Date of Award
Doctor of Physical Therapy (DPT)
The sit-to-stand (STS) task is a fundamental activity of daily living. Although typically considered simple, the task becomes notably more difficult as older adults become affected by age-related physiological and functional declines. Although many studies investigated older adults achieve STS task in certain movement strategies compared to young adults, the underlying mechanisms of why they use different movement strategies are not well established. Therefore, it is crucial to examine underlying mechanisms behind the specific strategies adopted by older adults and to identify the limiting factors that determine altered STS coordination strategies. The purpose of this dissertation was to investigate coordination strategies, neuromuscular capacities, and reserves in older and young adults during the STS task. Healthy older and young adults performed self-selected speed STS task, while three-dimensional movement, ground reaction forces were collected with motion capture cameras, force plates, respectively. Additionally, isometric muscle strength was measured with a Biodex isokinetic dynamometer. The first study used induced acceleration analysis (IAA) to identify lower limb net joint moment contributions to the vertical and horizontal velocities of the body’s center-of-mass (COM). The second study used a regression-based model to estimate maximum potential net joint moment capacities during STS task. Relative muscular efforts (RME) were calculated as the ratio between the inverse dynamics NJMs and the maximal potential NJMs. The third study used hierarchical clustering analysis (HCA) to the biomechanical STS and muscle strength data to identify subgroups with distinct movement strategies. The key findings of this dissertation were that 1) regardless of the joints, NJM contributions to the vertical COM velocity were greater in older than young adults during the momentum transfer phase. However, NJM contributions to the horizontal COM velocity were similar. 2) Knee and hip extensors RME did not show significant differences between age groups. However, older adults altered strategies to reduce mechanical demands on the knee and hip extensors to compensate for their limited ability to generate maximum moment-producing capacities. 3) Four clusters were classified by using the HCA. One of these clusters had a higher proportion of older adults, and their STS coordination patterns were distinguished based on strength deficits.
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