Musculoskeletal modeling and marker-based motion capture techniques are commonly used to quantify the motions of body segments, and the forces acting on them during human gait. However, when these techniques are applied to analyze the gait of people with lower limb loss, the clinically relevant interaction between the residual limb and prosthesis socket is typically overlooked. It is known that there is considerable motion and loading at the residuum-socket interface, yet traditional gait analysis techniques do not account for these factors due to the inability to place tracking markers on the residual limb inside of the socket. In the present work, we used a global optimization technique and anatomical constraints to estimate the motion and loading at the residuum-socket interface as part of standard gait analysis procedures. We systematically evaluated a range of parameters related to the residuum-socket interface, such as the number of degrees of freedom, and determined the configuration that yields the best compromise between faithfully tracking experimental marker positions while yielding anatomically realistic residuum-socket kinematics and loads that agree with data from the literature. Application of the present model to gait analysis for people with lower limb loss will deepen our understanding of the biomechanics of walking with a prosthesis, which should facilitate the development of enhanced rehabilitation protocols and improved assistive devices.

Without his patience, guidance, and support this work would not have been possible. I am also grateful to FTL Labs Corp. for their assistance and sponsorship for the project. A big thanks to Damon and Jared from FTL Labs for developing a graphical user interface that aided the thesis work. To my committee members, Andrew LaPrè and Yossi Chait, I am extremely thankful for all the suggestions, critiques and feedback which have played a really important role in shaping the thesis. Last but not the least, I also wish to thank my lab-mates Ericber, Julio, Mark and Vinh who have helped me stay motivated, and whose help and suggestions have been of great assistance.

Simulation of musculoskeletal systems using dynamic optimization is a powerful approach for studying the biomechanics of human movements and can be applied to human-robot interactions. The simulation results of human movements augmented by robotic devices may be used to evaluate and optimize the device design and controller. However, simulations are limited by the accuracy of the models which are usually simplified for computation efficiency. Typically, the powered robotic devices are often modeled as massless, ideal torque actuators that is without mass and internal dynamics, which may have significant impacts on the simulation results. This article investigates the effects of including the mass and internal dynamics of the device in simulations of assisted human movement. The device actuator was modeled in various ways with different detail levels. Dynamic optimization was used to find the muscle activations and actuator commands in motion tracking and predictive simulations. The results showed that while the effects of device mass and inertia can be small, the electrical dynamics of the motor can significantly impact the results. This outcome suggests the importance of using an accurate actuator model in simulations of human movement augmented by assistive devices. Novelty• Demonstrating the effects of including mass and internal dynamics of the actuator in simulations of assisted human movement • A new OpenSim electric motor actuator class to capture the electromechanical dynamics for use in simulation of human movement assisted by powered robotic devices

This paper presents simulations of a new type of powered ankle prosthesis designed to dynamically align the tibia with the ground reaction force (GRF) vector during peak loading. The functional goal is to reduce the moment transferred through the socket to the soft tissue of the residual limb. The forward dynamics simulation results show a reduction in socket moment and the impact on the pelvis and affected-side knee. This work supports further research on transtibial prosthetic designs that are not limited to mimicking physiologically normal joint motions to optimize lower limb amputee gait.