Background
Physical activity plays an important role in aligning the internal circadian rhythm with the external day-night rhythm, and has been proposed to exert beneficial effects on sleep. We examined if the amount and timing of moderate-to-vigorous physical activity (MVPA) was associated with sleep quality and duration in the general population.

Methods
In this cross-sectional analysis of the Netherlands Epidemiology of Obesity study, physical activity was measured with accelerometery for 4 days, and categorized in performing most MVPA (>5% difference in MVPA) in the morning (06:00-12:00), afternoon (12:00-18:00), evening (18:00-00:00), or with an even distribution of MVPA over the day. Sleep characteristics were reported with the Pittsburgh Sleep Quality Index and dichotomized as good (reference) or poor. We estimated odds ratios of poor sleep with 95% confidence intervals using logistic regression analysis, adjusted for confounding (e.g age, sex, BMI).

Results
We analysed 739 participants (56% women), with a mean (SD) age of 56 (6) years and BMI 26.1 (4.2)kg/m²; 20% performed most MVPA in the morning, 61% in the afternoon, 7% in the evening, and 12% evenly divided their MVPA over the day. The amount and timing of MVPA were not related to sleep quality, latency, duration, efficiency, and medication use, albeit with wide confidence intervals. The amount of MVPA was associated with a lower odds of fatigue-related dysfunction during daytime (OR: 0.54, 95% CI: 0.32-0.94 per hour of MVPA/day). Participants who performed most MVPA in the morning were less likely to experience sleep disturbances (0.23, 0.09-0.60) than participants with an even distribution of MVPA over the day.

Conclusion
These results suggest that the amount of MVPA is associated with functioning during daytime, whereas most MVPA in the morning was associated with less sleep disturbances. Larger studies need to verify these results.