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Posted on November 20, 2013
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Exposure to Cold and how it sucks!
In my opinion, the most difficult part of this last weekend’s Go Ruck was the soul crushing cold we endured. After jumping in the ocean at roughly 2 AM we were instructed to perform various drills and exercises on the beach, each of us shaking like crazy as we tried to warm ourselves a la March of the Penguins. I soon found myself using what little brainpower I had left to consider our bodies’ physiologic responses to the cold, one of my favorite subjects that I came across during my undergraduate studies. Considering that winter is upon us and with it a whole slew of cold stressors, I thought a few posts detailing these effects might be fun. So, as Mario would say, here we go!
Post #1: Insulation
Homo sapiens (that’s us!) evolved near the equator where we have a much greater chance of dying from heat stroke than from hypothermia. Our bodies have therefore been shaped and outfitted to deal with the heat (that’s a post for another time) but are rather poorly equipped when it comes to surviving the cold. So when humans first migrated out of their birthplace in Africa and into the much colder, less hospitable Europe around 70,000 years ago, they relied largely on their ingenuity to overcome the life threatening cold they faced. That is, they developed clothes.
Clothes serve as a buffer between the human body and the outside world. The heat that we generate from our metabolism can be trapped beneath layers of animal skins, plant-based woven textiles, or Luon to keep us warm despite the surrounding temperature. Although humans are (debatably) the only animals that wear clothes, we are merely mimicking a method of cold survival that has been around a lot longer than we have: insulation via fat.
Ever wonder why whales have so much blubber? I know I have (ISN’T SWIMMING SUPPOSED TO BE THE BEST FAT BURNING EXERCISE IN EXISTENCE?). Whales developed their fatty bodies to protect themselves from being in the cold, cold depths of the ocean. Fat insulates them, providing a buffer for heat flow out (or in) to their bodies from the surrounding waters. Fat does the same thing in us. There are many reasons why humans need fat on their bodies, and one important one is to protect us from the cold. In cases of progressed anorexia, in which the body loses most of its fat stores and thus most of its insulation, people grow long, silky hair called lanugo over the entirety of their bodies, including their face—the body’s attempt to protect itself against cold unfettered by fat. Humans store their fat primarily around their torso, where its insulating properties are best used to protect the vital organs encased there.
That brings us to two methods of battling the cold: insulation via clothes and insulation via fat. But there is another form of insulation, a more active response to cold than the previous two, called localized vasoconstriction. Vasoconstriction, or blood vessel narrowing (vaso = blood vessel, constriction = …constriction), allows the body to pick and choose where it sends its blood by clamping off certain blood vessels. There are many things that our blood transports, but for the topic at hand lets consider blood a carrier of heat. That means that our body can manage its temperature by managing its blood flow via vasoconstriction. This is most obvious in our response to heat: we direct our blood to our skin so that excess heat may be wicked away by the surrounding air, which works in concert with the cooling effects of sweat. This is why our skin appears red (more blood flow to it and therefore more blood/the color red in it) when it is hot.
Heat transport via blood flow is less apparent in our response to cold, but it is most definitely still hard at work. When the outside air puts our bodies at risk of cooling down to dangerously low temperatures, localized vasoconstriction is employed to retain and prioritize warmth. As is expected, the body responds in the opposite way to cold as it does to heat, pulling blood away from the skin so that heat is not wicked away by the environment. This is why cold skin appears white, as it has been drained of much of its blood. Additionally, this relocation of blood serves to prioritize the body’s limited heat, sacrificing the extremities (arms, legs) to maintain healthy temperatures of the vital organs in its core/torso (heart, liver, etc.). This is why our limbs become sluggish, numb, and awkward when we are cold: they are lacking the blood necessary for proper function. This is also why frostbite (tissue death due to cold exposure) most often occurs only on extremities like fingers and toes.
So while we still need clothes and outside warmth to survive in the majority of places that humans live these days, we still have a couple of tricks up our sleeve that we use to make it through the winter (or the Go Ruck). I’m not sure if you all find this stuff interesting, but I certainly do! I guess that’s why it was all I thought about while becoming a human popsicle on the beach last Friday night/Saturday morning. There’s a bit more to talk about concerning our physiologic response to the cold, but I’ll save that for some future posts.
Thanks for reading! - Jonji.
Random Fact for the Day
An Olympic gold medal must contain 92.5 percent silver (ironic!)
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