Continuous Volitional Control of a Bionic Leg Supports Diverse Walking Patterns in both AMI and Bone-Anchored Prosthesis User

Myoelectric control paradigms have the potential to enable continuous volitional control of bionic limbs in various movement conditions. Although individuals with agonist-antagonist muscle interface (AMI) amputation were proven to display a greater degree of continuous volitional control in bionic ankle-foot systems with respect to conventional socket-suspended prosthetic users, it remains unclear how myoelectric interfaces could translate to non-AMI prosthetic users with bone-anchored prostheses (BAP). This study proposes a human-machine interface (HMI) based on a neuromechanical model to enable volitional, continuous control of a bionic leg in AMI and BAP users, walking across various speeds and ground inclinations. Differently from state of the art solutions, the proposed method is based on a digital twin of the intact contralateral leg, synthesizing the user's phantom limb musculoskeletal function as controlled by muscle activations measured from the stump. When embedded in a real-time framework, it enabled the participants to achieve volitional modulation of peak muscle activation timing and amplitude during overground walking at three speeds (between 1.6 and 3.96 km/h). Moreover, case studies are provided during calf-raises (30, 45, and 60 bpm) and ramp ascent walking (3 and 5 \% incline). Before prosthesis control tests, the participants underwent a 2-day gait training session; results showed that all three subjects learned how to alter initial muscle activation patterns so that an average of 87\% of peak activation timing fell within target ranges. The proposed neuromechanical modeling technology opens new avenues toward generalizable HMI for the volitional control of active prostheses beyond set conditions and subjects.