To investigate the association between 24-hour activity behavior and body composition among primary and secondary school students using compositional data analysis method, so as to provide scientific guidance for optimizing daily activity allocation and improving physical health.

In June 2021, following the principle of random cluster sampling, 349 primary and middle school students were selected by lottery method from Taiyuan City, Shanxi Province. Compositional multiple regression analysis was conducted to examine the relationship between different 24-hour activity behaviors and body composition indicators. The isotemporal substitution model was adopted to examine the quantitative effects of substituting 10 or 20 minutes among activity behaviors on body composition.

In girls, sedentary behavior (SB) time was negatively correlated with fat-free mass (FFM) (β=-4.81); in boys, moderate-to-vigorous physical activity (MVPA) time was positively correlated with FFM (β=7.01), while light physical activity (LPA) time was negatively correlated with FFM (β=-9.26) and positively correlated with body fat percentage (FAT%) (β=0.09) (all P < 0.01). Isocaloric substitution analysis revealed that replacing the same duration of MVPA with SB, sleep (SL), or LPA for 10 or 20 minutes produced significantly greater adverse effects compared to the beneficial effects of MVPA substitution. Replacing MVPA with LPA for 10 minutes resulted in 1.01% increase in FAT% and 0.91% decrease in reverse substitution for boys; replacing MVPA with SB or SL for 10 minutes resulted in a decrease of 1.10 kg and 1.16 kg in FFM for boys, 0.81 kg and 0.74 kg for girls, and reverse substitution increased by 0.92 and 0.97 kg, 0.65 and 0.58 kg, respectively (all P < 0.05). When LPA, SB or SL were replaced with MVPA for 20 minutes, the trend of change were basically consistent (all P < 0.05).

Activity behaviors of 24-hour are associated with body composition among primary and secondary school students. MVPA is the primary influential component.