Circular SUBs of course employ a circular motion like a bicycle but with crank arms generally shorter averaging 150mm creating a circular motion 300mm diameter. Using the stair analogy the rise and run of a circular SUB are the same 300mm / 11.8″.  Circular SUBs are sometimes described as bicycles without seats which is essentially what they are but with some important distinctions: Crank lengths are generally shorter than traditional bicycles to reduce the knee strain experienced when standing out of saddle on a traditional bike.  The frame geometry of a SUB is specialized to accommodate the stand-up and ride posture.  Some circular SUBs provide an extended wheelbase to enhance the safety of a stand-up-bike which is an important consideration since SUBs have a higher center of gravity than a traditional bicycle.  Other circular SUBs are very compact to enhance portability.  Circular SUBs have pedals/platforms supported by a spindle like a traditional bicycle.  Some have large platforms which can help support your foot however these platforms still pivot about the pedal axle providing a single point to transmit power. A larger platform will transmit power through the arch of the foot. Some prefer a traditional pedal permitting traditional bicycle pedal motion with power transmitted through the ball of foot. The traditional pedal will be more powerful engaging more muscles but also more taxing upon those same muscles.  Examples of Circular SUBs include ElliptiGO SUB, Halfbike, Stike.