an electromechanical device that provides a spot to a weightlifter performing a weightlifting exercise . the device has a metal frame that supports two arms , called spotter arms . the two spotter arms extend out so as to be able to support a barbell . the arms raise and lower on the frame , remaining parallel with the floor and perpendicular to the frame and are powered by a motor driven lead screw . the operation of the motor is controlled by a computer control system . the input to the control system is provided by a load - cell mounted in one of the two spotter arms . when the control system is operating in the spot mode , the load - cell measures the amount of force that is placed on the spotter arm by the barbell held by the weightlifter . the control system then moves the spotter arms in accordance with the amount of force on the load - cell in order to provide a safe spot thereby increasing the effectiveness of the exercise . the load - cell is mounted within a hollow interior of one of the spotter arms . a mechanical assembly that transfers the force of the barbell supported by the arms to the load - cell is also contained within the hollow interior of the spotter arm .