Now replace the human with an animal and we're back to pre-industrial times - but this time, it's environmentally friendly, not necessary! Only half joking, be

Now replace the human with an animal and we're back to pre-industrial times - but this time, it's environmentally friendly, not necessary! Only half joking, because bulls and donkeys were used to power a lot of machinery and still are, and even dogs were used on hamster wheels to power rotisseries (their depictions were sad, indeed). But I would like, and have thought about, a treadmill or stationary bike to exercise and recharge a power bank or two, for example. It wouldn't be much, but it's not hard to implement and I'd rather have several smartphone charges than just excess motion/heat. On that note, it would probably be more efficient to grow crops, distill alcohol, quit drinking and use that to power a generator... That or compost it to gas, biofuel :D