Inter relationships among objectively measured physical activity, sleep and time outdoors

Purpose: Increasing physical activity (PA) may be an important non-pharmacological approach to improve sleep quality but it is not clear how level and timing and co-current light exposure influence sleep quality. PA time outdoors may be more beneficial for sleep, but only recently has it been possible to measure sleep, physical activity, and outdoor time objectively in large-scale studies.

Methods: 350 older adult women (mean age = 55.38 ±9.89 yrs; mean BMI = 27.74 ±6.12) were recruited from different regions of the US. Participants wore a GPS device and an ActiGraph GT3X+ accelerometer on the hip and wrist, for 7 days and 7 nights. Daily minutes in moderate-to-vigorous PA (MVPA) were computed from the hip device, total minutes sleep time (TST) and sleep efficiency (SE) were computed from the wrist device, and time spent outdoors was calculated from GPS using the satellite to device signal-to-noise ratio. A generalized mixed-effect model was used to assess temporal associations between MVPA and sleep at the daily level within individuals.

Results: An increase in daily MVPA was associated with a decrease in TST (β= -0.11, p<0.05) and an increase in SE (β= 0.999, p< 0.05), adjusting for age and BMI. Time spent outdoors was not a significant predictor of sleep duration or efficiency.

Conclusions: These preliminary data support acute effects of MVPA on sleep duration and efficiency. Although absolute time spent outdoors did not influence these relationships, further research is needed to discern effects of specific outdoor activities and light exposure.