Subject-specific musculoskeletal parameters of wrist flexors and extensors estimated by an EMG-driven musculoskeletal model.

An EMG-driven musculoskeletal model is implemented to estimate subject-specific musculoskeletal parameters such as the optimal physiological muscle length, the tendon slack length and the maximum isometric muscle force of flexor and extensor muscle groups crossing the wrist, as well as biomechanical indexes to quantify the muscle operating range, the stiffness of the musculotendon actuators, and the contribution of the muscle fibres to the joint moment. Twelve healthy subjects (11 males and 1 female, mean age 31.1±8.7 years) were instructed to perform isometric maximum voluntary contractions of wrist flexors and extensors. Recorded EMGs were used as input to the model and the root mean square error (RMSE) between measured and predicted torque was minimised to estimate the subject-specific musculotendon parameters. The model was validated and the RMSE and the normalised RMSE calculated during estimation and validation phases are compared. Estimated subject-specific musculoskeletal parameters vary in a physiological range, while the biomechanical indexes are in agreement with previously published data. The proposed methodology proved to be effective for the in vivo estimation of physiological parameters of the musculotendon complex and has potential as an investigative tool to distinguish aetiological differences among subjects affected by musculoskeletal disorders.