How Are Muscle-activation Changes in PFPS Related to the Sagittal Knee Moment during Walking?

The PFPS group had lower knee-extension moment during weight acceptance, without a significant difference in flexion angle. ST activity was higher throughout gait.

Blue lines show control-group means and red lines show PFPS-group means across the gait cycle. Angles, knee-extension moments, and EMG from four muscles are aligned on the same time axis.
Byung Sun Choi, Soon Bin Kwon, Sehyeon Jeon, Myeongjun Kim, Yunseo Ku, Du Hyun Ro, Hyuk-Soo Han. Relationship between muscle activation and sagittal knee joint biomechanics in patients with patellofemoral pain syndrome: a cross-sectional study. Knee Surgery & Related Research (2025). DOI: 10.1186/s43019-025-00259-4. © The Author(s) 2025
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Original Figure Legend
Kinetic, kinematic, and EMG data. All curves represent the mean values of biomechanical features at the point of the gait …

Participants and Methods

The study included 31 patients with PFPS and 28 asymptomatic controls. Gait analysis and EMG of VM, VL, ST, and GCM were used. The gait cycle was analyzed separately for weight acceptance (0–12%), SLS (13–50%), and swing (51–100%).

The order in which you read the painting.

Blue lines show control-group means and red lines show PFPS-group means across the gait cycle. Angles, knee-extension moments, and EMG from four muscles are aligned on the same time axis. This cross-sectional comparison included 31 patients and 28 controls. Lower knee-extension moment during weight acceptance and greater semitendinosus activation are interpreted as possible compensatory load regulation. Greater activation does not mean stronger muscles, and this figure alone cannot justify prescribing isolated training of a particular muscle.

Main Findings

The PFPS group had lower knee-extension moment during weight acceptance, without a significant flexion-angle difference. ST activity was higher throughout gait. At KEM <−1% or >5% BW × height, the slopes of increasing VM, VL and ST activation were greater in PFPS.

The point of reading on surgery

These findings provide a basis for considering neuromuscular compensation patterns associated with PFJ pain in rehabilitation research.

Limitations

This is a cross-sectional comparison. The compensatory mechanism is an interpretation, not proof of causality. Rehabilitation and surgical interventions were not compared.

Let's put it briefly.

What did this study confirm?

The PFPS group had lower knee-extension moment during weight acceptance, without a significant difference in flexion angle. ST activity was higher throughout gait.

Can it be applied directly to individual patients' treatment decisions?

This is a cross-sectional comparison. The compensatory mechanism is an interpretation, not proof of causality. Rehabilitation and surgical interventions were not compared.

Keywords

Electromyography
Gait analysis
Patellofemoral pain syndrome
PFJ
patellofemoral pain
gait
EMG

Abstract · Original text

Byung Sun Choi, Soon Bin Kwon, Sehyeon Jeon, Myeongjun Kim, Yunseo Ku, Du Hyun Ro, Hyuk-Soo Han. Relationship between muscle activation and sagittal knee joint biomechanics in patients with patellofemoral pain syndrome: a cross-sectional study. Knee surgery & related research. 2025;37(1):7. doi:10.1186/s43019-025-00259-4.

BACKGROUND

Patellofemoral pain syndrome (PFPS) is one of the most common conditions affecting the knee joint, yet its pathomechanics remain unclear. The aim of this study was to investigate changes in muscle activation and gait patterns and to analyze the relationship between muscle activation and kinetic gait patterns in patients with PFPS.

METHODS

This study included 31 patients with PFPS and 28 healthy volunteers without any symptoms. The sagittal plane motion of the knee joint, representing primary movement of the knee joint, was evaluated to identify changes in gait patterns. Electromyography (EMG) was used to measure muscle activation of vastus medialis (VM), vastus lateralis (VL), semitendinosus (ST), and gastrocnemius (GCM) muscles during gait analysis. Biomechanical features were analyzed during the three phases of the gait cycle; weight acceptance (WA), single limb support (SLS), and swing limb advancement (SLA) (0 ~ 12%, 13 ~ 50%, and 51 ~ 100% of the gait cycle, respectively).

RESULTS

The average knee extension moment (KEM) during WA was lower in the patient group and no significant differences were observed in the knee flexion angle (KFA). With respect to muscle activation, the patient group showed significantly higher muscle activation of the ST muscle in all phases. As the absolute value of the moment increased, the activation of the VM, VL, and ST muscles increased more rapidly in the patient group, especially when KEM was under -1% body weight × height (Bw × Ht) or over 5% Bw × Ht.

CONCLUSIONS

Patients with PFPS exhibit elevated muscle activation, particularly in response to changes in the knee extension moment, which is likely a compensatory mechanism to manage knee joint loading during gait. These results highlight altered neuromuscular adaptations in PFPS, suggesting targeted therapies may help improve functional outcomes. Level of evidence III, cross-sectional study.

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The original paper.

Relationship between muscle activation and sagittal knee joint biomechanics in patients with patellofemoral pain syndrome: a cross-sectional study

Byung Sun Choi, Soon Bin Kwon, Sehyeon Jeon, Myeongjun Kim, Yunseo Ku, Du Hyun Ro, Hyuk-Soo Han
Knee Surgery & Related Research · 2025

DOI · 10.1186/s43019-025-00259-4 PubMed Based data

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Fig. 1 is the original.