Objective To study the association between 24-hour movement behaviors (24 h MB) and fundamental movement skills (FMS) in preschool children using compositional data analysis, and the expected changes in preschool children's FMS after isochronous substitution between movement behaviors.

Methods The ActiGraph wGT3-BT accelerometer was used to measure the data of physical activity (PA) and sedentary behavior (SB) of 323 children aged 3-6 years (181 boys and 142 girls); FMS was measured by Test of Gross Motor Development (TGMD-3), and sleep time was reported by parents. The descriptive statistical analysis, multivariate linear model and isochronous substitution of compositional data were all completed by R software.

Results ① The time distribution of preschool children's 24 h MB was closely related to their motor development. The time spent on MVPA was the most stable, and the probability of conversion to light physical activity (LPA) time was the highest; ② Preschool children's MVPA had the greatest influence on locomotor and total motor skill (Total MS), MVPA isochronous substitution for other behaviors had positive benefits, among which the effect of replacing LPA was the most obvious. Replacing MVPA in other behaviors indicated lower motor skill, and the prediction was asymmetrical.

Conclusion Although MVPA had the greatest influence on preschool children's motor skill development, it is needed to consider the impact of 24 h MB on motor skill development from an overall perspective. In early education, it is important for kindergarten, families and communities to reallocate preschool children's LPA to MVPA in order to obtain better development of FMS.