[daveloyall]

I think your muscles are pretty energy efficient.

The kinetic potential battery (the weight lifted against gravity) is also very efficient.

Food is very energy dense. https://what-if.xkcd.com/128/ (sandwich vs battery)

Uh, change of topic: isn't the caloric value of a food how much heat can be released by burning it (probably when it is dehydrated)? Plenty of energy stored in a sandwich, sure. But a car battery could power a small spaceheater-like thing for... a while. There's a lot of potential for heat production in a car battery (even without BURNING it). Did Mr. Munroe get this one wrong?

[gus_massa]

From Wikipedia: https://en.wikipedia.org/wiki/Muscle#Efficiency

> The efficiency of human muscle has been measured (in the context of rowing and cycling) at 18% to 26%. The efficiency is defined as the ratio of mechanical work output to the total metabolic cost, as can be calculated from oxygen consumption.