Speaking of Efficiency

I read today, in an article about heat illness in runners, that human muscles are actually shockingly inefficient. Evidently, 75% of the energy used by your muscles goes to producing heat, leaving only 25% for accomplishing whatever task you are supposed to be working on (mixing concrete by hand for deck footings, say, or riding your bike to a foreign land like Michigan.) Maybe I am stupid after all, advocating for human powered transport. Oh well, I've done lots of things more stupid than that.