Abstract: A pedal actuated drive mechanism including two pedal structures to be actuated by the two feet of a user and preferably mounted to swing about an axis in two opposite directions, with the two pedals acting through a flexible cable or its equivalent to drive a bicycle wheel or other driven rotary unit through two one-way clutches each of which turns in a predetermined driving direction when a corresponding one of the pedals is pressed away from the user. Desirably the two cable lengths actuated by the two pedals respectively are interconnected for movement reversely with respect to one another, so that depression of the one pedal causes reverse movement of the other pedal. The effective power transmission ratio of the drive assembly can be varied by a controlled shifting of the points of connection of the flexible drive cable to the pedal structures to move those points of connection toward or away from the pivotal axes of the pedal structures, and thereby vary the effective lever arms of the pedal structures.