24-H movement behaviors and physical fitness in preschoolers: A compositional and isotemporal reallocation analysis.

Background/objectives: This study examined the relationships between 24-h movement behaviors and physical fitness (PF) in preschool children.

Methods: The study was conducted on 474 children aged 3-6 years in Zhuhai. Physical activity (PA) and sedentary behavior (SB) were collected by the accelerometer, and sleep time was assessed through the parent-report questionnaire. Balance, cardiorespiratory fitness (CRF), flexibility, muscle strength, muscular endurance, and speed-agility were measured using a balance beam test, 20 m shuttle run test, sit and reach test, handgrip test, sit-ups, and 4 × 10 m shuttle run test respectively. The compositional data analysis was used to examine the association between 24-h movement behaviors and PF, and the compositional isotemporal substitution analysis was used for the time reallocation.

Results: The daily composition, adjusted for age, gender, and body mass index (BMI), was significantly associated with CRF (p < 0.001, r = 0.20), flexibility (p < 0.001, r = 0.07), muscular strength (p < 0.001, r = 0.37), muscular endurance (p < 0.001, r = 0.26), and speed-agility (p < 0.001, r = 0.26). The addition of moderate-to-vigorous PA (MVPA) at the expense of SB and sleep, MVPA at the cost of sleep, was associated with significant muscular strength and speed-agility improvements respectively. The impact of SB and sleep replacing MVPA is stronger than MVPA replacing SB and sleep on muscular strength.

Conclusion: These findings offer useful insight for the replacement of movement behaviors within the recommended range to facilitate PF development in early childhood.