Quadriceps Muscle Activity and Gait Kinematics in Patients With Post-Stroke Stiff-Knee Gait Compared With Healthy Controls

Stiff-knee gait (SKG) is a frequent gait abnormality in people with post-stroke hemiparesis and is characterized by insufficient knee flexion during the swing phase of walking. One potential mechanism is inappropriate activation of one or more heads of the quadriceps during pre-swing and early swing. This observational study will compare quadriceps electromyographic activity and gait kinematics between adults with chronic post-stroke hemiparesis with SKG and healthy adult controls. The study will include 30 participants with post-stroke SKG and 24 healthy controls. Quantitative gait analysis will be performed using three-dimensional motion analysis together with electromyography (EMG). Ultrasound-guided fine-wire electrodes will record the activity of all four heads of the quadriceps: rectus femoris, vastus intermedius, vastus medialis, and vastus lateralis. Healthy controls will be assessed while walking at a slow speed selected to provide a reference condition that is comparable with the walking speeds typically observed in participants with post-stroke hemiparesis. The primary outcome is the difference in fine-wire EMG activation patterns of the four quadriceps heads between participants with post-stroke SKG and healthy controls, with particular attention to pre-swing and early swing. Secondary outcomes will assess differences in gait kinematics between groups, including peak knee flexion during the swing phase and knee flexion-extension patterns throughout the gait cycle. The study aims to improve understanding of the muscular mechanisms underlying post-stroke SKG and to establish relevant fine-wire EMG reference patterns for all four quadriceps heads in healthy individuals walking at a speed comparable with patients with hemiparesis.