into a headwind at a screaming pace of 9 mph during my return ride, I caught the full force of a monster gust that nearly stopped me completely. I had to click out of my pedals to keep from tipping over. An amazing gust - the kind that sucks the oxygen right out of my lungs and leaves me gasping and sputtering. I could feel the wind tearing through my layers, prickling my skin and chilling my torso. The cold was already setting in, and I still had seven slow-moving miles before I would be home. It seemed a good time to eat the Clif Bar.

After that, I perked up considerably. My pace picked up; my body started to produce heat again; I could feel the core fires flare and beads of sweat began to form on the back of my neck. A few more monster gusts slowed my pace to 5 mph at times, but they didn't stop me. It finally made sense - it's been true all this time. I hadn't become overly susceptible to the mild cold of the fall monsoon. I had bonked.

When I came home, I finally began to leaf through the promisingly thorough but deathly boring medical booklet I recently picked up, "Hypothermia, Frostbite and Other Cold Injuries."

"In wilderness environments, hypothermia results from:
1. Inadequate protection from the cold.
2. Inadequate fluid intake resulting in dehydration.
3. Inadequate food for metabolic fuel to be burned during exercise."

Without caloric replacement, the body becomes much less efficient at regulating its own heat. It begins to tap fat stores to keep organs and muscles functioning, but these sources of fuel are too slow-burning to be efficiently used to produce heat. So even the early stages of a bonk can be dangerous at low temperatures. One of the first remedies the medical book recommends for a mildly hypothermic person: Sugar drink (one of the most quickly metabolized sources of fuel. Interestingly, the book said it doesn't matter if it's hot or cold. Hot drinks do little in the longterm to warm the body's core temperature. They just feel good.) Once you've had the sugar, embrace the urge to shiver violently. And try to commence exercising. The body can bring itself back from hypothermia, as long as it has something in the tank to burn.

Interesting. It seems so simple, but this is a real breakthrough for me. It's inspired me to take more stock of my energy level and food intake while riding. Bonking is annoying in the summer; it can be deadly in the winter.

10 comments:

  1. This is one of the things I teach in my winter camping classes I lead. Keep the furnace stoked. If you don't continually stoke the furnace with fuel (food), the fire (or warmth) eventually goes out.

    My moment of epiphany was when we were thru-hiking the AT. It was March in the Smoky Mountains, we had had a snowstorm with 1 1/2 feet of snow followed by night time temps in the single digits. We made it to a trail shelter for the night. After stopping I started to get cold and my toes went numb. We quickly made some dinner. As I was finishing my meal I literally felt the warmth return to my toes. Nothing had changed except I had eaten a bunch of calories. I was still sitting outdoors and the temp was still 9F degrees. Prior to that experience it had never crossed my mind that the simple act of eating could warm me up.

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  2. I've never had hypothermia, but I didn't make this connection either until someone reminded me of the definition of a calorie:

    From Wikipedia

    A calorie is a unit of measurement for energy. Calorie is French and derives from the Latin calor (heat).

    The small calorie or gram calorie approximates the energy needed to increase the temperature of 1 gram of water by 1 °C. This is about 4.184 joules.

    It's kind of a duh moment when you think about it like that. Glad you made the connection! I'd never last biking in the crazy conditions you go out in. I salute you and I will continue to enjoy the pretty pictures from my nice warm house. :)

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  3. I work a lot with endurance athletes to perfect their nutrition intake for races...in the winter months it's really important to pay attention to hydration and food intake.

    While you may not sweat as much, you loose a lot of water due to the fact you are breathing cold air. Cold air must warmed and moistened as it travels down your throat and into your lungs.

    You will also lose more water through an increase in urine production. The body wastes energy keeping urine warm...so that's why you pee more in cold weather...to conserve energy.

    Your caloric intake will also increase...why? Essentially because you are wearing more clothes and riding a much heavier bike...not to mention carrying the appropriate gear. So your increasing your workload which will require more calories.

    Almost done...people eat more in the winter because I by prodect of metabolism is heat production...so by eating you actually help warm your body...it's called the thermic effect of food. It's also why you don't want to eat when it's so hot...because by eating your body is creating more heat...the last thing it wants to do.

    Hope this helps a little...if you need some nutritional advice let me know :-)

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  4. I had that same sort of epiphany on one of my winter backpacking trips a few years ago, so now when I go out snowshoeing or camping in the winter, I'm constantly snacking.

    That's the key for me - snacking. When I'm hiking with a loaded pack or pounding out the miles on the bike, I hate eating large chunks of food like cliff bars, etc. So when I hike I keep baggies of trail mix in my pocket and constantly dig into those. That way I keep the calorie count up, but never feel like I'm inundating my stomach w/ a mass of food that's just going to make me feel lethargic. On the bike I usually opt for power gels, but end up using clif bars, too, on longer rides, as after a while gel gets old.

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  5. I once bonked so bad that even though it was in the upper 50s, I sat for an hour with a jacket and 2 blankets and I was still shivering. The biggest problem is that once you get too cold your brain slows down and you have trouble figuring out what's going on. I once was really hypothermic when I was riding and I slammed my brakes a block after a car turned in front of me. Eventually think they're hot and start stripping their clothes.

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  6. also think in terms of hours out not miles traveled!

    coca cola from a gas station always seems to do the trick for me...

    Got so cold 3rd day in on the GDR that took me 8 hours to get warm again. Partly do due to not stopping to eat something!

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  7. My friends laugh at me as I stuff m & m's into the deepest reaches of my bag -- the last defense against hypothermia ...

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  8. This just happened to me on a road ride a few days ago. This time of year, I always forget that I need to eat almost twice as much on the bike as in the summer. I was on the edge of bonking when we stopped at a store for food. Ten minutes off of the bike and I felt my body temperature drop like a rock. I stuffed down a muffin and a bag of M&Ms while shivering violently, and after 15 minutes back on the bike it was like nothing had happened.

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  9. I found some interesting information about Hypothermia here. Check it out!

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