The effects of foot orthotics on the musculoskeletal system is one topic in the area of biomechanics which has attracted some scientific scrutiny without providing any conclusive evidence despite the fact that foot orthotics are used by many recreational runners. The main purposes of this investigation were to quantify the effects of posting and custom-molding of foot orthotics on lower extremity kinematics, kinetics and muscle activity, to determine the relationship between differences in comfort and changes in lower extremity kinematics, kinetics, and muscle activity as a response to foot orthotics, and to determine whether the effects of foot orthotics change over time during running for a specific group of runners.

The results of this study showed that the effects of posting of foot orthotics were different from the effects of custom-molding of foot orthotics and that the effects of custom-molding were dominant when combining posting and custom-molding. Posting and custom-molding of foot orthotics did affect lower extremity kinematics, kinetics, and muscle activity and comfort. The greatest effects were observed in the vertical loading rate. Differences in comfort were related to changes in lower extremity kinematics, kinetics, and muscle activity. Periodic measurements over a three week period yielded consistent results in the measured variables. The information provided in this dissertation contributes to the understanding of the effects of foot orthotic components on the musculoskeletal system during locomotion. This information may be useful in selecting appropriate components of foot orthotics for specific groups of individuals and for physical activities such as running.