Fat Burning Zone

Nice ride this evening. The temperature was--get this--80˚ on April 2. No, I haven't moved to Alabama. This is still Michigan.

So I was in my überunmodish hi-viz yellow t-shirt and Riv biking shorts (and, of course, New Balance walking shoes joined only informally to the pedals). On the Rambouillet.

But I got to thinking about Grant Petersen's latest post about fat-burning heart rate vs. muscle-burning heart rate (always go below 70% of your maximum heart rate to burn fat rather than muscle), and I thought I'd give it a try: never go above, say, 115 bpm. It was very pleasant. Very slow, but pleasant, and well in keeping with my resolve to go slow. But then I got to thinking: This is nuts. There's no way toddling along at 14 mph burns more fat than blasting along at 18 mph. It's impossible. Calories are calories, and 18 mph burns more.

Maybe it's just an April Fool's joke. But I reread the post, and it's not that funny. Perhaps if he had said that it's better to lie on the couch watching Wheel of Fortune than ride a bike, then it would be obvious. But this was no obvious joke.

So I looked it up here and there. Most confirm the obvious: When you're working harder, your heart is beating faster, and you're burning more calories. No one suggests that those calories are coming from muscles rather than fat, as Grant suggests. Burning more calories is burning more calories. Otherwise, walkers would be fitter than marathon runners.

This isn't going to inspire me to try to average 18 mph all the time, but it might cause me to reset the odometer so that I can track average speed, in general, as a point of reference. When I'm riding 100 miles, I don't want to average more than 15 mph. When I'm riding 20 miles, as I did today, I should average about 16 mph. And when I'm out for a quick little 15 miler, 18 mph is not unreasonable. (I'm old, so 18 mph is pretty fast.)