LAUSR

BACKGROUND The study aimed to examine predicted differences of 2 different behavior change patterns on physical fitness (PF). METHODS Participants were 241 students (51% girls) aged 11-14 years from China. Light physical activity, moderate to vigorous physical activity (MVPA), and sedentary behavior (SB) were objectively measured. Sleep was obtained by subtracting from awake time. According to Chinese National student PF standards, 5 components of PF, including body mass index, cardiorespiratory fitness, speed, muscular explosive power and strength endurance, and flexibility, were assessed. The effects of different time reallocations between 24-hour movement behaviors on PF were estimated based on adjusted compositional multiple linear regression models with isometric log ratios. RESULTS Compared with MVPA substituting for the remaining behaviors, MVPA replacing SB or light physical activity produced more favorable changes on the comprehensive PF score, cardiorespiratory fitness, explosive power, and speed. MVPA replacing 30 minutes of SB was associated with favorable changes in PF (+1.9 [0.53, 3.18] points), 50-m run (-0.17 [-0.31, -0.04] s), long-distance running (-5.54 s [for girls]/7.25 s [for boys]), and long jump (+0.05 [0.01, 0.09] m). When sleep replaced SB, PF improved. CONCLUSIONS MVPA substituting SB or light physical activity is a strategy with a greater improvement in PF.