Knee extension moment arm variations relate to mechanical function in walking and running

Area of Science:

• Biomechanics
• Human Movement Science
• Orthopedics

Background:

• The patellofemoral joint is vital for knee extensor function during locomotion.
• Understanding moment arm variation is crucial for explaining biomechanical differences between walking and running.

Purpose of the Study:

• To investigate the knee extension moment arm during walking and running.
• To analyze the influence of knee flexion, motion direction, and inter-subject variability on the moment arm.

Main Methods:

• Utilized a data-driven musculoskeletal model with a 12-degree-of-freedom knee.
• Employed a geometric method to calculate the knee extension moment arm during simulated walking and running.

Main Results:

• Moment arms were smaller during running compared to walking, particularly in the swing phase.
• Knee flexion alters moment arms by shifting the tibiofemoral rotation axis and patella articulation.
• Moment arm variation was influenced by motion direction and inter-subject differences, notably out-of-plane motion.

Conclusions:

• Shorter moment arms during running may enhance the knee's effective mechanical advantage, potentially contributing to higher running velocities.
• Knee motion direction and individual variations significantly affect patellofemoral mechanics during gait.