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.