Optimization of a Synergy-Driven Musculoskeletal Model to Estimate Muscle Excitations and Joint Moments of the Ankle Joint at Different Walking Speeds

Control frameworks of powered prostheses should be fine-tuned to user-specific requirements as well as adaptable to different movement conditions, in order to be adopted as a beneficial solution. Otherwise, the lack of support from the prosthesis might lead to the adoption of inappropriate postures while walking and standing. The objective of the current study is to optimize a generic synergy model of muscle excitations to fit subject-specific torque at the ankle joint through a scaled musculoskeletal model across various speeds. The synergy optimization framework developed in this study was based on an interior point optimizer (IPOPT) combined with direct collocation. The framework was validated by comparing resultant moments from inverse dynamics with computed torques. Results show that the model is able to reproduce the ankle moment of six subjects at six different speeds (RMSE $0.1277 ± 0.02$). We propose the current solution as an accurate method of personalizing control framework for powered prostheses across different walking conditions.