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ISB Dissertation Award Funds Report

Michelle Heller

Thank you for selecting me to receive the ISB Dissertation Award for my work regarding in-shoe orthoses and their effects on gait kinematics and kinetics. The funds have been used to purchase needed supplies for the gait lab portion of the study involving human subjects. They have also been used to purchase strain gauge rosettes, axial strain gauges, a fine-tipped soldering iron, and other items required to measure strain within the bones of cadaveric lower limbs. Your financial support is very much appreciated, and I look forward to continuing my participation in the International Society of Biomechanics in future years.


ISB Dissertation Award Report

Michelle Heller

Stress fractures in the lower limbs affect 5% to 20% of military recruits, which contributes to decreased military readiness and increased medical costs. Lower extremity mechanics could play a role in stress fracture development, and in-shoe orthoses may serve as a preventative measure. We hypothesized that the use of in-shoe orthoses would alter gait kinematics and kinetics during jogging. We also hypothesized that carrying an external weight would alter walking kinematics and kinetics. Fifty-three female subjects with no history of major musculoskeletal injuries participated in the study. Each subject’s foot type was classified as rigid, normal, or flexible by means of a navicular drop test. Reflective marker clusters were attached to each subject’s pelvis, thighs, calves, and shoes, and a six-camera motion analysis system (Eagle, Motion Analysis, Santa Rosa, CA) collected marker data at 200 Hz and analog force platform (Kistler Instrument Corp., Switzerland) data at 1000 Hz. The subjects walked and jogged in laboratory-issued New Balance 609 cross-trainers under four different posting conditions: shoe only, shoe with insole, insole with lateral posting, and insole with medial posting. They also walked while carrying a standard military pack with a gross mass of 18.1 kg. In addition to the motion portions of the study, the subjects each stood on the Kistler force platform for thirty seconds as part of an investigation into how a heavy external load affects postural stability. Based on a significance level of a = 0.05, the orthotic conditions had a significant effect on peak hip abduction, ankle inversion, ankle external rotation, ankle internal rotation, and ankle range of motion (external/internal rotation), but had no effect on the peak ground reaction forces. The backpack affected peak hip abduction, hip range of motion (abduction/adduction), hip external rotation, hip flexion, hip range of motion (flexion/extension), knee external rotation, ankle range of motion (eversion/inversion), ankle dorsiflexion, ankle plantarflexion, and ankle range of motion (dorsi/plantarflexion). In addition, the backpack significantly affected the ground reaction forces in all directions. Backpack carriage decreased postural stability as was evidenced by increased center of pressure (COP) path length, COP area, medial-lateral excursion, and anterior-posterior excursion. Another finding was that hindfoot flexibility had a significant effect on gait kinematics and kinetics, as was evidenced across both the orthoses and backpack conditions. These results have shown that wearing in-shoe orthoses can affect a person’s gait and that wearing a heavy backpack can affect both a person’s gait and postural stability.