Thesis (M.S.M.) PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / BACKGROUND/PURPOSE: Gait speed and walking endurance are measures of performance and overall health in older adults; however it is unclear whether measuring both provides additional clinically useful information over measuring just one. The purpose of this study is to systematically explore the co-variation of trajectories of speed and endurance over 8 years in healthy older adults, and to examine the association of knee extensor strength and cardiorespiratory impairment with distinct trajectories. Understanding such trajectories and their determinants will help clarify the utility of testing each outcome separately. METHODS: Data were obtained prospectively in a subset of the Health, Aging and Body Composition study (Health ABC), which included 2364 initially well-functioning men and women 70 to 79 years of age. Gait speed was determined from a 20-meter walk. Walking endurance was measured from a two-minute walk. The dual trajectories of gait speed and walking endurance were estimated using a group-based mixture model using SAS macro “PROC TRAJ”. The procedure calculates the probabilities of trajectory group membership for gait speed membership conditioning on walking endurance groups and vice versa. We also examined the association of knee extensor strength and cardiorespiratory impairment with distinctive trajectories adjusting for age, sex, and body mass index (BMI). RESULTS: We identified four gait speed trajectories and three walking endurance trajectories. Older adults with the greatest decline in gait speed and walking endurance slowed 0.032 m/s and 0.025 m/s per year, respectively. There was high correlation between gait speed and walking endurance trajectories, r= 0.84, p<0.0001. Less knee extensor strength and the presence of cardiorespiratory impairment were associated with membership in worse gait speed and walking endurance trajectories. After adjustment for walking endurance trajectories, only knee extensor strength was associated with worse gait speed trajectories. After adjustment for gait speed trajectories, both strength and cardiorespiratory impairments continued to be associated with walking endurance trajectories. CONCLUSIONS: There was high convergence of trajectories of gait speed and walking endurance. Therefore, changes in walking endurance can be inferred from measuring gait speed alone. However, cardiorespiratory impairment had a unique association with trajectories of walking endurance, but not gait speed. Therefore, measuring gait speed alone may not provide as much information as measuring walking endurance for those with cardiorespiratory impairment. / 2031-01-01