Changes in passive ankle stiffness and its effects on gait function in people with chronic stroke

Abstract

Abstract-Mechanical impedance of the ankle is known to influence key aspects of ankle function. We investigated the effects of robot-assisted ankle training in people with chronic stroke on the paretic ankle's passive stiffness and its relationship to overground gait function. Over 6 wk, eight participants with residual hemiparetic deficits engaged in a visuomotor task while seated that required dorsiflexion (DF) or plantar flexion (PF) of their paretic ankle with an ankle robot ("anklebot") assisting as needed. Passive ankle stiffness (PAS) was measured in both the trained sagittal and untrained frontal planes. After 6 wk, the PAS decreased in both DF and PF and reverted into the variability of age-matched controls in DF. Changes in PF PAS correlated strongly with gains in paretic step lengths (Spearman rho = 0.88, p = 0.03) and paretic stride lengths (Spearman rho = 0.82, p = 0.05) during independent floor walking. Moreover, baseline PF PAS were correlated with gains in paretic step lengths (Spearman rho = 0.94, p = 0.01), paretic stride lengths (Spearman rho = 0.83, p = 0.05), and singlesupport stance duration (Spearman rho = 0.94, p = 0.01); and baseline eversion PAS were correlated with gains in cadence (Spearman rho = 0.88, p = 0.03). These findings suggest that ankle robot-assisted, visuomotor-based, isolated ankle training has a positive effect on paretic ankle PAS that strongly influences key measures of gait function.

Increased reward in ankle robotics training enhances motor control and cortical efficiency in stroke

“…Mounting evidence suggests that lower-limb (LL) motor-learning based interventions can improve movement function even years after a debilitating stroke [8][9][10][11][12][13][14][15][16][17]. This notion is supported by reports that treadmill-based locomotor training programs can improve gait velocity and elicit changes in cortical and subcortical neural networks associated with paretic LL movements [18][19][20][21].…”

“…As highlighted in a Cochrane review [15], there are potential benefits from using LL robotics poststroke, but we have much to learn about optimal interventions. Robotic devices can provide a useful platform for assessing comparative effectiveness of different motor learning strategies by providing versatile, interactive, task-specific training; a capacity to integrate or reward performance feedback; and the ability to precisely measure the rate and magnitude of key descriptors of motor-performance variables [10][11][12][14][15][20][21]. In the past several years, the Baltimore Department of Veterans Affairs (VA) Medical Center, in collaboration with the Massachusetts Institute of Technology, has developed and deployed in the clinic an impedancecontrolled, modular, 2 degree of freedom (DOF)-actuated ankle robot exoskeleton (anklebot, Interactive Motion Technologies; Watertown, Massachusetts), to improve walking and balance functions poststroke by means of increasing the paretic ankle contribution during taskoriented functional activities.…”

“…Thus, our choice of using the anklebot for this study was based in part on the flexible, interactive platform it affords for implementing motorlearning paradigms and its ability to assay the temporal profile of motor performance across training. For example, our prior studies have shown that changes in passive ankle stiffness in the inversion-eversion plane to be a strong predictor of improvements in independent floor-walking speed in patients with chronic stroke [12], Similarly, movement smoothness (characterized by jerk normalized to peak movement speed) has been used to characterize motor recovery for both the upper limb and LL [10][11][24][25][26]. Notably and relevant to this study, seated anklebot training allows for the collection of viable electroencephalography (EEG) signal with minimal movement artifact, thus fostering study of the cortical dynamics associated with motor learning.…”

The Impact of Aging and Hand Dominance on the Passive Wrist Stiffness of Squash Players: Pilot Study (Preprint)

“…Reduced joint stiffness may increase the risk of injury due to poor stabilization of joints and an inability to maintain joint postures [1,2]. Increased joint stiffness has been associated with reduced joint range of motion and inflexibility which can cause both injury and functional limitations, such as during the aging process [3,4], following surgical intervention [5], or because of abnormal muscle tone secondary to neurological injury or disease [6,7].…”

“…This study focuses on the measurement of passive joint quasi-stiffness, defined as the rate of change of resistance torque during a slow angular displacement of the joint, in the absence of muscle contraction [1,12]. Extensive research has been conducted on passive joint quasi-stiffness of the lower limb and the impact on gait [6,7], with less research focusing on the upper limb and the equally important impact on activities of daily living, leisure activities, and sports. Of the joints within the upper limb, the neuromuscular control of the wrist has been identified as being dominated by joint stiffness [13,14].…”