Torque Validation of a Single-Joint Ankle Dynamometer: An evaluation framework using force plate and pressure insole data

This study aims to evaluate the validity and reliability of torque output from a prototyped single-joint ankle dynamometer. A torque validation framework was developed using ground reaction forces (GRFs) recorded by a force plate, and the centre of pressure (CoP) from a pressure insole. Experimental testing was performed with one single test subject, where both plantarflexion and dorsiflexion were assessed when performing isometric and isokinetic trials. The torque was estimated by transforming the GRF vectors measured by a force plate into a local coordinate system fixed on the dynamometer as well as calculating the moment arm between the ankle joint and the CoP. This externally calculated torque was later compared to the torque from the dynamometer's own load cell. Results showed that the shape of the GRF-based torque was in general alignment with the load cell torque, but with a consistently lower magnitude. Additional analysis using the normal force recorded by the pressure insole to estimate the torque proved to be closer in magnitude to the load cell torque, suggesting potential errors in the transformation or recording of GRFs. This study thus provides a foundation for further refinements of the validation framework as well as highlighting possible improvements for future work.