Structured-unstructured activity behaviours on preschoolers' mental and physical health: a compositional and isotemporal reallocation analysis

This study analysed the relationship between the structured and unstructured activities of preschoolers and their mental and physical health, and also investigated the predicted changes in mental and physical health by reallocating activity time. This cross-sectional study was carried out with 324 preschoolers. Video recording and SOPARC activity observation system was used for the division of structured and unstructured activities. An accelerometer sensor was used to measure activity intensity. The SDQ psychological questionnaire was adopted to collect data on internalizing difficulties, externalizing difficulties, total difficulties and pro-social behaviours. Physical indices including body shape (height, weight, BMI), and physical fitness (upper and lower limb strength, flexibility, agility, and balance) were collected using Chinese toddler physical fitness measurement tools. Component data and isotemporal reallocation analyses were conducted using R Studio (Version 4.2). A total of 308 preschoolers (160 boys; aged 4.50 +/- 0.93 years) were included in the data analysis. The activities composition, adjusted for sex, area, mental level (for mental indicators), or age (for physical indicators), was significantly correlated with various measurement indicators (p < 0.05). Specifically, structured (beta=-0.87, p < 0.05) and unstructured (beta=-1.24, p < 0.05) moderate-to-vigorous physical activity (MVPA) were significantly positive correlated with internalizing difficulties, while structured MVPA was significantly positively correlated with body shape (beta = 2.17, p < 0.05). Replacing structured light physical activity (LPA) with 10 min of structured MVPA has a positive effect on internalizing difficulties (SMD=-1.28, 95%CI: -2.30 to -0.27) and body shape (SMD = 1.76, 95%CI: 0.37 to 3.15). When the total replacement time reaches 25 min, the benefits become even more pronounced. Structured and unstructured MVPA are both beneficial to preschoolers' mental and physical health, with the incorporation of MVPA for over 25 min in structured activities and supplementary unstructured MVPA yielding even greater benefits.