Sometimes when it's hot, I stick my leg out from under the covers and it's like an instant
cooling effect.
But when it's cold, I want socks to keep my footsies warm!
Why do the feet have so much thermal power!?
If you're watching this, you are warm-blooded.
Unless you're an alien, or a reptile that's learned to understand human speech…
If so… then, um.
Hello.
Warm-blooded animals have thermoregulation -- we're constantly burning energy to keep
our internal organs at optimal body temperature[a].
Temperature is maintained by the burning of energy, but ALSO sweating, shivering, and
overall skin blood flow, and our feet and hands' major weapons in maintaining temperature.
Normally, blood runs from the heart, through arteries, vessels, capillaries, to cells and
then back through veins to the heart.
When it's hot, things open up and blood flows more freely; and the opposite happens when
it's cold.
The thing is, not all parts of the body are treated equally by the brain.
In the 1930s, the cortical homunculus was created to describe how our brains see our
bodies.
Limbs aren't that important, and thus input is largely ignored by the conscious mind;
but, hands, lips, genitals and so on are REALLY important!This model vogues with thermoregulation
in some respects as well.
Our feet, for example, are often ignored… but are really important for thermoregulation!
When you feel uncomfortably cold, the somatosensory cortex of your brain triggers to start thermoregulation
-- to up your body temperature by shivering, or opening blood vessels.
Inside the feet are arteriovenous anastomoses, which connect arteries directly to the veins,
bypassing the capillaries.
When you're warm, vessels in your feet dilate allowing more blood to get to the skin -- regulating
your temperature -- cooling you down.
But, when you're cold, those arteriovenous anastomoses restrict, forcing more warm blood
into the surface, which lets heat escape, cooling you off.
This is why you put one foot out from under the covers.
According to a spokesperson for the National Sleep Foundation,
when you stick your foot out, the arteriovenous anastomoses allow the foot to cool you off,
regulating your body temperature without disrupting your overall comfort.
Biology aside, thermoregulation also has to do with comfort.
Mom used to say most of your body heat was lost through your head and feet.
But it's a myth, sorry Mom.
It probably originated from the 1970 U.S. Army Survival Manual, where they said "40
to 45 percent of body heat" is lost through the head.
Because the brain focuses on the head and chest for thermal comfort rather than the
appendages and your feet chances are they were more concerned with the comfort of their
soldiers; not the actual core temperature.
In reality, a 2008 study in the British Medical Journal found heat loss is spread pretty evenly
across the body, with only about seven to ten percent being lost through the head.
According to a 2009 paper from the University of Wollongong most of that discomfort centers
on the heat levels in our[e] head, hands and face.
Perhaps because of that brain perception problem.
Our poor downtrodden feet just get left in the dust.
Our feet can be colder than our hands, head or chest, without affecting our conscious
discomfort levels.
Thus it is the perfect candidate to thermal regulate while asleep.
Long story short, feet can be a bit cold and you'll still be snug as a bug in a rug.
What kind of crazy things do you do to get to sleep?
Maybe we'll do a video about how that works…