Hi y'all...

This weekend I had the opportunity to give a presentation on cold weather injuries to a large group of Boy Scout leaders and a smaller number of older scouts. I used the same slides that I used for my presentation last year, but this year I spent a great deal more time talking about hypothermia and it's prevention. The message that I really wanted to impress in their minds was that hypothermia is not so much about being exposed to cold as it is a caloric deficit.

When I participated in that hypothermia experiment last spring, what really caught my attention was that my subject began showing significant signs of mental deficits, poor decision making, and a frighteningly sudden comfort level with the extreme cold he was experiencing (he was wet, laying almost naked in the snow) and yet his core temperature had only dropped to 97.2º. Technical hypothermia does not begin until the body reaches a core temperature of 95º (characterized by the "umbles", intense shivering, poor decision making), so why did our subject show signs of mild to moderate hypothermia (shivering mechanism was begining to fail, poor judgement, comfortable in the cold) when he was still so warm? The quick and easy answer is that he had shivered through his readily available muscle glycogen stores and his brain no longer had the glycogen it needed to function optimally. The caloric cost of intense shivering is 220 kCal/hr, and our guy was shivering hard for at least an hour, if not more. That is on top of the ~70kCal/hr or so he needed for his basal metabolism, and the maybe 10-15 kCal/hr he needed to warm the air he was breathing in.

So, to me, the most important take home point is that not only does the body need readily available calories to function at rest, but it also needs calories to provide warmth to the extremities (the heart is a muscle, afterall), and allow the brain to function optimally. Combine the cold with heavy winter exercise (everything you do in winter takes more energy) and you can see how the need for readily available calories (i.e. carbs) increases dramatically... i.e. you can easily double your caloric need when winter camping/hiking/snowshoeing, etc. When you don't take in enough calories, the body doesn't have the tools it needs to avoid the caloric-draining effects of the cold. Hypothermia happens when the brain stops being able to make clear decisions (i.e. move around, eat, put on more clothing, get out of the elements), and that is more dependent on calories than cold.

Bottom line... EAT! Drink too... hydration is at least as important as food.

MNS