The exercise tool consists of a frame that includes a base (14) that supports the machine main body on a horizontal surface. A seat assembly (12) with a support unit is fixed to the frame. The support unit supports the pelvis and legs of the user in a predetermined seating posture. A seatback assembly (22) is provided with a powered drive unit, to incline torso of the user along the forward direction from a vertical seating posture. A motor drives the drive unit, such that irrespective of the resistance by the user the torso of the user is inclined. An anchoring unit is provided for anchoring the seatback assembly, pivotably to the seat assembly, along the horizontal axis. The seatback assembly has constrained motion, relative to the seat assembly, along the vertical plane. Right and left hand grips (32) are provided in the seatback assembly for supporting the user's arms and hands relative to the torso, during use. The drive unit consists of a hydraulic power circuit with a double acting hydraulic servo.    The hydraulic servo is powered by the rotor. Several fluid conduits are provided in the hydraulic circuit for circulating fluids for power transmission. A drive control unit is provided to independently adjust upper and lower limits of the motion of the seatback assembly. An angle adjustment unit adjusts the angle of the seatback assembly relative to the seat assembly. A reversing switch with a trip bar is provided in the seatback assembly. First and second stop members are adjustably mounted to the frame for contacting the trip bar. The stop members contact the trip bar during inclination of the seatback assembly, to generate a signal for running the motor in reverse direction. The first and second stop members respectively contact the trip bar at upper and lower limits of the inclination of the seatback assembly. A signal transmission circuit is provided to transmit the signal when the top members contact the trip bar.    ADVANTAGE -   Enables simple control of speed during oscillation of seatback assembly. Widens application range.