The impact of school life and holidays on sleep and physical activity patterns in junior high school students: a small-sample longitudinal study using wearable devices.

Background: The structured day hypothesis posits that the characteristics of a structured school environment play a protective role in adolescents' physical activity. Existing studies predominantly rely on subjective reports or short-term monitoring, lacking longitudinal objective evidence that covers a full academic year cycle for Chinese students who are under high academic pressure. Objective: This study employs long-term objective monitoring through wearable devices to systematically compare sleep and physical activity patterns among Chinese middle school students across four phases: study days, weekend days, winter vacation, and summer vacation, while also analyzing gender differences. Methods: A longitudinal study was conducted involving 27 first-year middle school students (14 boys and 13 girls) from a middle school in Nanjing. The Huawei Band 6 was utilized to continuously monitor sleep parameters, including sleep onset time, wake-up time, duration of deep, light, and REM sleep, as well as total sleep duration. Additionally, physical activity parameters such as step count, MVPA, and continuous MVPA were recorded during the specified four stages. A linear mixed-effects model was employed to analyze the effects of both stage and gender. Results: On school days, insufficient sleep was observed alongside relatively high levels of physical activity, with only 26.71% of participants meeting the sleep adequacy standard and 34.30% achieving the MVPA target. During holidays, sleep quality improved while physical activity levels decreased, with the MVPA compliance rate among girls dropping to a mere 3.83% on weekend days. In contrast, winter vacation showed significantly higher total sleep duration, deep sleep duration, and step counts compared to summer vacation. Notably, girls exhibited longer deep sleep duration than boys; however, their step counts and MVPA levels were significantly lower than those of boys. Conclusion: Structured school schedules promote the maintenance of physical activity; however, they may also lead to increased sleep deprivation. In contrast, holidays tend to improve sleep quality but are linked to a significant decline in physical activity levels. Therefore, it is imperative to optimize daily routines during school days to ensure adequate sleep. Furthermore, establishing a collaborative intervention mechanism that involves families, schools, and communities during holidays can encourage physical activity and reduce sedentary behavior and screen time, particularly among female students and during summer vacations.