WALK behaviors
napping
Physical activity and sedentary time were measured objectively with actigraphy. Participants wore tri-axial accelerometer (Actigraph GT3X, Actigraph, Pensacola, FL) on the hip using an elastic belt or clip. Data collected at 80 Hz were downloaded (Actilife software, v6.13.3, Actigraph, Pensacola, FL, USA). Activity counts were analyzed at the minute-level from the vertical axis of the device. Classification of activity was determined using cut-points to categorize minutes in sedentary behavior (< 100 counts per minute), light (100–2019 CPM), moderate (2020–5998 CPM), and vigorous physical activity (5999 + CPM) [Physical activity actigraphy data were merged with sleep actigraphy data at the minute-level to determine “daytime” physical activity measures between morning sleep offset and nighttime sleep onset, which identifies true sedentary behavior that does not include nighttime sleep or napping. Physical activity days were determined invalid if there were > 25% non-wear minutes during the “daytime” portion of the day, or if there was < 20 h within the day that was “forced-ended” due to an invalid sleep period. Sleep and physical activity actigraphy temporal alignment and valid day criteria methods are detailed elsewhere [