Sitting in a frozen lake or climbing the snowy peak of Mount Kilimanjaro with nothing but shorts and trainers on does not sound like a recipe for good health.
But caves didn't come with air conditioning, and investigative journalist and anthropologist Scott Carney says our bodies are designed to experience extreme environmental conditions.
In his book, What Doesn't Kill Us: How Freezing Water, Extreme Altitude, and Environmental Conditioning Will Renew Our Lost Evolutionary Strength, he argues for adding environmental stimulation to your fitness regime.
He told Afternoons with Jesse Mulligan that most people in this air-conditioned age are cocooned in a constant temperature of about 22°C but our ancestors struggled against the environment. And these stresses are very important for our health.
“We have a whole hidden biology that allows us to adapt to a dazzling array of conditions.”
Carney says for a long time the dominant narrative has been that human health rests on the two pillars of diet and exercise, but his research shows that the third pillar is environmental.
For example, an upshot of being very cold is that it triggers vasoconstriction – the narrowing of blood vessels – which exercises your cardiovascular system.
But a more tangible benefit is that you lose weight really fast in the cold, Carney says.
When he first encountered the theory he was deeply sceptical.
Dutch fitness guru Wim Hof, also known as the Ice Man, is a high profile proponent of the extreme feats people can do in the cold, and when Carney went to meet him it was to debunk these claims.
“But the fact is that in the matter of a week I went from a guy living in Los Angeles, in this perpetual beautiful summer, to being able to stand out in [my] shorts in this Polish winter, and climb up mountains in Poland where the temperature dipped to 2 ℉ (-16°C) … and I was sweating the whole time.
“Our bodies are so attuned to climatic changes. We have billions of years of evolving that has happened to get us to where we are right now, and the organisms that passed on their genes were the ones who were able to adapt quickly.”
Carney says rolling around in the snow, or jumping in very cold water triggers a tensing in the body which is part of the fight or flight response.
What you are aiming to do is relax into this feeling, which makes your body stronger and increase endurance, he says.
“And [what’s] amazing is it’s pretty easy to do.”
And if you can’t make it to the Polish mountains, a humble cold shower will also work.
“The most immediate thing is that you will get this high," Carney says.
“Because once you have poured that cold water on you you will release norepinephrine, epinephrine, adrenaline, cortisol, all these feel-good hormones, and you’ll get out of it and you will feel awesome.
“You will feel more awake, you will feel more alert and that is just because you are triggering this unconscious biology.”