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The complexity of the human musculoskeletal system presents challenges in accurately identifying its characteristics, particularly due to the presence of redundant actuators on a single joint. Non-invasive measures are necessary to overcome these challenges. Optimization algorithms have emerged as a crucial tool to advance subject-specific musculoskeletal modeling allows a more realistic representation of biomechanical behaviors, enhancing our understanding of human movement and enabling better clinical decision-making. Furthermore, optimization algorithms play a vital role in customizing rehabilitation and assistive devices, such as orthoses and prostheses. The current ankle-foot orthosis (AFO) stiffness measurement methods require bulky, complex designs, and often permanent modification of the AFO. To address this, we proposed the Ankle Assistive Device Stiffness (AADS) test method, which utilizes a simple design jig and motion capture system. In our method we employed a static optimization algorithm to estimate external forces and AFO torque, providing reliable stiffness quantification. The AADS test demonstrated high precision among different operators and trials, with an overall percent error within ±6%. In the pursuit of accurately measuring muscle-tendon parameters, various techniques, including shear waves, have been utilized. However, these techniques often are invasive or lack the ability to provide quantitative measurements. In our second study, we introduced a noninvasive method for estimating passive muscle-tendon parameters (PMPs) in knee flexors/extensors and the Achilles tendon. We employed a direct collocated optimal control algorithm and evaluated the precision of the proposed method through simulation, replica leg experiments, and in-vivo experiments involving 10 subjects. The estimated range for tendon slack length was reported between 0.59 and 1.13, while the median of tendon stiffness was 421 KN/m. Muscle stiffness ranged between 473 N/m and 1200 N/m. The average root mean square error (RMSE) between experimentally collected joint kinematics and kinetics and forward dynamic verification was less than 0.56° and 12 mN.m/Kg, respectively.

Stress fractures are common overuse injuries that have plagued athletes for many years. Often referred to as fatigue fractures, they are formed when the skeletal muscles fatigue and can no longer absorb the shock of repetitive pounding activities such as running. Stress fractures are most common in the weight-bearing bones of the lower extremities and are usually preceded by sudden increases or changes in training routines. Because they are most common in athletes who are least fit, it has been hypothesized that freshmen athletes who are not prepared for the increased physical demands of college athletics have the greatest risk for developing stress fractures compared to other academic classes. As of yet however, there have been very few studies that have examined the interaction of different variables such as academic class, on the formation of stress fractures. Therefore, the purpose of this study was to look at the incidence, frequency and pattern of stress fractures among the female athletes at Virginia Polytechnic Institute and State University. A retrospective analysis of 28 injury cases over four years revealed that 67% of the injuries occurred in freshmen athletes. The majority of these were in the lower leg and occurred in mid-season rather than pre-season. There were no relationships found between the variables sport, class, site and season and thus it was concluded that the incidence of injury was not affected by the interaction of these variables. However, the variables themselves did influence the formation of stress fractures. Ultimately, this study provided insight on what factors should be carefully examined in order to prevent future stress fracture injuries in collegiate athletes. / Master of Science

Thesis (M.D.) -- University of Texas Southwestern Medical Center at Dallas, 2007. / Vita. Bibliography: pp.73-78.

Thesis (Ph. D.)--University of Texas Health Science Center at Houston, School of Public Health, 2007. / "August 2007." Advisor: Benjamin C. Amick, III. Includes bibliographical references.

Thesis (doctoral)--Göteborg University, 1994. / Added t.p. with thesis statement inserted.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 131-154).

Thesis (M.P.H.)--Southern Connecticut State University, 1998. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.