The effect of including a subtalar joint in a dynamic musculoskeletal model has not been fully explored or validated. The subtalar joint is often modeled as a one DOF hinge with the tri-planar axis defined as a combination of inclination and deviation angles measured from the ground and midline of the foot, respectively. The overall purposes of this dissertation were to explore how the inclusion of the subtalar joint and the definition of origin location and axis orientation affect the kinematics, joint kinetics, and muscle activations of the knee, ankle, and subtalar joint during dynamic tasks of walking and running through sensitivity analyses and validation using OpenSim (SimTK, Stanford, CA).
The findings of this dissertation conclude that if the subtalar joint is to be included in a model, the location of the axis origin needs to be considered and accurately defined, especially if the inclination/deviation angles of the rotational axis will be modified to represent a more subject-specific definition. The models in this study were validated for walking using available in vivo joint contact data from the Grand Knee Challenge. Further inferences were made on the validity of the models for running based on similarities seen in the EMG and muscle activation patterns. The conclusions from this work are drawn from analysis of walking and running, which are primarily sagittal plane motions. Future studies analyzing more complex motion such as cutting or walking on uneven terrain, where there is more transverse and coronal plane motion, may further highlight the importance of the subtalar joint in musculoskeletal modeling as it plays a more active role during foot adaption
