A split-crank bicycle ergometer uses servomotors to provide programmable pedal forces for studies in human biomechanics

FES Cycling and Closed-Loop Feedback Control for Rehabilitative Human–Robot Interaction

For individuals with movement impairments due to neurological injuries, rehabilitative therapies such as functional electrical stimulation (FES) and rehabilitation robots hold vast potential to improve their mobility and activities of daily living. Combining FES with rehabilitation robots results in intimately coordinated human–robot interaction. An example of such interaction is FES cycling, where motorized assistance can provide high-intensity and repetitive practice of coordinated limb motion, resulting in physiological and functional benefits. In this paper, the development of multiple FES cycling testbeds and safeguards is described, along with the switched nonlinear dynamics of the cycle–rider system. Closed-loop FES cycling control designs are described for cadence and torque tracking. For each tracking objective, the authors’ past work on robust and adaptive controllers used to compute muscle stimulation and motor current inputs is presented and discussed. Experimental results involving both able-bodied individuals and participants with neurological injuries are provided for each combination of controller and tracking objective. Trade-offs for the control algorithms are discussed based on the requirements for implementation, desired rehabilitation outcomes and resulting rider performance. Lastly, future works and the applicability of the developed methods to additional technologies including teleoperated robotics are outlined.

Design and Validation of a Lower-Limb Haptic Rehabilitation Robot

Present robots for investigating lower-limb motor control and rehabilitation focus on gait training. An alternative approach is to focus on restoring precursor abilities such as motor adaptation and volitional movement, as is common in upper-limb robotic therapy. Here we describe NOTTABIKE, a one degree-of-freedom rehabilitation robot designed to probe and promote these underlying capabilities. A recumbent exercise cycle platform is powered with a servomotor and instrumented with angular encoders, force-torque sensing pedals, and a wireless EMG system. Virtual environments ranging from spring-mass-damper systems to novel foot-to-crank mechanical laws present variants of leg-reaching and pedaling tasks that challenge perception, cognition, motion planning, and motor control systems. This paper characterizes the dynamic performance and haptic rendering accuracy of NOTTABIKE and presents an example motor adaptation task to illustrate its use. Torque and velocity mode controllers showed near unity magnitude ratio and phase loss less than 60 degrees up to 10 Hz. Spring rendering demonstrated 1% mean error in stiffness, and damper rendering performed comparably at 2.5%. Virtual mass rendering was less accurate but successful in varying perceived mass. NOTTABIKE will be used to study lower-limb motor adaptation in intact and impaired persons and to develop rehabilitation protocols that promote volitional movement recovery.

Visual feedback during pedaling allows individuals poststroke to alter inappropriately prolonged paretic vastus medialis activity

Individuals who have experienced a stroke often demonstrate inappropriate muscle activity phasing in the paretic leg during locomotion. Past research has demonstrated that inappropriate paretic phasing varies between behavioral contexts and is reduced during unilateral pedaling with the nonparetic leg inactive. We investigated whether individuals could voluntarily alter activity in a target muscle of the paretic limb in a consistent behavioral context and whether this voluntary change differed between bilateral and unilateral pedaling. During a fixed-speed motorized pedaling task, participants were asked to use visual feedback to deactivate the vastus medialis (VM) before a 90° target region of the pedaling cycle, as measured by surface electromyography and by change in fraction of total cycle amplitude in the target region. We based the start of this target region on the earliest observed deactivation for this muscle (found in fast pedaling), which allowed us to challenge both the paretic and nonparetic VM. During visual feedback, participants significantly reduced the fraction of activity found in the target region, with no significant difference in degree of reduction between paretic and nonparetic legs or between bilateral and unilateral pedaling. Surprisingly, in bilateral pedaling, individuals with greater clinical impairment demonstrated greater paretic limb response to feedback. Our results demonstrated that during this tightly constrained task, the paretic VM showed a surprisingly similar flexibility of muscle activity to the nonparetic VM. Our findings show that participants were able to use provided visual feedback to modulate the degree of an observed poststroke muscle-phasing impairment. NEW & NOTEWORTHY This study demonstrates that by using visual feedback during a constrained task with minimized kinematic control requirements, participants with poststroke hemiplegia can voluntarily change muscle activity phase in the vastus medialis. Surprisingly, we did not observe a significant difference in ability to alter phasing between paretic and nonparetic legs or between bilateral and unilateral pedaling. In this visual feedback task, participants appear to modify muscle activity well in both the paretic and nonparetic legs.