Delayed sleep timing is associated with low levels of free-living physical activity in normal sleeping adults

Objective and Background: We and others have reported that experimentally induced short sleep does not affect resting metabolic rate and leads to increased laboratory-measured 24-h energy expenditure. Here, we aimed to determine if sleep timing and/or quality are related to physical activity (PA) levels. Methods: Measures of PA via waist actigraphy, sleep diary, and sleep quality questionnaires were collected over a 7-18-day period in 22 adults (mean age +/- standard deviation (SD): 35.8 +/- 4.6 years, and mean body mass index +/- SD: 23.8 +/- 1.1 kg/m(2)) who were on their habitual sleep-wake and activity schedules. Results: During the recording period, mean (+/- SD) bedtime and wake times were 00: 17 +/- 1:07 h (range: 22:02-02: 07 h) and 08: 20 +/- 1: 14 h (range: 06:30-10:11 h), respectively. After controlling for sleep duration, later bedtime, wake time, and midpoint of sleep were associated with less time spent in moderate-to-vigorous PA (p = 0.013, p = 0.005, and p = 0.007, respectively), and increased time in sedentary PA (p = 0.016, p = 0.013, and p = 0.013, respectively). Conclusions: Current results suggest that even relatively small alterations in sleep timing may influence PA. However, causality cannot be inferred from this cross-sectional study. Clinical intervention studies should be conducted to assess the relationship between sleep timing and energy balance. (C) 2014 Elsevier B.V. All rights reserved.