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

• We examined how sleep timing is related to physical activity levels in adults.
• Sleep and physical activity were tracked for 1–2 weeks under free-living conditions.
• Later sleep timing was associated with less vigorous and more sedentary activity.

Objective and BackgroundWe 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.MethodsMeasures 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/m2) who were on their habitual sleep–wake and activity schedules.ResultsDuring 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).ConclusionsCurrent 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.