Originally Posted by
Kopsis
What the graph fails to consider is the physiological effect of having 20 lbs less fat (especially if riding in warm weather). So while it may not have much effect on how much power you need at the rear wheel to maintain a certain speed in the flats, the efficiency by which your body can produce that power may be increased. The effect will be an increased anaerobic threshold and consequently a greater reduction in fatigue than the 1% power difference might suggest.
I don't think it is, at least enough to make a meaningful difference. I could be way off on this, but here's how I understand it.
In a lot of other sports (think running) there's a lot of variation from one person to the next in what you're talking about, how efficient they are at turning stored energy (like fat) into mechanical work. But on a bike, we're all seated for most of the time, turning our feet in circles with our legs extended to about the same length as each other, etc. You might ride in the drops while someone else is on the hoods but it's pretty constrained and we all have pretty similar energy efficiency because of it. When you convert kJ from your power meter into kCals, you guess at how efficient you are at this, and there just isn't a very big range.