Position on pedals and more. Position on pedals and more.
Foot position is quite different on a bicycle than it is a uni.
On my uni I position the center of my foot on the pedals, while on my road bike I position the ball of my foot on the pedal's centerline of the axel. I also find that I work different muscle groups when I ride the uni, maybe because of the shorter cranks and being more upright. The worst case, as in mine to learn to ride a uni, is a bicyclist who rides a lot with no hands.