[allendoerfer]

You should have posted that at the top level, so this could be the top comment. While the statistics are nice to look at, I have read the article you mentioned, too (was on HN a while ago) and instantly thought that metabolism unfortunately renders the whole calculation useless and wrong.

[thaumasiotes]

> While the statistics are nice to look at, I have read the article you mentioned, too (was on HN a while ago) and instantly thought that metabolism unfortunately renders the whole calculation useless and wrong.

Why did you think this? Can you articulate a change that metabolism would make to the calculation?

[allendoerfer]

It adapts, like my parent comment has said. Most of our energy is spend on keeping the system running, not running with our feet. If we start to run, we burn more energy, because our metabolism has not adapted yet, once it adapts (see his example with Africa), there is very little change. Obviously this is simplified.

[thaumasiotes]

Are you claiming that running requires no more energy than sitting? If not, what are you trying to say?

The energy that you need to spend on overhead doesn't go down because you start running.

[allendoerfer]

I am claiming that there is no linear relationship between the amount of running and burned calories.

[thaumasiotes]

So what? If you propose to have someone do some amount of running that they wouldn't otherwise have done, they must pay for that running in one of two ways:

1: Eat more. This has a linear relationship to the amount of additional running.

2: Do less. By doing less, you can redirect calories that would have been burned anyway to the task of running. You cannot, by definition, redirect calories that are budgeted for the basal metabolic rate.

By paying for the extra running "in kind", by not doing activities you would otherwise have done, it is easy to show a nonlinear relationship between "total running done" and "total calories expended". But that's spurious, it has nothing to do with the energy cost of running. There is a linear relationship between "total running done" and "total calories expended on running", and that is what matters when calculating the cost of running.

[allendoerfer]

Unless one does this every day, the metabolism adapts and one now does not need to eat more (or significantly less "more").

The correlation is not that simple as you make it sound.

Edit: To anticipate your next answer: If you run more on top of that, yes, you have to add additional calories somehow and the process starts again. The point is that a car does not have this mechanism at all so it does not make that much sense to compare them like equals.