Award Date

5-15-2026

Degree Type

Doctoral Project

Degree Name

Doctor of Physical Therapy (DPT)

Department

Physical Therapy

First Committee Member

Jing Nong Liang

Second Committee Member

Daniel Young

Third Committee Member

Kai-Yu Ho

Number of Pages

35

Abstract

Purpose/Hypothesis

Leg stiffness is regulated by reflexive, intrinsic, and passive mechanisms, which are influenced by posture, body weight loading, and motor task demands. After a stroke, the capacity to modulate these mechanisms is often compromised. The H-reflex is a widely used electrophysiological tool to assess the excitability of the Ia afferent pathway within spinal circuitry. Although prior studies in healthy individuals have examined limb loading effects, results have been variable, and the role of postural and loading changes during standing remains underexplored, particularly in individuals post-stroke. This study investigated how different postural and limb loading conditions, specifically prone, standing, and weighted standing, affect the H-reflex excitability in individuals after stroke. We hypothesized that H-reflex amplitudes would decrease from prone to standing, and increase with greater limb loading in neurologically intact individuals, whereas H-reflex modulation would be impaired in individuals after stroke in both non-paretic and paretic limbs.

Number of Subjects

Fifteen individuals with chronic post-stroke hemiparesis and ten non-neurologically impaired controls participated.

Material and Methods

Participants completed three conditions: prone, standing, and weighted standing with 20% body weight added via a weighted vest. Surface electromyography (EMG) was recorded from the soleus (SOL) muscle using self-adhesive Ag-AgCl electrodes. For individuals post-stroke, EMG was collected from both paretic and non-paretic limbs; for controls, recordings were taken from the right leg unless the participant indicated a preference. The tibial nerve was electrically stimulated across a range from subthreshold to the maximal M-wave (Mmax) to generate a SOL recruitment curve, from which the maximal H-reflex and its corresponding control M-wave were identified. A stimulation intensity corresponding to 50% of the control M- wave was used to ensure the test reflex was on the ascending limb of the recruitment curve. For each loading condition, 20 stimuli were delivered, and peak-to-peak H-reflex amplitudes were averaged and normalized to Mmax (H/M ratio). A 3 (Limb: paretic, non-paretic, non-impaired) x 3 (Loading: prone, standing, weighted standing) mixed factorial ANOVA was conducted to assess differences in H-reflex modulation. A priori significance was set at p < 0.05.

Results

A significant Limb × Loading interaction was observed (F(2.49, 44.85) =6.06, p =0.003, η²=0.25) for the H/Mmax. Simple effects revealed that, in the non-impaired limb, decreased H-reflex amplitude from prone to standing, then increased with weighted standing. In the non-paretic limb, H-reflex amplitudes increased from prone to standing and further increased with weighted standing. No significant modulation was observed in the paretic limb across loading conditions.

Conclusions

Findings indicate impaired H-reflex modulation in the non-paretic limb and absent modulation in the paretic limb following stroke, suggesting impaired neural adaptability to postural and loading changes in individuals with chronic post-stroke hemiparesis.

Clinical Relevance

Insights into impaired H-reflex modulation in response to posture and loading after stroke can guide the development of targeted interventions aimed at improving post-stroke motor function.

Keywords

Post-stroke Hemiparesis; Hoffman Reflex; Postural Loading

Disciplines

Neuroscience and Neurobiology | Physical Therapy

File Format

PDF

File Size

449 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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