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Thermoregulation: An Overview of Heat Loss Mechanisms and Practical Guidelines for Staying
Warm with Lightweight Gear
by Ryan Jordan | 2003-10-24 03:00:00-06
Excerpted From: “Lightweight Backpacking: A Field Guide to Wilderness Hiking Equipment, Technique, and Style,” Ryan Jordan (Ed.). Beartooth Mountain Press
The literature on physiological thermoregulation and clothing’s effect upon it is already vast. If you’re interested in a comprehensive review of thermoregulation in an
outdoor context, refer to the excellent
Secrets of Warmth (Hal Weiss, The Mountaineers, 1992). This article focuses primarily on specific classes of apparel, shelter,
and sleep systems for cold, wet conditions. We’ll cover clothing systems for hot and dry weather elsewhere. Specifically, this article covers three major topics:
mechanisms of heat generation, mechanisms of heat loss, and the design of equipment to minimize heat loss.
Mechanisms of Heat Generation
Even in cold conditions, heat generation can be a problem:excess heat generation resulting from vigorous activity can result in sweating that leads in turn to rapid
evaporative cooling and the eventual breakdown of the body’s thermoregulatory capacity. We’ll consider this problem later. For now, let’s assume that conservation of
every bit of the body’s heat is a desirable condition, and address the primary means by which the body gains heat in cold conditions.
Your best source of heat is generated internally by your body’s metabolic engine, fueled by calories gained from the metabolism of food. When you reduce caloric
intake, you can reduce your body’s ability to produce heat. In a recent alpine climb in Wyoming’s Teton Range, Alan Dixon and I spent 38 hours without sleep and
with only enough calories for a twelve-hour climb as we engaged in a difficult descent out of a summit snow and ice storm. By the end of the route, as we were
approaching our car on a sun-warmed trail in sixty-degree temperatures at the valley floor, we were still shivering – while wearing our PolarGuard 3D-insulated belay
parkas. Our metabolic engines, which had been fueled by more than 300 calories per hour for the first twelve hours of the climb, had slowed to a crawl.
Trying to calculate the proper number of calories needed for a given level of exertion while simultaneously accounting for environmental factors such as temperature,
wind, and precipitation, is a futile exercise. The National Outdoor Leadership School (NOLS) has devised elegant predictive models for caloric consumption that
significantly overestimate the amount of food required for most individuals. This results in extra comfort, but not necessarily extra safety. Consider that the two to five
pounds of extra food could be better spent on warmer insulation, or dropped from a pack altogether to reduce the energy expended to carry the extra weight: such