Knee Muscle Activity: Frontal Plane

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Introduction

0% · Heel strike

Side view · posterior muscles
Vasti (VM · VL · VI deep, dashed)
Active — contributes to stabilityBiceps femoris (side view)
Active — contributes to stabilityGastrocnemius (side view)
Schematic muscle activity (relative scale)

Vasti, biceps femoris and gastrocnemius; schematic activation

+ Increasing activity− Not plotted

Schematic relative amplitude; not measured values.

Schematic muscle activity00%20%40%60%80%100%
Gait cycle: 0%

Heel strikeCoactivation supports knee stability.

Graph explanations and references

— Vasti — Biceps femoris — Gastrocnemius
Overall activity timing and contribution to stability, not separately measured frontal-plane activation; heights are not EMG.

Net joint value — does not identify which muscle is active

Internal abduction torque opposes the external adduction load in stance; muscles and passive tissues contribute together. Near zero in swing.

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Chapters
Learning objectives

Relate vasti, biceps femoris and gastrocnemius activity to knee stability against the external adduction torque in stance.

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