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An athlete will only generate ~200w which isn't a lot for a fairly large metal part with plenty of air cooling. Even if it was only 50% efficient you might struggle to notice an appreciable change in temperature.

Motorcycles can have 150hp engines (~100kw) and even then the chain doesn't get particularly hot.

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I might be a bike fanatic, but I'm no professional athlete and I can sustain more than 200W for hours, so my guess is the pro's are quite a bit higher again. (Your point still stands, though)

You are right, serves me right for going by memory. 200w is closer to an average cyclist, a pro is closer to 500w. Still, the orders of magnitude don't change.

During a sprint in 2018, Andre Greipel averaged 1,600W, and hit 1,900W peak. Those are the kind of numbers engineers have to take into consideration when designing for maximum torque, although obviously they are not sustained for hours.

Wait, you're saying 1 human = 2.5 horses?

Fun fact. Peak horse power for a horse is 14.9hp :)

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