Dynamics of Quadriceps Muscles during Isometric Contractions: Velocity-Encoded Phase Contrast MRI Study

Area of Science:

• Biomechanics
• Human Physiology
• Musculoskeletal Imaging

Background:

• Understanding quadriceps muscle function during voluntary contraction is crucial for biomechanical analysis.
• Spatial heterogeneity in muscle displacement may influence force transmission and joint mechanics.

Purpose of the Study:

• To quantify the spatial heterogeneity of muscle displacement within and between quadriceps compartments during isometric contraction.
• To investigate the dynamic behavior of vastus lateralis (VL), vastus medialis (VM), vastus intermedius (VI), and rectus femoris (RF) muscles.

Main Methods:

• Utilized velocity-encoded phase contrast MRI to image thigh muscles of seven subjects during isometric knee extensions.
• Acquired dynamic images at proximal, middle, and distal locations, calculating displacement via a tracking algorithm.
• Analyzed displacement along three orthogonal axes (X, Y, Z) for each of the four quadriceps compartments.

Main Results:

• Muscle tissue displacement was nonuniform within axial sections and across longitudinal locations.
• Vastus medialis (VM) showed significantly larger displacement at the middle location, and vastus intermedius (VI) at the distal location.
• Vastus intermedius (VI) exhibited significantly larger Z-axis displacement (aligned with force) across all locations; displacements over 20 mm occurred near central aponeuroses.

Conclusions:

• Quadriceps muscles operate as a functional unit, transmitting force through central aponeuroses.
• Despite complex individual muscle behaviors, the quadriceps collectively generate force, reflecting diverse physiological characteristics and architectures.