An exerpt from the article “The short history of early pedal powered machines” by Kris De Decker, published in Low-tech Magazine:
No matter how simple it seems to us today, pedal power could not have appeared earlier in history. Pedals and cranks are products of the industrial revolution, made possible by the combination of cheap steel (itself a product of fossil fuels) and mass production techniques, resulting in strong yet compact sprockets, chains, ball bearings and other metal parts.
Prior to that time, the available materials were not strong enough to take the large force that was acted upon them. This is even truer for stationary pedal power than for road bicycles, because the strain on parts is considerably larger. Experiments in the 1970s designing pedals, cranks and bearings for stationary pedal power units using pre-industrial materials like wood failed. And while the frame of a pedal powered machine can be made of wood or bamboo, steel is a better option – contrary to road bicycles, a lightweight frame is not an advantage for a stationary machine.
It is important to realise that pedal powered machines (and bicycles) require fossil fuels. If we burn up all fossil fuels driving cars, we won’t be able to revert to bicycles, we will have to walk. If we burn up all fossil fuels making electricity to drive our appliances, we won’t be able to revert to pedal powered machines, but to the drudgery that went before them.