The whole secret to CIVD is getting sufficiently warm blood down to your feet.
How warm? And how can you do so?
First of all, just going barefoot helps with blood flow. Sometimes it seems as if shoes are designed specifically to impede the feet in everything. In a standard rigid shoe, the foot is encased so that none (okay, few) of the muscles actually do anything, and thereby cannot generate any heat of their own. In addition, in order to prevent blisters, shoes are usually laced up tight. That puts pressure on the veins trying to return blood to the heart, which reduces blood flow both returning the cooler blood and any warmer blood trying to get down to the foot.
If you do wear something on your feet, you want it to be as loose and unrestrictive as possible. For temperatures below my comfort-level, I will wear full-leather moccasins or mukluks. That is, they don’t have a hard sole—nothing but pliable leather. In Dual Survival, Cody Lundin will add wool socks to provide insulation. Again, these provide that insulation without restricting blood flow to the feet.
But there’s another way, as illustrated in this article, Canada wins the war on frozen fingers. Researchers at their Department of Defence (for some reason they spell it funny, :-)) found out that a heated vest, complete with thermostat, could keep the extremities, right down to the toes, warm. This was warm enough to actually clean a rifle, which takes quite a bit of finger dexterity.
All it had to do was monitor the fingers’ temperature, and if they started getting too cold, up the heat to the body itself. In an effort to cool off, the body sends warm blood to the extremities. What is amazing is that this actually works.
The report on the research is in Maintaining Finger Dexterity in the Cold: A Comparison of Passive, Direct and Indirect Hand Heating Methods.
They compared four different methods at -15°F (-25°C), with a slight wind: various gloves (“passive”), specially-heated gloves (“direct”), light gloves with the special vest (“indirect-passive”) and no gloves but with the special vest (“indirect-bare”). The special vest won, even over heated gloves (which, while they supplied sufficient heat to keep the fingers comfortable, lessened dexterity).
Here’s one of their graphs.
The first thing you notice is the Cold-Induced Vasodilation. But even though it was cycling, the finger temperature never dropped below 24°C, and the hands and fingers stayed comfortable. The “passive” solution was just downright uncomfortable.
Toe temperatures were also kept comfortable with the special vest on, even while dropping with passive insulation. (For some reason, their data plot does not show CIVD at the toes.)
OK, so what does that mean for those of us who go barefoot in the cold without one of these special vests?
Well, it shows the importance of keeping the core temperature raised. If we prepare properly, we can handle much cooler temperatures than we think (though I have my doubts about -25°C; I’ve never maintained decent comfort below about -2°C).
But here are some tips.
First of all, keep in mind the sage words from the old classic, Dem Bones.
The toe bone’s connected to the foot bone,
The foot bone’s connected to the ankle bone,
The ankle bone’s connected to the leg bone,
The leg bone’s connected to the knee bone,
The knee bone’s connected to the thigh bone,
The thigh bone’s connected to the hip bone.
You want to maintain insulation all the way from the foot to your torso. There is no point in keeping your core warm if the blood cools too much before it makes it to your feet. Overdress your legs in addition to your core.
Exercise of course warms you up. On my last Adventure Hike at Clear Creek, we did about half a mile on level ground at 30°F. My feet were definitely cooling during that 10 minutes. And then we hit a hill. My feet warmed appreciably on the way up, and stayed comfortable from that point on (it also didn’t hurt that the temperature was slowing rising during the day).
Don’t drink cool liquids. That’ll just cool down your core temperature, and it’ll do it a lot more than you think. (After all, that’s why we drink cool liquids on a hot summer day.)
Be aware that there is a difference between the hands and the feet. The hands are touching only air, while your feet are touching the ground, which can convey the cold a lot better than the air. Runners have an advantage here, since their feet are off the ground a bit more than they are for hikers or walkers. Keeping your feet warm also depends on how much insulation you have on the bottom of your feet—thicker soles mean more insulation.
I’ve also mentioned this before, but I don’t have much trouble walking on top of cold snow, but if I get it on top of my toes, that cools my feet down really quickly. There’s just no insulation on the tops of my feet. (Of course, a hobbit wouldn’t have that problem!)
One more thing: be careful about sweating. You need to stay warm without over-sweating. If you sweat and stop, the sweat will cool down your core very quickly.
And yet another thing: you really need to monitor your feet. You don’t want to ruin them by overdoing it. You should regularly test them by using them to feel something like a log. You should be able to feel the texture of the log. If not, take action. (And this time of year you should always have backup footwear of some sort along.)
Anyways, it really is possible to be out in the cold and continue to experience the joys of barefooting. Give it a shot!
Totally what i have experienced a couple of years ago, last winters in the Netherlands have passed allmost whithout freezing, I love running barefoot in snow. I have managed to keep my feet comfortably warm to about -6 C . -25 is something completely different, but freezing periods in the Netherlands are generally short lived, especially nowadays, so I have very little experience with colder temperatures, beware of salty slush!!