Abstract: An isokinetic resistance exerciser in the form of a treadmill is the subject of the present invention. An improved isokinetic resistance is provided by oversized frictional members and flat centrifugal plates which respond to centrifugal forces to cause inter-engagement of the frictional surfaces. The invention also includes a centrifugally-responsive speed register mechanism and a device for recording the total work expended by a person exercising. The centrifugally-responsive actuating mechanism employing flat plates in place of conventional weights results in improved operating characteristics.