Abstract
PURPOSE: Sedentary behavior is associated with poor physical function in older adults, which can lead to accelerated skeletal muscle aging (sarcopenia) and premature mortality. We examined the independent and joint effects of sedentary behavior and moderate to vigorous intensity physical activity (MVPA) with measures of physical functioning. METHODS: We studied 5408 participants in the REasons for Geographic and Racial Differences in Stroke study who wore a hip-mounted accelerometer over seven consecutive days (2009-2013) and had self-reported and directly observed physical function (time walk, chair stand test) measured during an in-home visit conducted from 2013 to 2016. RESULTS: Greater sedentary time was significantly associated with poorer chair stand and timed walk scores. Substituting 30 min of sedentary time with 30 min of MVPA was associated with significant improvements in chair stands (β -0.57; P = 0.007) and timed walk (β -0.36; P = 0.01). Similar, but less robust, findings were observed for reallocations of sedentary time to light-intensity physical activity. In joint association analyses, high sedentary time in combination with low MVPA (but not in combination with high MVPA) was associated with poorer physical function compared with the referent group (low sedentary time/high MVPA; P < 0.001 for all). CONCLUSIONS: Greater time spent being sedentary was associated with worse physical functioning outcomes. However, reallocations of sedentary time to light-intensity physical activity, and especially MVPA, were associated with more favorable physical functioning. Interventions aimed to increase MVPA and reduce sedentary behavior should be a priority, especially among populations at greatest risk for sarcopenia and physical function decline.