A cable-driven locomotor training system for restoration of gait in human SCI Ming Wu a,b, *, T. George Hornby a,b,c , Jill M. Landry a , Heidi Roth a , Brian D. Schmit a,b,d a Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL, USA b Department of Physical Medicine and Rehabilitation, Northwestern University Medical School, Chicago, IL, USA c Department of Physical Therapy, University of Illinois at Chicago, Chicago, IL, USA d Department of Biomedical Engineering, Marquette University, P.O. Box 1881, Milwaukee, WI 53201-1881, USA 1. Introduction Body weight supported treadmill training (BWSTT) is a promis- ing rehabilitation method designed to improve motor function and ambulation in people with spinal cord injury (SCI) [1–5]. During BWSTT, the patient is given body weight support through a harness and their legs are moved by physical therapists in a ‘‘kinematically correct gait’’ [1]. This training paradigm is task-specific, utilizes both motor and sensory pathways of the relevant neuromuscular systems and has been shown to provide significant improvements in locomotor function [6]. However, a major limitation of BWSTT is that it requires considerable involvement of a physical therapist and is labor intensive. Thus, a robotic system that controls the stepping environment is an appealing approach to BWSTT. Several robotic systems have been developed for automating locomotor training, such as the Lokomat [7] and the Gait Trainer (GT) [8]. The Lokomat is a motorized exoskeleton that drives hip and knee motion in a fixed trajectory using four DC motors [7], but it is difficult to back-drive the Lokomat because it uses high-advantage, ball screw actuators. The GT rigidly drives the patient’s feet through a stepping motion using a crank-and-rocker mechanism attached to foot platforms [8]. These robotic systems are effective in reducing therapist labor during locomotor training and increasing the total duration of training, but can show relatively limited functional gains for some patients [4,5]. The reduced effectiveness may be due to a tendency to produce less effort during fixed trajectory motion [9]. In addition, fixed-trajectory training eliminates the variability in kinematics of the lower limbs, which is thought to be critical for successful motor adaptation, as demonstrated in both animal [10] and human studies [11]. The limited degrees of freedom of the Lokomat only allow movement of the limbs in the sagittal plane, which may affect gait dynamics [12,13]. As a consequence, there is a need for a robotic system that provides a more compliant assistance and encourages active involvement of the patient during gait training. In this study, we tested a novel, compliant, cable-driven robotic system that provides controlled forces to the legs during the early swing phase of gait. The system was designed to allow more freedom for the subjects to voluntarily move their legs during BWSTT. We tested the feasibility of using the cable-driven locomotor trainer (CaLT) for gait training in 11 subjects with incomplete SCI. Gait & Posture 33 (2011) 256–260 ARTICLE INFO Article history: Received 9 August 2010 Accepted 18 November 2010 Keywords: Robotic locomotor training Cable actuated Spinal cord injury ABSTRACT A novel cable-driven robotic locomotor training system was developed to provide compliant assistance/ resistance forces to the legs during treadmill training in patients with incomplete spinal cord injury (SCI). Eleven subjects with incomplete SCI were recruited to participate in two experiments to test the feasibility of the robotic gait training system. Specifically, 10 subjects participated in one experimental session to test the characteristics of the robotic gait training system and one subject participated in repeated testing sessions over 8 weeks with the robotic device to test improvements in locomotor function. Limb kinematics were recorded in one experiment to evaluate the system characteristics of the cable-driven locomotor trainer and the overground gait speed and 6 min walking distance were evaluated at pre, 4 and 8 weeks post treadmill training of a single subject as well. The results indicated that the cable driven robotic gait training system improved the kinematic performance of the leg during treadmill walking and had no significant impact on the variability of lower leg trajectory, suggesting a high backdrivability of the cable system. In addition, results from a patient with incomplete SCI indicated that prolonged robotic gait training using the cable robot improved overground gait speed. Results from this study suggested that a cable driven robotic gait training system is effective in improving leg kinematic performance, yet allows variability of gait kinematics. Thus, it seems feasible to improve the locomotor function in human SCI using this cable driven robotic system, warranting testing with a larger group of patients. ß 2010 Elsevier B.V. All rights reserved. * Corresponding author at: Sensory Motor Performance Program, Rehabilitation Institute of Chicago, 345 East Superior Street, Room 1406, Chicago, IL 60611, USA. Tel.: +1 312 238 0700; fax: +1 312 238 2208. E-mail address: w-ming@northwestern.edu (M. Wu). Contents lists available at ScienceDirect Gait & Posture journal homepage: www.elsevier.com/locate/gaitpost 0966-6362/$ – see front matter ß 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.gaitpost.2010.11.016