Abstract:
This dissertation used both cross-sectional and intervention studies to investigate the implication of childhood obesity on the musculoskeletal system during locomotion. Specifically, it compared the gait biomechanical and energetic differences between obese and normal children. Two different intervention studies (weight loss and muscle strength training) were carried out to investigate the cause-and-effect relationship between body mass, muscle strength and gait strategies. In addition, this study applied subject-specific musculoskeletal modelling and simulation to quantify compressive tibiofemoral force and individual muscle function. These results suggested that the excess body mass plays a dominant role in a larger joint load and greater energy cost in obese children. The obese children preferred to walk at a speed that has minimal energy cost and maximal mechanical efficiency. Weight loss reduced the differences in gait kinetics and energetics between obese and normal weight children, but the change of spatiotemporal gait parameters is not a necessary outcome for a short-term weight loss. By contrast, obese children walked with a faster self-selected speed and a larger hip flexor moment after an eight week strength training program. This finding suggested that lower extremity muscle strengthening improves obese children’s ability to promote locomotion through greater propulsion. However, it may not reverse the impact of excess body weight on natural walking biomechanics and energetics. A further simulation study was carried out to investigate the knee joint reaction force and muscle function in obese children using subject-specific model. The simulation results showed that obese children and normal weight children use similar muscles to support and accelerate body COM, but normal weight children had significantly greater normalized compressive tibiofemoral force and individual muscle contribution to COM. The absolute compressive tibiofemoral force and muscle forces were still greater in obese children. Therefore, the obese child may adapt a compensation gait strategy to avoid increasing compressive tibiofemoral force and muscle requirements during walking.
