Abstract
Background and Purpose Short term adaptations in the Ia afferent-motoneuron pathway, as measured using the H-reflex, in response to altered ground reaction forces (GRFs) applied at the feet during slope walking have been observed in the non-impaired nervous system. The ability of the stroke-impaired nervous system to adapt to altered GRFs have not been examined. The purpose of this study was to examine the acute effects of altered propulsive and braking forces applied at the feet, which naturally occurs when walking on different slopes, on adaptations of the H-reflex pathway in individuals with chronic post-stroke hemiparesis.MethodsTwelve individuals chronically post-stroke and 10 age-similar non-neurologically impaired controls walked on an instrumented treadmill for 20 min under level, upslope and downslope conditions. GRFs were measured during walking and soleus H-reflexes were recorded prior to and immediately after walking. A 3 (limbs: paretic, non-paretic, and non-impaired) × 3 (slope: level, upslope, downslope) mixed factorial ANOVA was conducted on the propulsive and braking forces. A 2 (limb: paretic and non-impaired) × 2 (time: pre and post) × 3 (slope: level, upslope, and downslope) mixed factorial ANOVA was conducted to assess the soleus H-reflex amplitudes.ResultsIn both post-stroke and non-impaired groups, during downslope walking, peak propulsive forces decreased, while peak braking forces increased. In contrast, during upslope walking, peak propulsive forces increased and peak braking forces decreased. We observed reduced soleus H-reflex amplitudes immediately following 20 min of level, downslope and upslope walking in non-impaired individuals but not in the paretic legs of individuals with chronic post-stroke hemiparesis.Discussion and ConclusionSimilar pattern of change in peak propulsive and braking forces with respect to different slopes was observed in both individuals post-stroke and non-impaired individuals, but the magnitude of GRFs were smaller in individuals post-stroke due to the slower walking speed. Our results suggested that impaired modulation of the H-reflex pathway potentially underlies the lack of neuroadaptations in individuals with chronic post-stroke hemiparesis.
Highlights
Stroke is the leading cause of long-term adult disabilities (Benjamin et al, 2018)
The primary purpose of this study was to examine the immediate effects of altered propulsive and braking forces applied at the feet, which naturally occurs when walking on different slopes, on adaptations of the Ia afferent pathway, as measured using the H-reflex, in individuals with chronic poststroke hemiparesis
Despite the slower walking speed for upslope walking, heart rate was higher following upslope compared to downslope and level, for both groups (Table 1)
Summary
Stroke is the leading cause of long-term adult disabilities (Benjamin et al, 2018). While majority of stroke survivors regain independent ambulation, there often remains impaired motor control, and limitations in walking, which can present as a safety concern when participating in daily physical activities (Olney and Richards, 1996).To execute successful locomotion, leg muscles have to be coordinated so as to generate foot forces of appropriate magnitude and direction to propel the center of mass forward (Neptune et al, 2001). In individuals with chronic post-stroke hemiparesis, inappropriate direction of foot forces during locomotion has been reported (Bowden et al, 2006; Turns et al, 2007; Liang and Brown, 2013, 2014), reduced propulsive forces accompanied by exaggerated braking forces have been observed in paretic legs (Olney and Richards, 1996; Bowden et al, 2006; Turns et al, 2007). The purpose of this study was to examine the acute effects of altered propulsive and braking forces applied at the feet, which naturally occurs when walking on different slopes, on adaptations of the H-reflex pathway in individuals with chronic post-stroke hemiparesis
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