Join Date: Mar 2006
Location: Vancouver, Canada
Bikes: Rodriguez Shiftless street fixie with S&S couplers, Kuwahara tandem, Trek carbon, Dolan track
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I would suspect this has to do with efficiency.
Coming from a racing background, I'm used to seeing cyclists who are really slim and fit and who eat a lot. When I tapered down my racing and started doing recreational rides on the tandem, I tended to see more of cyclists who were a bit plump and overweight, but who could still ride the distances at good speeds, and who ate a lot.
So I've come to this theory that at some point, if you are not doing hard race-oriented training (like intervals and hill repeats where you are going anaerobic and experiencing muscles burning), your body becomes really efficient at spinning along aerobically, even at reasonably high speeds (not at threshold, but comfortably below). And I mean REALLY efficient, to the point that you are not burning as many calories as you used to have to burn. But, being used to eating a lot, these overweight recreational guys continue to consume the amounts they think are the entitlement of this "usual" amount of exercise.
So when you change your mode of cycling, by either going harder, or even by going much easier (which requires maybe different muscles, or muscles firing in different sequences, or weight transferred differently), the body becomes less efficient, and you appear to be burning more calories.
That's my theory, anyway. And my anecdotal evidence is that I'm 6'1" and 170-175 lbs, and I've done century rides (in miles) in cool weather on a fixed gear bike on less than one bottle and a few pieces of fruit, with no problems. I don't remembe rthe last time I've bonked, and I'm not sure I could bonk if I wanted to. The body is just too efficient... And I can't do slow rides, too frustrating, but I just thought that was the Type A in me.