Ankle impedance reliability

In this project, I explored how reliably we can measure the mechanical impedance of the ankle during standing and walking. We used a custom-built robotic platform and motion capture setup, and measured the ankle torque and angle response to small perturbations (example perturbation shown in gif above). The goal was evaluating how reliably we can measure impedance parameters such as stiffness, damping and inertia, as an accurate and reliable measurement can help as a clinical metric as well as to develop biomimetic prostheses and exoskeletons.

To gather the data, we had 18 participants come to the lab. Participants underwent standing and walking trials where perturbations were applied to their ankles. In standing trials, the perturbations were applied while participants remained stationary, while during walking trials, the perturbations were timed to specific phases of the gait cycle. Using the recorded torque and angle responses, we calculated stiffness, viscosity, and inertia by fitting a second-order parametric model.

To calculate the reliability of these measurements, we had participants come in on two three-hour sessions: Test and Restest. This allowed us to determine the test-retest reliability and minimal detectable change (MDC) for each parameter. Additionally, we investigated factors like gait phase and the impact of including or removing the robot’s inertia on the consistency of the results.

Our findings showed that stiffness and viscosity parameters are highly reliable, making them valuable for clinical assessments and in designing advanced assistive devices like biomimetic prostheses and exoskeletons. This work contributes to the growing body of knowledge needed to translate such measurements into real-world applications.

If you’re interested in learning more, you can read the full paper, published in the Journal of Gait and Posture and available here.