Comment by matthewmcg

It's no coincidence that other human-powered transport mechanisms (aircraft, boats, etc.) commonly use pedals for the drivetrain. It's a lightweight way to use the body's strongest muscles, especially when high power is critical.

See:

https://en.wikipedia.org/wiki/MacCready_Gossamer_Condor https://en.wikipedia.org/wiki/MacCready_Gossamer_Albatross https://en.wikipedia.org/wiki/MIT_Daedalus https://en.wikipedia.org/wiki/AeroVelo_Atlas https://en.wikipedia.org/wiki/Hydrocycle