Showerthought: what’s the simplest way to tell that the human body is less than 50% efficient at converting chemical energy to mechanical work via running? I think it’s that running uphill makes you warmer than running downhill at the same speed.
When running up a hill at mechanical power p and efficiency f, you have to exert p/f total power and so p(1/f − 1) is dissipated as heat. When running down the hill you convert p to heat. p(1/f − 1) > p implies that f > 0.5.
Maybe this story is wrong somehow. I’m pretty sure your body has no way of recovering your potential energy on the way down; I’d expect most of the waste heat to go in your joints and muscles but maybe some of it goes into your shoes.
Showerthought: what’s the simplest way to tell that the human body is less than 50% efficient at converting chemical energy to mechanical work via running? I think it’s that running uphill makes you warmer than running downhill at the same speed.
When running up a hill at mechanical power p and efficiency f, you have to exert p/f total power and so p(1/f − 1) is dissipated as heat. When running down the hill you convert p to heat. p(1/f − 1) > p implies that f > 0.5.
Maybe this story is wrong somehow. I’m pretty sure your body has no way of recovering your potential energy on the way down; I’d expect most of the waste heat to go in your joints and muscles but maybe some of it goes into your shoes.
Running barefoot will produce the same observations, right? So any waste heat going into your shoes is probably a small amount.