Alternate title: Why the human body is so amazing, and Erika is a science nerd.
I was thinking about this during my entire 4000 meters swimming this morning. Maybe that’s a sign I’m in academic withdrawal? Luckily, I found out yesterday that I was ACCEPTED to my grad program of choice, and have another three years of debt education ahead of me. In the mean time, I feel it 97% necessary that I share this with you. Consider this your Thursday science lesson!
During exercise, the hypothalamus (see pencil point, above) detects core temperature, and then sets off a series of reactions to regulate (either generate or dissipate) heat. The body is pretty much a pro at this, keeping core temperature at 37°C ± 1°C. When exercising in the cold, the posterior hypothalamus may sense a change in skin or core temperature and begin several reactions in order to generate heat (and avoid hypothermia):
Shivering: Involuntary muscle contractions -> can increase heat production by up to 5 fold. However, it can also impair performance and decrease muscle coordination.
Non-shivering thermogenesis: Epinephrine and norepinephrine are released by the sympathetic nervous system -> anaerobic glycolysis and release of free fatty acids. Happens to a greater extent in children due to their greater percentages of brown fat.
+ Thyroxin production: thyrotropin-releasing hormone increases -> release of thyroid stimulating hormone increases -> increased thyroxin production -> increased metabolic rate.
Vasoconstriction: Sympathetic nervous system signals smooth muscles to constrict -> shunts blood away from skin and into deep tissues to maintain core temperature.
The body does of all of this BY ITSELF! You don’t have to sit there, mid-run, telling yourself aright homie, HTFU and shiver!! It already knows what to do, and is doin’ it without you even thinking. That’s not to say you’re 100% home free to go streaking during the next snow storm though. Three main points to keep in mind:
Hypothermia. Many athletes, and especially those in their first winter attempting outdoor exercise, tend to overdress. Overdressing can lead to hypothermia when you accumulate sweat, and then are unable to evaporate it, decreasing the body’s ability to sufficiently maintain heat. Warning signs of hypothermia include: constant shivering, or if the body suddenly stops shivering, muscles becoming weak and stiff, feelings of elation or intoxication (stumbling, slurred speech, poor decision making), and finally loss of consciousness. Don’t let hypothermia happen to you. Choose moisture wicking materials!
Frost bite. 82°F sounds warm, right? But when skin temperature reaches 82°, it begins to tingle. When it hits 68°, it starts to hurt. At 50° it goes numb. And when the skin temperature reaches 27°, it freezes. Enter frostbite. Obviously skin temperature and air temperature are two very different things, because exposed skin won’t go numb when it’s 50° outside. According to one winter runner in this NY Times article, when she stopped and took off a glove to feel how cold her ears were mid-run, they felt like “frozen meat.” It can take months to determine the damage frostbite has done, and some skin may never regain normal sensitivity. Don’t let frozen meat frost bite happen to you. Cover exposed skin, and take head of this handy dandy chart:
Stupidity. Feeling hard-core, or like a bamf, can be an intoxicating and persuasive emotion. It can lead us – you, me, your little brother, grandpa in his ice house, the newbie “winter warrior”, no one is immune – to make stupid decisions. Sometimes when it’s raining ice at a horizontal 27 mph, -3°, 6pm and dark, we get the idea that a quick loop of Harriet and Calhoun with our running buddies would be “fun”. The risk is not in that it’s “too cold” .. but that the conditions may prove dangerous and place you in situations out of your control. Your Yak Trax might do the job just fine, but that doesn’t ensure that Toyota Corolla’s tires will stop at the stop sign. You may be dressed warm enough for -50°, but that doesn’t ensure you wont bust your !!! on the hill on Williams Barry Pkwy. Don’t let stupidity happen to you! Common sense goes a long way.
Well, the bell’s about to ring. Which means… RECESS! Get out and play. 
-E
Thanks, Erika! This is excellent material ready-made for practical use. I would hate for my meat to get frozen!