Characterization of the ankle dynamic joint stiffness as a function of gait speed for overground and treadmill walking.

The ankle dynamic joint stiffness (DJS), defined as the slope of the joint angle-moment plot, measures the resistance of the ankle joint to movement when the foot is in contact with the ground. DJS helps to stabilize the ankle joint, and its characterization helps to identify gait pathology and assist foot prosthesis design. This study analyzes the available gait dynamics data to obtain ankle DJS parameters for population groups according to age, gender, and gait speed for overground and treadmill walking. This study classified the groups into five walking speeds normalized using the Froude number. Herein, 12 ankle DJS parameters were determined. These include four linear segments: controlled plantar flexion (CP), early response phase (ERP), large response phase (LRP), and descending phase (DP), their corresponding turning points, the net mechanical work, the absorbed work, and the loop direction. Ankle dynamics data for 92 individuals was collected from two gait data repositories. The analysis reveals a notable disparity in stiffness values between overground and treadmill gait. Specifically, the CP stiffness is significantly higher for overground gait. In contrast, the DP stiffness displays an opposing pattern, with higher values observed during treadmill walking. A negative stiffness for LRP was found at fast speeds for all groups. The sorted data, analysis tools, and findings of this study are meant to help practitioners design prosthetic and rehabilitation devices based on age, gender, and walking environment at different gait speeds.