Author(s): BJÖRNSDOTTIR, K., ARNARDOTTIR, N., GESTSDOTTIR, G., SAEVARSDOTTIR, S., JOHANNSSON, E. , Institution: UNIVERSITY OF AKUREYRI, Country: ICELAND, Abstract-ID: 1933

INTRODUCTION:
Sleep, physical activity (PA), and sedentary behavior (SB) are well-established determinants of overall health and well-being. Regular PA supports both physical and mental health, whereas insufficient sleep and excessive sedentary time are associated with adverse health outcomes. Globally, a large proportion of adults are insufficiently active, and PA levels tend to decline with age. Early adulthood is a demanding and formative life stage, often marked by increasing career and family responsibilities that may shape behavior patterns. However, objective measurements on sleep, PA, and SB during this period are limited, and little is known about how Icelanders in this age group allocate their time. The aim of this study was to describe free-living patterns of sleep, PA, and SB among 36-year-old Icelanders using accelerometers.
METHODS:
This cross-sectional study included 276 ostensibly healthy Icelandic adults (51% female), aged 36 years at the time of data collection (October 2024–June 2025). Eligibility criteria included being born in 1988 and residing permanently in Iceland. Free-living behavior patterns were assessed using wrist-worn ActiGraph wGT3X-BT accelerometer, worn continuously (24 h/day) for seven consecutive days. Participants were required to provide at least three valid weekdays and one valid weekend day, with ≥20 hours of wear time per day. Sedentary behavior and physical activity intensity were classified using cut-points developed for wrist-worn ActiGraph accelerometers in free-living adults.
RESULTS:
A total of 265 participants (51% female) provided valid accelerometer measurements and were included in the analysis. Participants slept an average of 7.24 hours per day (SD = 2.29). Mean sedentary time was 10.57 hours per day (SD = 0.51). Average light PA (LPA) was 3.45 hours per day (SD = 1.44), while moderate-to-vigorous physical activity (MVPA) averaged 2.01 hours per day (SD = 1.36).
CONCLUSION:
The findings indicate that 36-year-old Icelanders spend a large proportion of their waking hours in sedentary behavior. Low variability in sedentary time suggests that most individuals remain inactive throughout the day. In contrast, MVPA and sleep showed high variability, reflecting substantial inter-individual differences in activity and sleep patterns. Representing roughly 5% of the Icelandic population born in 1988, this nationally representative cohort provides valuable, objective insights into movement behaviors in early adulthood. Given that excessive sedentary time is associated with poorer health outcomes, replacing sedentary behavior with physical activity of any intensity is recommended to reduce health risks and promote overall well-being.