How Heat Affects Heart Rate, Or At Least Mine

Filed under “Experiments With Bodily Functions”

I’ve been riding the spin bike a lot lately. I had some self-induced mechanical issues with my TT bike for a while. And it was hot. And I usually don’t get a chance to ride until after 10 pm anyway. So it’s been really convenient. But I’ve noticed that I have a really hard time getting my heart rate up on the spin bike. I’ve done some interval workout videos where the folks on the video are working in the mid to high 160s, while I’m at a perceived effort level of 4/5 and not getting over 140. And the averages for these rides are always in the 120s. I know what pushing feels like, and I “feel” like that’s what I’m doing, but the HRM doesn’t show this work I’m feeling. And when I’m just spinning at a perceived level of 1/5, I’m lucky to break 110.

Yesterday I went out on my TT bike for the first time in a looong time. Weird, but no problem getting my heart rate up there. I was sustaining ~160 on 3 minute intervals, and averaged 144 for the 20 mile ride. During the cool down portion of the ride, my heart rate was ~133, and that was with a perceived effort level of 1. I could have sung opera (if I could sing).

The one major difference between riding the spin bike inside and riding a real bike outside is temperature and humidity. With the spin bike, I ‘m sitting directly beneath an air conditioning vent and a ceiling fan. But still, riding in a cool and humidity-free environment couldn’t have that much effect. Or could it?

I must employ the scientific method to find out for sure–had to collect some data.

During lunch today, I put on my my HRM and sat in the floor, leaning against the sofa for one minute. I then started a split and collected HR for one minute, and got an average rate of 52.

Then I went out to the driveway and sat down, leaning against the car. I waited for 5 minutes…just long enough that my feet were no longer cool and I felt like I was about to start sweating. Another minute with my HRM, and I got an average rate of 67.

So it takes me 15 more beats per minute to do nothing in the heat than it does to do nothing in the cool! And it was only in the mid-80s today!

One thing I’m not exactly sure about is how I can accurately extrapolate that data based on temperature though. Do I use a constant change of ~15 bpm when comparing hot weather workouts to cold weather workouts, or do I use a percentage (30%?!?!) difference. I’m leaning towards the first option, but I probably need to collect more data.

That means more spin bike. Outside. In the heat.

Torture.

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