"The problem with winter sports is that they generally take place in winter" -- Dave Barry

I'm not a huge fan of cold weather, and perhaps the only bright spot (for me), in the dystopian climate changes we're experiencing is that winter ain't what it used to be. But while I'm writing this on a sunny January day with temps in the mid-40's (F), cold weather still happens, and the nether regions of New England and the midwest still do get real winters. So let's talk about being safe in the cold weather. I already talked about frost bite, now let's move on to hypothermia. 

Hypothermia is defined as having a core body temperate of less than 35C (95F) and can initially be associated with shivering and confusion. As body temperatures continue to drop, shivering will increase and then may stop while the confusion can get worse and worse, leading to possible paradoxical undressing and coma. 

Your body's normal temperature range should be somewhere between 97°F (36.1°C) to 99°F (37.2°C). If you start to go out of that range, your body will work to bring it back to normal, with opposite responses to either store or eliminate heat. 

Body heat is a byproduct of metabolism and the majority of our thermogenesis comes from the liver, brain, and heart, but mostly from skeletal muscles during exercise.

In brief, when you exercise, your muscles generate heat and that heat is brought to the surface of the skin via blood vessels, and heat is released through radiation, convection, conduction, and evaporation. 

"Conduction is the transfer of heat by direct contact with a cooler substrate. Convective heat loss occurs with water or air flowing over the skin and carrying heat away from the body. Evaporation is vaporization of water from a surface, as occurs when sweating. Radiation is infrared heat emission given off to the surrounding atmosphere. Heat loss depends on both the temperature gradient between the body and the environment and the amount of body surface area that is exposed. Under normal circumstances, the majority of heat is lost through radiation, but conductive and convective losses are generally key factors in the development of hypothermia." Evidence Based Medicine/Emergency Medicine Practice, January 2016

To try to reclaim and store heat, those same blood vessels that bring heated blood to the skin constrict to keep that warmth closer to the core. 

With adequate fuel (mostly carbs), and the ability to keep muscles moving, an active person can stay warm in very cold weather. I've been on the start line of cyclocross races thinking that I was turning into a White Walker, but by the end of the race I was dripping with sweat (yeah, even back of the pack fodder like me).

Problems arise when fuel runs out, our ability to keep muscles moving is impaired, our insulation is compromised (wet clothes), or temperatures drop. Maybe all of the above.

In the general population, those most at risk of developing hypothermia are the very old or very young, and people with certain medical or psychiatric conditions. But obviously anyone going outside on the trails on a cold day, who gets lost or injured or delayed--and is not prepared, is at risk.

Some of the first signs of hypothermia are called "the umbles." That's when someone starts to mumble, fumble, or stumble. I've seen grumble and crumble added to the list too. If clumsiness and complaining are starting to set in, it's really time to start packing it in. Shivering will be starting next, if it hasn't already, and that means your body is going into survival mode. Shivering will work to generate heat, but is very metabolically demanding, and as I mentioned, will really be dependent on having a good source of carbohydrates for energy.  Another, lesser known symptom that your body is becoming hypothermic is the need to urinate. Called "cold diuresis," when your body starts constricting peripheral blood vessels is bring more blood to your core, and more blood gets processed through the kidneys, and the kidneys can't keep up with their ability to concentrate the urine, so you end up with a large volume of diluted urine. 

Anyway, unless the person is taken out of the cold and started to be rewarmed, the situation can get more dire. 

In the next phase of "moderate hypothermia," the "umbles" progress to downright confusion, cognitive impairment, and lethargy. Trying to get someone out of the woods at this point is going to be very difficult if not impossible and warming in place might be the only option while you wait for rescue. 

With severe hypothermia, victims are typically comatose and will be very susceptible to fatal cardiac rhythm abnormalities, and really shouldn't be moved except by trained rescue personnel. Victims will be stiff, unresponsive, and have very slow respiratory rates and heart rates. This again is a situation where the person will need to be gently wrapped as best as possible, but left in place. 

Obviously, heading in to moderate to severe hypothermia, things can get bad fairly quickly, so it's best to be prepared and to let things get to that point. 

And remember, it may not take much--think of this--you're out riding, you do what you've been told, "start cold so you won't be too hot once you warm up," and after 20 or 30 minutes of riding, you've warmed up and feeling good when you break a chain or have some other mechanical. You spend 10 minutes or so trying to fix it, but you can't. You've started to cool down and the sweat you had generated is making you colder. You've got to walk out of the woods, and that 3 miles back to the car is going to take you an hour or more...

Maybe it's a broken snowshoe or a twisted ankle. 

Whatever. Shit happens.

“I thought they smelled bad on the outside!”  
Han Solo/Empire Strikes Back
I recommend, that in the cold weather, you bring a small space blanket (they're small, take up minimal space and really work to insulate someone), plenty of simple carbohydrates, and an extra layer. Jackets, vests and other outer shells pack small and can really make a difference. This is just for short hikes/runs/rides, if you're going to be out longer, or farther from a trail head, then more is better. An emergency shelter and a way to start a fire are good considerations.

Winter can be beautiful and fun, just take some precautions. And if you're thinking, "well, I can just warm up inside the belly of a dead tauntaun," that won't work, according to "science."

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