Wednesday, July 17, 2013


Last week, I got on the subject of body temperature with a colleague. He mentioned he had one of the newer style thermometers that you swipe across your forehead, like hospitals use now. I hadn't seen one, so he brought it in for me to check out the next day.

Pretty nifty. Fast and non-invasive. It uses an infrared sensor to measure the blood temperature in your temporal artery, which comes straight from your heart and goes across part of your forehead. The new thermometers are claimed to be very accurate at measuring core body temperature. They only cost $30-35, so I picked one up at Walmart on my way home. While we could use an updated body thermometer in the house, my real intention was to measure my core body temp in this hot weather while working out on the bike. The unit slips nicely in a jersey pocket and doesn't weight much.

That evening, Cathy and I played with it a bit. Cathy was consistently under 98F, while I was consistently over 99F. This was in an air conditioned house and after supper.  I always get warm after eating. A 2F difference in our body temps is indicative of differences in metabolisms. I find in the morning I'm more normal, low 98's.

So yesterday I took the Exergen with me on my intervals ride at lunch time. It was oppressively hot. I expected full thermal slowdown, maybe 103F or even 104F body temperature. I did get this high once in a controlled heat stress study I participated in at UNH. Only took me 20 minutes into the time-trial to get that warm in a low-humidity, two giant fans blowing on me, 95F room.

After my second, fairly long interval Wednesday, I stopped at the summit of Jeremy Hill to check my body temp. It was 97F. Huh? Check again and again. No more than a couple tenths of a degree variation. WTF. I was totally overheating. I did two more intervals and took another quick scan. Same thing. How can I be 2+ degrees hotter at rest in AC than doing 400W intervals in 94F heat? Something wasn't passing the goofy test here.

So that evening I started to dig a little into this. I found exactly what I was looking for in this piece of work.  Turns out temporal scanners don't work well at all when exercising outside. They measure ambient temperature and make certain assumptions about how much heat is being gained or lost through the skin. These assumptions break down when exercising outside. The study clearly showed temporal scanners under-measured core body temperature by a lot compared to an rectal thermometer. I'm not about to go there.

So I didn't buy it for nothing. It is very accurate when not exercising indoors, more accurate than oral, ear or forehead strips. So it will be good to have on hand.

Doing most of my riding midday this summer, I'm quite certain I'm the most acclimated to riding in heat than I have ever been. There's no way to avoid it. I rode again today at noon. The hardest part wasn't pushing the pace a bit half way into the ride. No, the hardest part was walking out of the office into a blast furnace. It seems this summer my body has learned to turn on its "AC" system quickly when going out into the heat. Once it turns on, it doesn't feel so oppressive.

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