Effect of knee flexion angle on active joint stiffness.

RANGE of motion of joints; JOINT diseases; ANKYLOSIS; KNEE; TORQUE; MUSCLE contraction; MUSCULOSKELETAL system; CLINICAL trials

The purpose of this study was to determine if active joint stiffness measured during maximum voluntary knee extension contractions was affected by knee flexion angle. Eighteen subjects volunteered (11 male, seven female). A stretch was imposed on isometric knee contractions performed at 30°, 50°, 70°, 90°, and 110° of knee flexion. Active joint stiffness was computed from the increase in torque relative to the change in knee flexion angle for the first 50 ms of the stretch (approximately 1.5°) and corrected for effects of gravitational component due to leg mass and passive tension. There was a plateau in knee extension torque between 70° and 90° with lower values at all other angles ( P < 0.05). Peak active joint stiffness occurred at 70° with lower values ( P < 0.05) at all other angles except 50°. Stiffness at 70° (441.1 ± 189.9 Nm rad−1) was 49% higher than at 30° and 45% higher than at 110°. Active joint stiffness was dependent on knee flexion angle. Peak joint stiffness during maximal contractions occurred at, or prior to, the optimal angle for torque production for all subjects. [ABSTRACT FROM AUTHOR]

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