40F with or without clothes? 4-6 hours without clothes and Im pretty sure you're looking at fairly severe hypothermia.

In 40F water for 4-6 hours and you're looking at a severe case of death.

and even a mild case of death can kill you...be careful out there!

40F outdoors with clothes.

Ice baths are several minutes.

The faster the thermotransfer, the shorter the cold shock period, obviously...

I figured that was air, like "cryo". Later:

similar effects for immersion in cold water for several minutes as well

No kidding. Must mean 4-6 minutes.

IIRC the scenario was with clothing on where people spend extended period of time outdoors in the cold. E.g. shoveling snow, hiking on a cold day, etc.

Activity makes a big difference. Sitting outdoors for 4-6 hours without a coat in 40F would mean hypothermia for most people. Heck, I lose peripheral circulation and get sick more easily after sitting outdoors for just an hour or two in 50F WITH a coat if it's not an adequate one.

I am not sure how much clothes would help in preventing hypothermia.

Generally, quite a lot, as long as you stay dry. I spent 8 straight hours outside shooting pictures while standing - and occasionally lying down - on a frozen lake in northern Canada in January. It was -25C / -13F. I was perfectly comfortable, although I did have to repeatedly switch batteries with ones that I'd been keeping inside my coat.

Goal was to get pictures like this: https://goo.gl/images/imXCMy

(Those are methane bubbles frozen in the ice.)

"It's not the [lack of] heat, it's the humidity" applies in the cold, too :)

It's occasionally getting to -20-25 C during winters where I live, but people go around in their daily routines (only exception is children that do not have to go to school if it's below -20 C). I'm pretty sure if not the clothes, there would be a hell lots of frozen bodies around every winter.

Clothes are the reason people don't regularly die when they go skiing, or for that matter, live outside the tropics.

Would you mind linking to an academic study concerning the mitochondrial biogenesis effect?

These videos reference some studies on brown fat: https://nutritionfacts.org/video/brown-fat-losing-weight-thr... https://nutritionfacts.org/video/boosting-brown-fat-through-...

First hit on google: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5545200/ The effects of exercise and cold exposure on mitochondrial biogenesis in skeletal muscle and white adipose tissue

Seems like you need cold and exercise, at least in mice to get the effect in fat.

No idea.

Just passing along the info. At about the halfway period of the aforementioned video she has of her talk at a conference, she goes over the biogenesis effect, but I dont recall there being a direct study link. But in other videos, she does show screen shots of the studies when she makes statistical claims which make the studies pretty easily searchable on pubmed.

Her published stuff on foundmyfitness.com does have studies though.