Many of those who survive a stroke develop a gait disability known as stiff-knee gait (SKG). Characterized by reduced knee flexion angle during swing, people with SKG walk with poor energy efficiency and asymmetry due to the compensatory mechanisms required to clear the foot. Previous modeling studies have shown that knee flexion activity directly before the foot leaves the ground, and this should result in improved knee flexion angle during swing. The goal of this research is to physically test this hypothesis using robotic intervention. We developed a device that is capable of assisting knee flexion torque before swing but feels imperceptible (transparent) for the rest of the gait cycle. This device uses sheathed Bowden cable to control the deflection of a compliant torsional spring in a configuration known as a Series Elastic Remote Knee Actuator (SERKA). In this investigation, we describe the design and evaluation of SERKA, which includes a pilot experiment on stroke subjects. SERKA could supply a substantial torque (12 N·m) in less than 20 ms, with a maximum torque of 41 N·m. The device resisted knee flexion imperceptibly when desired, at less than 1 N·m rms torque during normal gait. With the remote location of the actuator, the user experiences a mass of only 1.2 kg on the knee. We found that the device was capable of increasing both peak knee flexion angle and velocity during gait in stroke subjects. Thus, the SERKA is a valid experimental device that selectively alters knee kinetics and kinematics in gait after stroke.

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Background: Adapting to external forces during walking has been proposed as a tool to improve locomotion after central nervous system injury. However, sensorimotor integration during walking varies according to the timing in the gait cycle, suggesting that adaptation may also depend on gait phases. In this study, an ElectroHydraulic AFO (EHO) was used to apply forces specifically during
mid-stance and push-off to evaluate if feedforward movement control can be adapted in these 2 gait phases. Methods: Eleven healthy subjects walked on a treadmill before (3 min), during (5 min) and after (5 min) exposure to 2 force fields applied by the EHO (mid-stance/push-off; ~10 Nm, towards dorsiflexion). To evaluate modifications in feedforward control, strides with no force field (‘catch strides’) were unexpectedly inserted during the force field walking period. Results: When initially exposed to a mid-stance force field (FF20%), subjects showed a significant increase in ankle dorsiflexion velocity. Catches applied early into the FF20% were similar to baseline (P > 0.99). Subjects gradually adapted by returning ankle velocity to baseline over ~50 strides. Catches applied thereafter showed decreased ankle velocity where the force field was normally applied, indicating the presence of feed-forward adaptation. When initially exposed to a push-off force field (FF50%), plantarflexion velocity was reduced in the zone of force field application. No adaptation occurred over the 5 min exposure. Catch strides kinematics remained similar to control at all times, suggesting no feedforward adaptation. As a control, force fields assisting plantarflexion (-3.5 to -9.5 Nm) were app-lied and increased ankle plantarflexion during push-off, confirming that the lack of kinematic changes during FF50% catch strides were not simply due to a large ankle impedance. Conclusion: Together these results show that ankle exoskeletons such as the EHO can be used to study phase-specific adaptive control of the ankle during locomotion. Our data suggest that, for short duration expo-sure, a feedforward modification in torque output occurs during mid-stance but not during push-off. These findings are important for the design of novel rehabilitation methods, as they suggest that the ability to use resistive force fields for training may depend on targeted gait phases.

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Many research groups are developing robotic exoskeletons which aim to assist motor rehabilitation for individuals after neurological injuries. As a rehabilitation tool, the primary goals of robotic exoskeletons are to reduce manual assistance from therapists and to achieve optimal training outcomes. Although the first objective has been realized by many current robotic devices, producing better rehabilitation outcomes with robotic devices is still a developing area of research. To design better robotic devices, it is important to understand the principles governing how humans learn to interact with the robotic assistance and to identify the gait parameters humans prioritize as objectives for their gait pattern. I used two types of robotic exoskeletons to examine rapid locomotor adaptation to mechanical assistance. The specific questions I addressed were: (1) how do neurologically intact subjects adapt their walking patterns to a powered orthosis that provides dorsiflexion assistance? (2) Do subjects walk with joint kinetic patterns during robotic-assisted walking similar to joint kinetic patterns during unassisted walking? (3) Is locomotor adaptation rate dependent on exoskeleton strength? (4) Is an increased stretch reflex inhibition a potential mechanism for reducing soleus recruitment when walking with the exoskeleton? (5) Do stretch reflex responses during unexpected gait perturbations appropriately meet the mechanical requirements of gait? In the first experiment, the exoskeleton was configured to provide dorsiflexion assistance proportional to the voluntary activation of the tibialis anterior muscle (i.e., ankle dorsiflexor). For the rest of experiments, the exoskeleton was configured with two artificial pneumatic muscles providing plantar flexion assistance proportional to the soleus muscle activation (i.e., ankle plantar flexor). The double muscle exoskeleton provided twice the mechanical capability of the previous single-muscle exoskeleton design (Cain et al. 2007; Gordon and Ferris 2007; Kinnaird and Ferris 2009). The results provide important insights into the principles governing human locomotor adaptation. The information can be used to aid in designing powered devices and may be helpful in optimizing gait rehabilitation therapies. In addition, the findings should be helpful in the development of biologically realistic neuromusculoskeletal computer simulations of human walking.

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This paper presents the design and the clinical vali-dation of an upper-limb force-feedback exoskeleton, the L-EXOS, for robotic-assisted rehabilitation in virtual reality (VR). The L-EXOS is a five degrees of freedom exoskeleton with a wearable structure and anthropomorphic workspace that can cover the full range of motion of human arm. A specific VR application focused on the reaching task was developed and evaluated on a group of eight post-stroke patients, to assess the efficacy of the system for the rehabilitation of upper limb. The evaluation showed a significant reduction of the performance error in the reaching task (paired t -test, p < 0.02). (далее…)

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A method for controlling movement using an active powered device including an actuator, joint position sensor, muscle stress sensor, and control system. The device provides primarily muscle support although it is capable of additionally providing joint support (hence the name “active muscle assistance device”). The device is designed for operation in several modes to provide either assistance or resistance to a muscle for the purpose of enhancing mobility, preventing injury, or building muscle strength. The device is designed to operate autonomously or coupled with other like device(s) to provide simultaneous assistance or resistance to multiple muscles.

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