The role of load-regulating mechanisms In gaze stabilization during locomotion

The whole body acts as a gaze stabilization system: head-torso activity and lower body movement are coordinated to provide a stable retinal image during locomotion. Body loading is a fundamental parameter that modulates motor output during locomotion, and is especially important for controlling the generation of stepping patterns, dynamic balance, and termination of locomotion. Increased body weight support (BWS) during locomotion results in an immediate reorganization of locomotor control, such as a reduction in stance and double support duration and decreased hip, ankle, and knee angles during the gait cycle. Until now, no studies have investigated how gaze control systems respond to adaptive modification in the body load sensing system. The goal of this research is to determine the role of body load-regulating mechanisms in gaze control during locomotion. The general hypothesis behind the proposed research is that body load-regulating mechanisms contribute to gaze stabilization, and adaptive changes in these load-regulating mechanisms will require reorganization in the full-body gaze control system so that visual acuity can be maintained during locomotion. \r\nTo support the hypothesis of this study, head-torso coordination, lower limb movement patterns, and gait cycle timing were evaluated before and after a 30-minute adaptation session during which subjects walked on a treadmill at 5.4 km/hr with 40% body weight support (BWS). Before and after the adaptation period, head-torso and lower limb 3D kinematic data were obtained during locomotion using a video-based motion analysis system, and gait cycle timing parameters were collected by foot switches positioned under the heel and toe of the subjects’ shoes. The predominant changes observed in the subjects were a result of adaptive modification in the body load-regulating mechanisms and included increased head movements, increased knee and ankle flexion, and increased stance, stride, and double support time, with no change in dynamic visual acuity. Therefore, it is evident that just 30 minutes of 40% BWS during locomotion was enough sensory conflict to induce adaptive modifications in the sensory systems that contribute to locomotor control, and these modifications represent an overall reorganization of vestibular-somatosensory interactions in the full-body integrated gaze stabilization system. \r\n