I puzzled over this until I realised that the picture you have of me (and possibly of Stumpi, too) is of a body sitting on the saddle pedalling with one leg while the other pedal goes around freely on its own.as you stop putting pressure on the pedals the power stops so would be completely useless for someone with one leg.
Not so. Should have been clearer: one REAL leg. Plus one plastic/metal combination. With which I pedal. Not quite so efficiently as with the real one, of course, since the absence of a calf muscle slows things down, but I can still bring my body weight to bear and unlike many amps (above knee) I still have my thigh muscles in reasonably good working order.
I shall post pics of me on bike with which you can scare the horses.
Allen