Heat and the limits of the human body
Nutters running in extreme heat
It’s so hot! 35℃ at 17:30 in the afternoon according to my phone. I love it! It’s my favorite time of the year. I love the heat.
I went running in the heat for half an hour or so yesterday and I’ll do the same today. Running in the heat makes me feel great. It seems to lower my blood pressure. Sweating out all that salt I guess.
Me and my son on the outskirts of Fez (Jbel zalagh is not shown, it’s to the left I think)
July 2018 I went to Fez in Morocco with my oldest son, just for an adventure. There is a little mountain just 5km away from Fez called Jbel zalagh, and I decided I wanted to run up it. My son— who is much more sensible than me — declined to join me.
I’m not sure what the temperature was but it was hot. According to this website it got up to 37℃ in July 2018. So I got a lot of water bottles in a backpack and started to run up the little mountain.
As I said, I like heat and I like running in the heat. But this time, when I was part way up the mountain, I started to feel a bit different and a little alarm bell went off in my head: “this is dumb and dangerous.” I can’t really describe the sensation but it was like I was just at some kind of limit where my body might not be able to cool itself faster than it was generating heat. I sat down for a bit, drank some water, and then walked back down the mountain. And I’m here to tell the tale. But the experience has always got me wondering — how much heat can the body take? What are the limits? Can you exercise to the point where your body cannot get rid of the heat fast enough through sweat? I’ve been doing a bit of research.
Our average body temperate is about 37℃. The body tries to keep the core temperature around that. To do that, the body brings hot blood to the surface of the skin, and generates sweat. So you loose a lot of water very quickly. I’ve got through about four liters of water on a couple of hours run in dry heat without urinating, which means I must have lost about two liters an hour through sweat (I just checked and this is reasonable for a man of my weight running). Apparently a) you can lose more water in sweat than your kidneys are able to create in urine and b) you can get hyponatremia (low blood sodium) if you drink too much water without salt. So that is something I should be aware of. As I mentioned, for me the sweating seems to lower my blood pressure, which feels good. But I guess I shouldn’t overdo it.
Humidity makes a huge difference. The body can’t get rid of heat through sweat if the air is already full of water. At extremely high humidity, sweating becomes ineffective — at a 100% humidity and 35 °C ambient temperature, sweat cannot evaporate at all, eventually leading to unchecked rise in core temperature, heatstroke, organ failure, and death! Is that level of humidity common? According to this site Kuala Lumpur, Jakarta, and Singapore have very high humidities year-round because of their proximity to the equator and water. Kuala Lumpur sees annual average humidity ranging from 74% to 86%. I guess it would be a bad idea to go running in the heat there. Note to self — don’t do that.
Heat stroke occurs when the core temperature of the body goes above ~40 °C. It can be caused if the body stops sweating due to dehydration. So drink lots of water in the heat. Everyone knows that. But apparently old people sometimes forgot or fall asleep in the heat or whatever and so die from the heat.
The body is made of lots of proteins and they start to fall apart and stop working (“denature”) over 40°C, which is no fun at all. ChatGPT wrote me a long research essay on the effect of heat on the body’s proteins and the bottom line is — stay under 40 °C. About 43 °C and above is extreme hyperthermia and “cells begin to die rapidly through necrosis due to protein coagulation and membrane failure”. You don’t want that. Let’s move on to something less horrific.
Apparently nutters and loonies do something called the Badwater Ultramarathon in Death Valley, California. They run 135 great USAian miles in temperatures that reach 50 °C in the shade. So it seems you can do a lot of running in extreme heat without killing yourself. My little runs are trivial in comparison. So I’ll continue running in the heat. But sensibly. It means I can eat lots of salty food without worrying about blood pressure — totally worth it!