Shoulder musculoskeletal modeling: from data-tracking to predictive simulations

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My long-term objective is to simulate biofidelic and optimal upper-limb movements to improve shoulder function or reduce risk factors for shoulder disorders. In biomechanics, internal loads (muscle-tendon and joint forces) are essential for understanding how humans move and for predicting functional outcome. Such loads can be estimated using neuro-musculoskeletal [NMSK] models. However, muscle redundancy remains an unsolved problem in NMSK modeling. The originality of our approach has been to track simultaneously EMG and skin markers to estimate the internal loads. It is promising, not only for data-tracking simulations, but also for predictive simulations (i.e. generating optimal and biofidelic movements, without experimental data). However, major obstacles remain for technology translation to clinical/ergonomic applications; the major ones correspond to my specific objectives: SO1) Provide real-time biofeedback of internal loads using an online NMSK data-tracking simulation; SO2) Identify participant-specific muscle-tendon properties; SO3) Transfer data-tracking algorithm to predictive simulations with inclusion of motor control theories (muscle synergies and the kinematic theory). SO1) To speed-up the optimization process and provide feedback to patients and clinical, the optimal control problem will be expressed as a nonlinear moving horizon estimator (with 50-100 ms time span) with enhanced convergence due to fewer variables. Since not all EMGs can be systematically measured, missing EMG will be inferred using a long short-term memory neural network from data taken on a population (n=30) performing various tasks. SO2) To personalize muscle-tendon properties, students will first focus on the identification of maximal isometric muscle forces, optimal lengths, and nonlinear shape factors between EMG and neural excitation using series of (sub)maximal efforts performed on an isokinetic dynamometer. Identification algorithms from systems biology will be adapted to NMSK models. SO3) Muscle synergies will be first extracted from our large EMG database. Use of synergies will reduce the control space and could enforce biofidelic patterns of muscle excitations (e.g. to replicate the co-contraction for glenohumeral joint stability). Moreover, the velocity of the hand will be constrained according to the kinematic theory to guide the optimization toward realistic solutions. The optimal solutions will be validated using previously-collected movements to determine the most relevant objective functions, constraints and motor control theories for generating realistic movements. My Discovery Program proposal will support 4 PhD and 10 undergraduate students who will be trained on advanced musculoskeletal biomechanics modelling in a multidisciplinary environment and state-of-the art infrastructure. Our ground-breaking algorithms will be the foundation of clinical, sports, artistic and ergonomic applications.