Originally Posted by
MadKaw
Strava said I burned 799 kCal on a recent ride.
Then Strava says I output 456 kjoules.
But if I remember my conversions, 1 kCal ~ 4.2 kjoules; I calculate ~3345 kjoules. Which would be an output ~ 670 watts.
I sincerely hope you divided by a time duration to conclude that...
What am I missing (other than my yellow jersey)?
One thing to consider would be efficiency. It's a basic rule of thumb that a person
just sitting there generates 100 watts of heat (or maybe a little less). Even before trying to do anything
useful. And obviously quite a bit more when exerting themselves, otherwise they wouldn't get all "hot and sweaty". That heat is the power wasted in inefficiency. Add to that whatever power you actually put into spinning the cranks.
Wikipedia seems to suggest that cycling muscles are 18-26% efficient. So assuming your earlier conversion was meaningful, take your 670 watts, let's subtract just 70 for overhead of staying alive. Then let's multiple the remaining 600 by 25% efficiency.
150 watts into the cranks.
Again, I have no idea if where you started from is accurate. But there will indeed be a huge difference between the food energy "burned" the and the useful mechanical work done at the cranks.