The invention discloses a sport medicine or rehabilitation science hemiplegia body builder. The body builder comprises a support, a movable armrest, a rotating pedal, a seat and a foot massage device;the support comprises support rods fixed to the two sides of the bottom, multiple transversely arranged cross rods, a horizontally laid base plate fixedly supporting the seat and the foot massage device, a stand column supporting and fixing the rotating pedal and foot pads, the movable handle is fixed to the front of the hemiplegia body builder and comprises a connecting rod and a grab rail, therotating pedal comprises pedal bodies, double Z rotating shafts and a bearing pedestal fixed to the top of the stand column, the seat comprises a base, a cushion, a back cushion and a headrest, a strong spring is connected between the cushion and the back cushion, a movable moment arm is arranged on the outer side of the back cushion of the seat, and the movable moment arm comprises a power box, rotating shoulders symmetrically arranged on the two sides of the power box, a mechanical arm, a mechanical forearm and a holding rod; by means of the movable moment arm of the body builder, upper limbjoint exercise strengthening can be achieved for patients suffering from hemiplegia, the upper limb physical condition of the patients is greatly improved, and the rehabilitation speed is greatly increased.