It’s that time of year again (at least in the Northern hemisphere). For those who cannot say “me all face“, there are other things that let you go barefooted in colder weather.
[A repost.]
I’ve Got CIVD
No, it’s not some obscure sexual disease. It’s a human physiological response that allows us, in many cases, to go out barefoot for longer and in colder temperatures than we might have thought possible.
CIVD stands for “Cold-Induced Vasodilation”, and it describes what the body does when your extremities get cold. What happens is that, when exposed to cold, the body restricts blood flow to your extremities. However, if your body core temperature is maintained (that is, you are otherwise dressed warmly), your body, after a bit of time, will send extra blood to those extremities to warm them back up. It dilates (opens) the blood vessels, hence the term “vasodilation”. This automatic response is of course very important to the Inuit, who need to be able to, for instance, thread hooks for fishing in pretty extreme conditions.
It takes about 8-10 minutes for this warming to happen. The body then cycles this cooling/warming. After a while in the warm state, it will restrict the vessels again and your extremities will get cold again. My guess is that the body is testing to see if core body temperature really can be maintained. But then, after a bit, vasodilation occurs again, and the extremities warm up again. This cycle can happen a few times before a steady-state is arrived at.
This response can be conditioned. Practicing in the cold can speed up the vasodilation response. You can see that in this graph:
Onset of CIVD
from “Effect of chronic local cold exposure on finger temperature responses”. The control shows that, in unconditioned people, it can take 10 minutes for vasodilation to occur. However, for this particular person, training (or conditioning) reduced that to 2 minutes, and the (in this case) finger never got as cold as for the unconditioned control.
It turns out, however, that some people do respond better to conditioning that others. This graph shows pretty much the best-case scenario. Some people showed only a minimal response to conditioning.
So, how does this apply to barefooters? Well, it means that, in reasonably chilly temperatures, we may be able to do more than we think. If we are not conditioned, our feet may get cold before that magic 10 minutes and we may give up just before the body is about to rewarm them. By being aware of this physiological reaction, we may be able to take advantage of it to enjoy going barefooted longer.
One thing to keep in mind is that we must make sure we keep our core body temperature warm. There’s an old saying, “If you feet are cold, put on a hat.” It’s a myth that “ 40 to 45 percent of body heat” is lost through the head, but, as usual, even the debunkings need to be more carefully examined. Yes, if you are stark naked then no, you will not lose 40 to 45 percent of body heat through your head. But if you are well-bundled up, and only your head is uncovered, of course you will be losing most of your heat there. Adding a hat could tip the balance between being cold and being warm. So, once again, if you are barefooting in the cold, do make sure to bundle yourself up well. Members of the Society for Barefoot Living have found that ankle warmers do a nice job of helping keep blood warm all the way down to the ankle so that it can do a good job keeping the feet warm.
I was recently on a barefoot hike in which I was able to observe CIVD directly. The temperature was about 30° (-1C). There was about an inch of snow on the ground, but its thickness varied depending on which part of the trail I was walking on. Some of it had had enough other people walk on it to have removed the snow while other parts had the full one inch.
(Side note: walking in snow is often colder than just walking on cold ground. On cold ground, I have fairly thick soles that do a good job of insulating my feet from that cold. However, it seems that getting snow on top of my feet, and particularly on top of my toes, is what really chills them down quickly.)
My CIVD response seemed to take a while to kick in, even though my core body temperature was just fine, since my trails took me up and down some hills. At about the 6-minute mark my feet were definitely feeling cold. But at the 8-minute mark, the CIVD kicked in and my feet suddenly felt perfectly comfortable. By 26 minutes, though, they were feeling cold again (that’s the cycling). At 30 minutes they were toasty again, and they remained just fine for the next half hour they stayed that way, even when I was getting snow on top of them.
I did want to make sure that it wasn’t the case that my feet had gone numb, fooling me into thinking they were warm. To test that, I looked for a twig, shut my eyes, and then tried to feel for the twig with just my feet. I found it fine, and was able to pick it up with my toes. Good check.
Finally, another word of warning. Be aware of what you are doing, and do not stretch beyond your limits. If you foolishly go out in zero degree weather and wait 10 minutes for CIVD to kick in, you will have frozen your feet long before it has a chance to. Worse than that, if you damage your feet that way, you won’t be able to enjoy regular barefooting, and you’ll never be able to train your feet to enjoy cooler temperatures.
Also, in a comment to the previous entry, Barefoot Josh warned about cold and wet conditions. Even wet conditions alone can be a bit of a challenge, because your feet absorb the water and get soft. When soft, they don’t protect as well against much of anything. Adding cold on top of that (when your skin is less pliable) just aggravates things. Again, while limits can be pushed, don’t push so hard you fall off a cliff.
So, yeah, I’ve got CIVD. And so do you.
Ahcuah 
Just because I CAN do something, doesn’t automatically make it a great idea. If it isn’t comfotable and isn’t very enjoyable, then what’s the point? The original purpose is defeated and it becomes more about prooving a point. I’d rather just put on shoes.
But it is comfortable and it is enjoyable.
Do you also forgo ice cream because your throat gets cold for a moment?
(I would also add that even if it is slightly uncomfortable at times, that means that next time it’s not uncomfortable. Just like training for running. The first time, you huff and puff. After a while, though, your body has adapted.)
[Update: Let me add that I’m just fine with whatever you prefer. To each his own, and if you’ve determined for yourself that you prefer shoes in such a situation, fine. But for those who don’t mind stretching a bit, there is this other alternative.]
I agree with Bob that it can actually be a great pleasure to condition yourself for the cold. It’s a very individual thing though: It is enjoyable for some, less so for others. If you find it uncomfortable or even painful, get back into the warm.
For me the CIVD response works best when I am very active, so have a high amount of blood flow, as I am moving outside my heart is pumping faster which helps keeping the extremities warm. When I sit still for a long time I get cold nose, fingers, ears and toes even in a heated room.
You should also not forget heat conductivity. You get cold faster on wet ground. Water actually cools faster than snow.
It might also be psychological. When you’re not used to the cold, you will find the ground unpleasantly cold. That exactly same impression turns to “just cold, but not unpleasantly so” once you have carefully gotten yourself used to the cold.
I’ve felt the ground get colder each week since Aug. I have yet to really switch to shoes so it’s a given that there’s conditioning and “stretching” going on.
I went on a cold hike last weekend with huarches/socks, temp 30’s. Did the last half barefoot. Somewhat enjoyable. Still, there is less motivation to walk in general and it’s a far cry from warmer season conditions.
Mostly what I encounter now on a daily basis is cold, dark, damp concrete and asphalt. Tolerable to a point but not enjoyable. Much harsher than grass and leaves. Soon those concrete surfaces will be frozen and salted.
I also fail to see how a finger temp. chart has anything to do with bare feet, which are in constant contact with freezing surfaces. By dictionary definition, the bottom of the foot doesn’t “insulate” jack squat.
The skin surface is somewhat cooler than the blood, so it insulates a bit, which is why you don’t measure body temperature where you have thick skin. Still to avoid tissue damage the skin should always have a temperature above freezing. This article describes how coldness causes the body to react and warm up the cold body part, which works to some extent (in case of hypothermia the body cannot warm its extremities). There is a constant loss of heat energy through the feet and other exposed parts of the body but that’s necessary when we are active to get rid of the excess heat generated by muscles. When we stand still it’s a different story, the body generates a lot less heat that we must “radiate off” and the heart beats slower, generating less blood flow.
Let me just add that the stratum corneum on the sole is way thicker than elsewhere on the body. It is basically like having a layer of leather there. If leather-soled shoes insulate (and they do), so do thicker bare soles. The thickness provides a temperature gradient between the surface and the blood vessels. And it is easily tested: just put one ice cube on top of your foot (typical skin thickness of about 20 microns) and another under your heel (up to 2,000 microns). See which feels colder sooner.
You have all brought up some really interesting points. Speaking from experience, I have found that since I started going barefoot full-time, my feet do actually feel much warmer. When I wore shoes, my feet were always cold, especially in the winter. I would often have several layers of socks on. Once I got rid of the shoes, my feet warmed up nicely. Even now, in winter, my feet are comfortable and warm (except when I go walking outdoors, then the cold ground does tend to make them a little chilly). My only concern about being barefoot in winter is frostbite, but I am very careful and carry a pair of boots just in case an emergency arises and I have to be outdoors in bad weather for an extended period of time. I tell people it’s like having a pair of gloves. You don’t wear gloves all the time. You use them when you need them, just like any other tool.
[…] is still tricky hiking in these conditions. Even with CIVD kicking in, one’s feet can still get pretty cold just by walking on top of packed […]