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.
Highlights
Limb stiffness regulation is a function of reflex, intrinsic and passive components and is modulated relative to the phase in locomotor tasks, such as walking [1,2,3,4,5]
These 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 poststroke
In earlier studies examining the Ia afferent spinal loop, common measured variables include peak-to-peak H-reflex amplitudes under matched background muscle activity[7, 8], H-reflex gain from the slope relationship between H-reflex amplitude and EMG amplitude across a range of EMG levels [5, 9], and H-reflex gain defined as the ratio of H-reflex amplitude to average background muscle activity [10, 11] used as functional measures of reflex modulation
Summary
Limb stiffness regulation is a function of reflex, intrinsic and passive components and is modulated relative to the phase in locomotor tasks, such as walking [1,2,3,4,5]. In the non-impaired nervous system, during walking, the soleus (SOL) H-reflex amplitude increases in a ramp-like fashion in parallel with SOL muscle activity during the stance/loading phase, and strongly suppressed during the swing/non-loading phase [3,4,5, 12], contributing functionally to force production, load compensation, and body weight support during stance, and assist with propulsion [13, 14]. Under comparable postural conditions, earlier studies using various protocols reported inconsistent findings regarding the effects of limb loading on H-reflex amplitude [24,25,26,27,28,29,30,31]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
