Millions of individuals suffer from gait impairments due to stroke or other neurological disorders. A primary goal of patients is to walk independently, but most patients only achieve a poor functional outcome five years after injury. Despite the growing interest in using robotic devices for rehabilitation of sensorimotor function, state-of-the-art robotic interventions in gait therapy have not resulted in improved outcomes when compared to traditional treadmill-based therapy. Because bipedal walking requires neural coupling and dynamic interactions between the legs, a fundamental understanding of the sensorimotor mechanisms of inter-leg coordination during walking is needed to inform robotic interventions in gait therapy. This dissertation presents a systematic exploration of sensorimotor mechanisms of inter-leg coordination by studying the effect of unilateral perturbations of the walking surface stiffness on contralateral muscle activation in healthy populations. An analysis of the contribution of several sensory modalities to the muscle activation of the opposite leg provides new insight into the sensorimotor control mechanisms utilized in human walking, including the role of supra-spinal neural circuits in inter-leg coordination. Based on these insights, a model is created which relates the unilateral deflection of the walking surface to the resulting neuromuscular activation in the opposite leg. Additionally, case studies with hemiplegic walkers indicate the existence of the observed mechanism in neurologically impaired walkers. The results of this dissertation suggest a novel approach to gait therapy for hemiplegic patients in which desired muscle activity is evoked in the impaired leg by only interacting with the healthy leg. One of the most significant advantages of this approach over current rehabilitation protocols is the safety of the patient since there is no direct manipulation of the impaired leg. Therefore, the methods and results presented in this dissertation represent a potential paradigm shift in robot-assisted gait therapy.

Leg stiffness is an important factor in human walking. Understanding the ways in which stiffness impacts walking could lead to improvements in gait rehabilitation, exoskeleton design, and exoskeleton control. Three studies were conducted to better understand the effects of stiffness on walking. The first study investigated how changing stiffness of the foot itself affects walking. To do this, a rigid foot plate was attached to the foot of 16 subjects in order to increase the stiffness of the foot. This is because many exoskeletons and orthoses use a rigid foot plate, but this may affect the natural mechanics of the foot. The resulting spatiotemporal parameters, kinematics, and kinetics were compared with normal walking. It was found that the foot plate did not have an effect on spatiotemporal parameters, but did decrease the ankle range of motion and decreased the intersegmental motion of the different parts of the foot. It was also found that a foot plate that ends before the toes has less of an effect than a foot plate that extends to the end of the toes. Therefore, exoskeletons and orthoses should implement a jointed toe segment or a shorter foot plate in order to increase the transparency of the device. For the second study, an ankle exoskeleton was developed with the requirement that it was capable of a versatile range of control modes, and was robust. Versatility is important for an exoskeleton because the type of rehabilitation a person may require can vary due to a number of factors. The exoskeleton must also be robust in uncertain environments because humans undergoing rehabilitation may act unpredictably. Therefore, a pneumatically powered exoskeleton was designed and controlled using sliding mode control. This exoskeleton is capable of position, force, and impedance control. Four subjects were used to test the performance of these controllers while following position and force trajectories. The tests showed that regardless of the behavior of the wearer, the exoskeleton acted appropriately and under an acceptable degree of error. This demonstrates that sliding mode control can be used to make exoskeletons capable of the versatility required for rehabilitation. Lastly, in the third study, the control of leg stiffness while walking was investigated. This was done by using human data from 12 subjects to extract system models and leg stiffness controllers for walking using three different methods and informed by the spring-loaded inverted pendulum model. The first method used ordinary least squares to linearize the system about a Poincaré section; the second linearized the spring-loaded inverted pendulum model and combined that with the results from the first method. The third method used the sparse identification of nonlinear dynamics procedure to identify linear combinations of nonlinear functions that describe the system. These methods were evaluated based on how well they predicted experimental data, and based on how well they controlled a spring-loaded inverted pendulum model walker in simulation. Results showed that all three methods resulted in similarly accurate models and controllers. Therefore, using human data in conjunction with data driven identification techniques may be used to reveal the mechanics of gait or to design robotic controllers for walking.

This comprehensive edited treatise discusses the neurological, physiological, and cognitive aspects of interlimb coordination. It is unique in promoting a multidisciplinary perspective through introductory chapter contributions from experts in the neurosciences, experimental and developmental psychology, and kinesiology. Beginning with chapters defining the neural basis of interlimb coordination in animals, the book progresses toward an understanding of human locomotor control and coordination and the underlying brain structures and nerves that make such control possible. Section two focuses on the dynamics of interlimb coordination and the physics of movement. The final section presents information on how practice and experience affect coordination, including general skill acquisition, learning to walk, and the process involved in rhythmic tapping.

Neurorehabilitation Technology provides an accessible, practical overview of the all the major areas of development and application in the field. The initial chapters provide a clear, concise explanation of the rationale for robot use and the science behind the technology before proceeding to outline a theoretical framework for robotics in neurorehabilitative therapy. Subsequent chapters provide detailed practical information on state-of-the-art clinical applications of robotic devices, including robotics for locomotion; posture and balance and upper extremity recovery in stroke and spinal cord injury. Schematic diagrams, photographs and tables will be included to clarify the information for the reader. The book also discusses standard and safety issues and future perspectives.