Physical activity is a well-known protective factor against poorer mental health outcomes. Feelings of depression, social isolation, and stress have increased since the onset of the COVID-19 pandemic. Public health measures implemented to mitigate the spread of the virus have had some unintended consequences on older adults’ physical and mental health. Researchers and government officials recommend physical activity to minimize the negative psychological and physiological impacts of COVID-19. However, older adults have generally shown less moderate-to-vigorous physical activity and positive behavioural adaptations during the COVID-19 pandemic, highlighting a need for physical activity programs and strategies targeted for older adults. Filling this gap, the current study developed and implemented a remote exercise training program for older adults. Employing a measurement burst design with repeated ecological momentary assessments, the current longitudinal randomized control study examined the dynamic relationships of physical activity, depressive symptoms, social isolation, and COVID-19 related stress in older adults. The results from multilevel model analyses showed: (1) the exercise training program was effective in increasing physical activity; (2) sex, age, and group assignment were significant predictors of physical activity; (3) physical activity did not reduce depressive symptoms over time; (4) social isolation is directly associated with depressive symptoms; and (5) COVID-19 stress is inversely associated with depressive symptoms. At-home physical activity programming could be an effective way to increase physical activity among older adults; thus, more research into at-home physical activity programs is needed. / Graduate