This thesis is comprised of two studies on a hybrid forward and inverse dynamic approach to EMG-driven modelling. The focus is placed on application of the presented model to gait of healthy and neurologically impaired subjects and on the expansion of the model to include two joints.

The first chapter describes a biomechanical model of the forces about the ankle joint applicable to both unimpaired and neurologically impaired subjects. EMGs and joint kinematics are used as inputs and muscle forces are the outputs. A hybrid modelling approach that uses both forward and inverse dynamics is employed and physiological parameters for the model are tuned for each subject using optimization procedures. The forward dynamics part of the model takes muscle activation and uses Hill-type models of muscle contraction dynamics to estimate muscle forces and the corresponding joint moments. Inverse dynamics is used to calibrate the forward dynamics model predictions of joint moments. The first chapter describes how to implement an EMG-driven hybrid forward and inverse dynamics model of the ankle that can be used in healthy and neurologically impaired people.

The second chapter investigates biarticular muscles and their role in EMG-driven models in a more comprehensive fashion than previously published, accounting for their contributions of both joints they span. EMG-driven models of the ankle, knee, and ankle and knee combined were developed to compare the estimated joint moments and muscle forces. The models were tuned to a walking trial, and then used to predict walking, hopping, and hop-and-stop trials. Results revealed consistency in predictive ability of all the models, and compared well to the inverse dynamic joint moments for normal gait. The muscle force estimations showed no significant differences in most muscles that span only one of the joints studied. However, the gastrocnemii, which span the ankle and knee, gave significantly different muscle force results.

This thesis will show that EMG-driven models can be used for healthy and neurologically impaired gait, and that single-joint models that include biarticular muscles will need to account for the roles of those muscles at other joints to obtain the same results as more complex and, presumably more physiologically realistic, multi-joint models.