Impaired H-Reflex Gain during Postural Loaded Locomotion in Individuals Post-Stroke

Abstract

ObjectiveSuccessful execution of upright locomotion requires coordinated interaction between controllers for locomotion and posture. Our earlier research supported this model in the non-impaired and found impaired interaction in the post-stroke nervous system during locomotion. In this study, we sought to examine the role of the Ia afferent spinal loop, via the H-reflex response, under postural influence during a locomotor task. We tested the hypothesis that the ability to increase stretch reflex gain in response to postural loads during locomotion would be reduced post-stroke.MethodsFifteen individuals with chronic post-stroke hemiparesis and 13 non-impaired controls pedaled on a motorized cycle ergometer with specialized backboard support system under (1) seated supported, and (2) non-seated postural-loaded conditions, generating matched pedal force outputs of two levels. H-reflexes were elicited at 90°crank angle.ResultsWe observed increased H-reflex gain with postural influence in non-impaired individuals, but a lack of increase in individuals post-stroke. Furthermore, we observed decreased H-reflex gain at higher postural loads in the stroke-impaired group.ConclusionThese findings suggest an impaired Ia afferent pathway potentially underlies the defects in the interaction between postural and locomotor control post-stroke and may explain reduced ability of paretic limb support during locomotor weight-bearing in individuals post-stroke.SignificanceThese results support the judicious use of bodyweight support training when first helping individuals post-stroke to regain locomotor pattern generation and weight-bearing capability.

Slow Walking in Individuals with Chronic Post-Stroke Hemiparesis: Speed Mediated Effects of Gait Kinetics and Ankle Kinematics

“…When demands for postural loads have been alleviated, the stroke-impaired system was capable of generating foot forces that are appropriately controlled in magnitude and direction [ 13 ]. However, this appropriate foot-force control capability was disrupted under more challenging conditions, when individuals post-stroke have to simultaneously control for postural loads in addition to the locomotor task [ 22 , 23 ], comparable to overground/treadmill walking conditions. This inability to modulate braking impulse with reduction in speed can pose safety threats for individuals with chronic post-stroke hemiparesis.…”

Immediate Effects of Anodal Transcranial Direct Current Stimulation on Postural Stability Using Computerized Dynamic Posturography in People With Chronic Post-stroke Hemiparesis

“…Medium latency responses via the brainstem are likely responsible for these functional postural responses, in combination with the cerebellum, which adapts postural responses for optimality based on preceding experience (Jacobs and Horak, 2007). Although the impaired adaptation of the Ia afferent pathway via the spinal cord has been reported in tasks involving postural control and locomotion in people chronically post-stroke (Liang and Brown, 2015;Liang et al, 2019), they are likely not the main contributor to this observed improvement, as short-latency reflex pathway via the spinal cord is too weak to be functional for postural control.…”

Altered Achilles tendon morphology in individuals with chronic post-stroke hemiparesis: a case report

“…It would be important to explore the time course of adaptations. Additionally, future studies should address multi-level adaptations by examining the contribution of the altered neural circuitry post-stroke [8,9].…”