Body weight support (BWS) systems are a common tool used in gait rehabilitation. BWS systems may alter the requirements for an individual to actively stabilize by 1) providing lateral restoring forces that reduce the requirements for the nervous system to actively stabilize and 2) decreasing the stabilizing gravitational moment in the frontal plane, which could increase the requirements to actively stabilize. The goal of the current study was to quantify the interaction between BWS and lateral stability. We hypothesized that when able-bodied people walk with BWS: 1) the lateral restoring forces provided by BWS would reduce the requirements to stabilize in the frontal plane when comparing dynamically similar gaits, and 2) increasing BWS would decrease the stabilizing gravitational moment in the frontal plane and increase the requirements to stabilize when speed is constrained. Our findings partly support these hypotheses, but indicate a complex interaction between BWS and lateral stability. With BWS, subjects significantly decreased step width variability and significantly increased step width (p < 0.05) for both the dynamically similar and speed-matched conditions. The decrease in step width variability may be attributable to a combination of lateral restoring forces decreasing the mechanical requirements to stabilize and an enhanced sense of position that could have improved locomotor control. Increases in step width when walking with high levels of BWS could have been due to decreases in the gravitational moment about the stance limb, which may challenge the control of stability in multiple planes.

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BackgroundStroke often leads to chronic, neural-derived motor impairments in the paretic lower limb, such as weakness, abnormal extensor torque coupling, and reduced ranges of motion. These impairments can constrain lower extremity movement and negatively impact the ability to navigate uneven terrain. Quantification of biomechanical strategies used by individuals with chronic stroke to step up would offer insight into the neural consequences of a stroke.Research QuestionWhat are the altered kinetic and kinematic strategies of the leading paretic hip and knee joints while swinging and pulling-up onto a step?MethodsA total of 10 participants were included in this mixed design study: 5 adults with hemiparetic stroke and 5 age-matched adults without stroke. Participants were instructed to step up onto a 4-inch platform, where joint kinetic and kinematics of the hip in the frontal plane and the hip and knee in the sagittal plane were quantified. A mixed effects linear regression model with two fixed effects of group (stroke and control) and lower limb (LL: dominant/non-paretic and non-dominant/paretic) was used to compare peak joint torques and angles. Another mixed effects model with two fixed effects of peak hip and knee extension torque was used to investigate whether these main effects could predict peak hip abduction torque.ResultsAltered biomechanical strategies of the paretic limb for step ascent included reduced sagittal plane flexion angles during swing, reduced hip abduction and knee extension torque combined with increased hip extension torque during pull-up stance, and abnormal torque coupling between the hip adductors and sagittal plane extensors.SignificanceThese differences can be linked to the neural consequences of a hemiparetic stroke, including corticospinal damage and upregulation of bulbospinal pathways as compensation. Overall, our findings can inform interventions for individuals with chronic stroke in navigating uneven terrain to maximize daily community activity.

Individuals with stroke often have difficulty modulating their lateral foot placement during gait, a primary strategy for maintaining lateral stability. Our purpose was to understand how individuals with and without stroke adapt their lateral foot placement when walking in an environment that alters center of mass (COM) dynamics and the mechanical requirement to maintain lateral stability. The treadmill walking environments included: 1) a Null Field – where no forces were applied, and 2) a Damping Field – where external forces opposed lateral COM velocity. To evaluate the response to the changes in environment, we quantified the correlation between lateral COM state and lateral foot placement (FP), as well as step width mean and variability. We hypothesized the Damping Field would produce a stabilizing effect and reduce both the COM-FP correlation strength and step width compared to the Null Field. We also hypothesized that individuals with stroke would have a significantly weaker COM-FP correlation than individuals without stroke. Surprisingly, we found no differences in COM-FP correlations between the Damping and Null Fields. We also found that compared to individuals without stroke in the Null Field, individuals with stroke had weaker COM-FP correlations (Paretic < Control: p = 0.001, Non-Paretic < Control: p = 0.007) and wider step widths (p = 0.001). Our results suggest that there is a post-stroke shift towards a non-specific lateral stabilization strategy that relies on wide steps that are less correlated to COM dynamics than in individuals without stroke.