EISPIRATEN

I guess this may be coming a couple months late but hey, somebody out there might appreciate this essay on getting out and about when temps are triple digit. There's some good info here and it's based on medicine and experience.

http://davidstillman.blogspot.com/2012/ ... -heat.html

Up to 25% of our water loss during high intensity cardio simply gets breathed away... [so] ...hike with your mouth shut.

Now, I did not know that. 25%! That is a lot.

Good information. A lot of the things you discuss (carry water, make use of shade, slow it down a bit, bring electrolytes, wear a hat, etc.), I was familiar with (and it's all right on), but I had not heard that hiking with one's mouth closed could help retain water.

Out of curiosity, how much water does one lose insensately when breathing through one's nose?

HJ

Jim, that's a question with no easy answer but to say that the losses are significant. I would suppose that it would have a lot to do with the relative humidity and the individual. In general the higher the body mass index (BMI), the higher the individual extracellular water weight, but that high BMI also suggests that the individual needs to pick a different day to hike because most of that excess water is stored in fat which of course, slows that individual down. I do know that hot and arid conditions suck the water out of you in ways that are difficult to quantify, but that awareness of those losses can lead one to adopt different hiking strategies. Good question, sorry I don't have a more scientific answer. -Stillman

Understood. Probably pretty hard to quantify without some testing, and it would take a lot of individual test cases before one could have confidence in a generally applicable rule. As an aside, it would also be interesting to see if water loss varied (and by how much) by fitness level, BMI, and degree of acclimation to hot/dry conditions.

Even absent hard numbers, hiking at a pace where one can have one's mouth closed and still comfortably hike means that one is moderating the amount of heat generated by exercise, and that alone should mitigate overheating. Add to that (presumably) lower rates of water loss, and I think we've got a good strategy, or at least as good as it gets when the mercury veers toward 100.

HJ

Jim, I like your thinking. Speaking of adapting to hot conditions, I can tell you that I required a lot less water when I lived in the desert than I do today. Clearly I was more fit and 10lbs leaner back then, but I am convinced that one can adapt, given time, to the quirks of most environments.

I've heard that Race Car Drivers prepare days in advance by hydrating their bodies in preparation for Race Day.
I guess it would be no different for hiking in the heat.
Talking from experience, I wish I knew this information before I tried hiking The East Fork during the summer. I Thought I was gonna pass out.

Pre-hydrating before a big event is really valuable. I've done it before my Grand Canyon hikes and always before a Whitney dayhike. Those are things I plan for, unfortunately the local treks are just wherever I feel like going on that particular day.

The worst I've ever had it is heat exhaustion on the hike out of Havasupai Falls in the Grand Canyon this year. I thought i was going to die.