Ankle Mechanical Impedance During the Stance Phase of Running.

Objective: Differences in locomotor biomechanics between walking and running provide fundamental information about human ambulation. Joint mechanical impedance is a biomechanical property that governs the body's instantaneous response to disturbances, and is important for stability and energy transfer. Ankle impedance has been characterized during walking, but little is known about how humans alter joint impedance during running. The purpose of this study was to estimate ankle impedance during the stance phase of running, and compare to previously reported estimates during walking.

Methods: Perturbations were applied to the ankle using a one-degree-of-freedom (DOF) mechatronic platform. Least-squares system identification was performed using a parametric model consisting of stiffness, damping, and inertia.

Results: The model accounted for 89% ± 16% of variance. Ankle stiffness reached a maximum of 10 Nm/rad/kg at the end of mid-stance, decreasing in terminal stance phase to values previously reported during swing phase. Quasi-stiffness values differed significantly from stiffness across the stance phase of running. Comparing ankle impedance estimates between walking and running showed differences in both magnitude, and temporal variation.

Conclusion: Ankle impedance differs significantly between walking and running. Significance: This study provides novel information about the biomechanics of running and broadens our understanding of how the mechanical impedance of the ankle joint differs between locomotor tasks, motivating the need for future studies.