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Fellow runner here. For God's sake man, carry an emergency blanket with you at least.

https://www.amazon.com/Emergency-Blanket/s?k=Emergency+Blank...

also a great make-shift Faraday cage for those pesky non-removable-battery phones

I don't know if that's true. In the nonideal world a Faraday cage must have a minimum thickness to function, which is a factor of the wavelengths you are trying to block and the conductivity of the material, I think.

Just the conductivity.

The article mentions that plastic bags work better than emergency "space" blankets since they block moisture and thus evaporative cooling. A large industrial trash bag is part of my emergency supplies on cold backpacking trips. It's cheap, weighs almost nothing, and provides protection from both radiative and convective cooling.

The article distinguishes it as a better option _when wet_

I'm surprised. I've lined up before races in the cold and I've found an emergency blanket keeps me warmer than a trash bag. I've tried both. Neither beats used sweats from Good Will, but that's too much to run with.

You're supposed to pretend your the garbage and climb into the bag - creating a closed system where you keep the lost water warm.

Related: I used ziploc bags as vapor barriers nested between two pairs of socks while on a multi-month winter hiking trip in trail shoes. It was extremely effective. I could posthole in deep snow all day in my running shoes and not get frostbite.

How did you avoid damp-related problems like fungal overgrowth?

It didn't end up being a problem. I washed my feet when I could, used thick wool socks, let my feet air out at camp, and that was enough.

Funny, this Californian ran a half marathon in northern norway rain (during the summer, though, so it was about 45f). I inadvertently tested this plastic bag theory.

My luggage had been lost by the airlines, so I didn't have my rain shell, just the most basic running clothes that I wisely chose to put in my carryon.

I ended up running the race in t-shirt and shorts covered by a free plastic poncho handed out by a restaurant. I quickly saturated my clothes from a combination of sweat and rain getting in, but it functioned like a wet suit in that it prevented the fresh rain and wind from cooling me evaporatively, while my body kept my wet clothes warm.

While it was a bit stuffy, I was afraid I'd get cold very quickly in the wind and rain if I took it off (which I did in the last few miles, and yes, it got cold quickly). As soon as I stopped running, even with a space blanket, even going indoors, my temperature plummeted EXTREMELY rapidly.

At 45f in the dry I'd typically use long sleeves (and I repeated this experiment this past weekend in Napa) although, again, it's really just to keep you warm while you wait to start; once you're running, it's no problem to get by with only short sleeves and shorts.

Space blankets are made of mylar, and are not porous.

Not sure why people here think that they don't block moisture and allow evaporative cooling...

https://en.wikipedia.org/wiki/Space_blanket

They're not a bag. Thus they're not sealable.

Long distance snow walkers (snowshoes/backcountry skis) will take the opposite approach. Oversized insulation + air permeable shell. Oversized clothing allows for complete ventilation when needed/possible. Air permeable shell allows vapor to escape or freeze onto interior surface and flake off under movement.

As for light/fast: I’ve worn a small running fanny pack with an emergency blanket and whistle at times.

I don't really understand this 'breathable' clothing from a physics perspective.

Every liter of water lost through breathable clothing is 2.3MJ of lost heat. So one would presumably prefer to have non-breathable clothing, keep that water in and potentially get 'clammy', yet stay warmer.

Yet nobody seems to do this. Is there a physics based reason other than 'it feels icky and is uncomfortable'?

Perhaps because even when in very cold environments there are occasions when the body is too hot and needs to loose heat?

Wet clothing is a life threatening situation in the backcountry.

Intentionally venting excess heat is common and not at all a concern for snow walkers.

Some cold weather gear works on that principle. Synthetic string vest for example, keeps you warm even when sweaty. It dries off quickly too when you are no longer sweaty. The main thing is that you are warm and never cold and that you shouldn't worry about soggy undergarment.

Would I be able to, say, sit down to do sit-ups and push-ups until I could warm up and resume hobbling.

It'd be tough. The muscles in your arms are much smaller than your legs. They produce less heat and induce less cardiovascular activity when working.

Try getting your heart rate up without using your legs. It's hard.

Hope you're not doing this someplace isolated.

Washington, DC, does have generally mild winters. The coldest I have been has been in cold rains, which are no fun to run in. One can almost always run in shorts, but below a certain temperature and with a wind blowing, you do need something windproof over or under your shorts.

> It does make me think, however, what would happen if I were to sprain an ankle or break a leg and be unable to run to generate heat.

This is a big fear of mine as well. If I'm going out of cell coverage, I always bring the 10 essentials and at least one extra layer. Even if my legs are cold, at least I'll have a fleece jacket.

While I'm happy for your health, I think running shirtless outside at 7 Celsius a bit risky, no? You may be able to sustain it for a while. But if any small accident happens (twisting the ankle for example) it's gonna get cold quickly.

I remember snowshoeing in the Colorado Rockies years ago. It was around -15, with strong wind blowing. But we were at high altitude and the sheer exertion of it was making me sweat after a while, so much that I actually unzipped my coat.

>>This last weekend it was 45 and blissfully sunny

Any temperature above 40 is pretty warm though, assuming you have a sweater and a jacket of course. Anything below that starts to feel cold.