Integrating Rehabilitation Knee Orthosis and FES-Feedback System for Isometric Training Protocols

The present work investigates a preliminary case of integration of functional electrical stimulation (FES) and a portable knee orthosis with a built-in dynamometer for rehabilitation protocols. Building upon previous work (Freire, 2024), this updated system aims to enhance user integration, validate structural improvements, and integrate an FES feedback loop with the system's operation. The proposed training orthosis is equipped with biomechanical torque measurement capabilities, allowing execution of isometric knee extension exercises at predefined angles.A closed-loop control approach allows for real-time adaptation of a FES signal based on the user's muscle response and the biomechanical knee torque measured, allowing for adapted training routines. The compact and lightweight design of the system, achieved through the use of 3D-printed parts and low-cost commercial components, along with a simplified control system, enhances portability and user comfort.Experimental trials were performed with a non-impaired subject demonstrated successful integration between the systems, with the structural part of the orthosis withstanding significant levels of mechanical stresses along with a robust response of the embedded and feedback systems. The test trials evaluated three different levels of FES-induced contractions (40 mA, 42 mA and 44 mA) for 30s, where higher FES currents resulted in increased torque production and shorter response times. However, fatigue onset was observed earlier with higher currents, likely due to increased metabolic demand and fiber recruitment. These findings highlight the importance of optimizing stimulation parameters and considering fatigue in future studies.This work's findings show that the integrated system, with future work modifications, may be able to improve rehabilitation protocols for individuals with lower limb impairments, while also potentially offering a valuable tool for mid-tier strength training in healthy individuals.