Contribution of Feedback and Feedforward Strategies to Locomotor Adaptations

• Published in: Journal of neurophysiology 2006-02, Vol.95 (2), p.766-773
• Main Authors: Lam, Tania, Anderschitz, Martin, Dietz, Volker
• Format: Article
• Language: English
• Subjects: Adaptation, Physiological - physiology; Adult; Feedback - physiology; Female; Gait - physiology; Humans; Joints - physiology; Leg - physiology; Male; Muscle Contraction - physiology; Muscle, Skeletal - physiology; Physical Exertion - physiology; Postural Balance - physiology; Range of Motion, Articular - physiology; Walking - physiology
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.00473.2005

1 Spinal Cord Injury Center, Balgrist University Hospital; and 2 Rehabilitation Engineering Group, Automatic Control Laboratory, Swiss Federal Institute of Technology, Zurich, Switzerland Submitted 9 May 2005; accepted in final form 20 October 2005 The aim of this study was to examine the strategies used by human subjects to adapt their walking pattern to a velocity-dependent resistance applied against hip and knee movements. Subjects first walked on a treadmill with their lower limbs strapped to an exoskeletal robotic gait orthosis with no resistance against leg motions (null condition). Afterward, a velocity-dependent resistance was applied against left hip and knee movements (force condition). Catch trials were interspersed throughout the experiment to track the development of adaptive changes in the walking pattern. After 188 steps in the force condition, subjects continued to step in the null condition for another 100 steps (washout period). Leg muscle activity and joint kinematics were recorded and analyzed. The adaptive modifications in the locomotor pattern suggest the involvement of both feedback and feedforward control strategies. Feedback-driven adaptations were reflected in increases in rectus femoris and tibialis anterior activity during swing, which occurred immediately, only in the presence of resistance, and not during the catch trials. Locomotor adaptations involving feedforward strategies were reflected in enhanced pre-swing activity in the biceps femoris and medial hamstrings muscles, which required experience and persisted in the catch trials. During washout subjects showed a gradual deadaptation of locomotor activity to control levels. In summary, adaptive changes in the walking pattern were driven by both feedback and feedforward adjustments in the walking pattern appropriate for overcoming the effects of resistance. Address for reprint requests and other correspondence: T. Lam, School of Human Kinetics, University of British Columbia, 210-6081 University Blvd., Vancouver, BC V6T 1Z1, Canada (E-mail: tania.lam{at}ubc.ca )