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

Stiff-knee gait (SKG) is a common gait impairment following stroke. It is characterized by insufficient knee flexion during the swing phase of walking and may interfere with foot clearance, increase the risk of falls, and lead to compensatory gait strategies associated with increased energy expenditure.

Several mechanisms have been proposed to explain SKG after stroke. These include weakness of the hip flexor muscles, reduced propulsion resulting from weakness of the ankle plantar flexors, and inappropriate or spastic activation of the quadriceps during pre-swing and early swing. Inappropriate quadriceps activity may oppose the passive knee flexion that normally develops during these phases of the gait cycle.

Determining whether individual quadriceps muscles demonstrate abnormal activation is difficult because quadriceps activity during normal walking varies both within and between individuals and is influenced by walking speed. This is particularly relevant when comparing healthy individuals with patients after stroke because patients with hemiparesis generally walk at slower speeds.

Existing normative electromyographic data for the quadriceps have several limitations. Published studies have generally investigated only some of the four quadriceps heads, and the deep vastus intermedius has been insufficiently characterized during walking. Furthermore, available reference data have not consistently been obtained at walking speeds comparable with those observed in people with post-stroke hemiparesis.

The primary objective of this study is to compare the electromyographic activity of the four quadriceps heads between participants with chronic post-stroke hemiparesis and stiff-knee gait and healthy adult controls.

A secondary objective is to compare gait kinematics between the two groups, particularly knee flexion during the swing phase, in order to investigate the relationship between altered quadriceps activation and the characteristic kinematic pattern of stiff-knee gait.

The study will include 24 healthy adult controls and 30 adults with chronic post-stroke hemiparesis with stiff-knee gait.

Healthy controls will undergo quantitative gait analysis at the RehaLAB of the Rehazenter. Ultrasound-guided fine-wire electrodes will be inserted into each of the four quadriceps heads: rectus femoris, vastus intermedius, vastus medialis, and vastus lateralis.

Healthy participants will be assessed while walking at a slow speed. This condition is selected because it is intended to provide a healthy reference dataset at a walking speed comparable with that typically observed in participants with post-stroke hemiparesis.

Participants in the stiff-knee gait group will undergo quantitative gait analysis using the same fine-wire EMG methodology for the four quadriceps heads. Three-dimensional lower-limb kinematics and surface EMG of selected additional lower-limb muscles will also be collected.

Fine-wire EMG is used rather than surface EMG for the quadriceps because selective assessment of individual quadriceps heads is required. Surface recordings may contain activity originating from adjacent muscles as a result of cross-talk, and the activity of the deep vastus intermedius cannot be adequately isolated using surface electrodes.

The primary analysis will compare fine-wire quadriceps EMG activation patterns between participants with stiff-knee gait and healthy controls assessed under the slow-speed reference condition. EMG signals will be evaluated over the time-normalized gait cycle. EMG envelopes will be estimated using the root mean square of the raw EMG signal. Particular attention will be paid to activation during pre-swing and early swing, during which inappropriate quadriceps activity may oppose normal knee flexion.

Each quadriceps head will be evaluated individually, including the rectus femoris, vastus intermedius, vastus medialis, and vastus lateralis.

Secondary analyses will compare gait kinematics between the two groups, with particular attention to sagittal-plane knee motion and peak knee flexion during the swing phase.

The primary statistical analysis will compare the time-normalized fine-wire EMG trajectories of each quadriceps head between participants with post-stroke stiff-knee gait and healthy controls assessed at the slow-speed reference condition.

The specific statistical method for this between-group comparison will be Statistical Parametric Mapping. Correction for multiple comparisons will be applied to the significance threshold.

The overall objective of the study is to establish detailed reference profiles of quadriceps activation during normal walking and determine how these profiles differ from those observed in people with post-stroke SKG. The study may help identify which quadriceps heads most frequently demonstrate atypical activation in SKG and improve understanding of the relationship between abnormal quadriceps activity and reduced knee flexion during the swing phase of gait.