An Empirical Study of Two 24-Hour Movement Substitution Models Based on Children’s Physical Fitness

Objective: To compare the effects of 24-hour movement substitution on physical fitness based on “one-to-one” isotemporal substitution and “one-to-three” proportional substitution. Methods: 302 children of grade 1-5 in Jinhua participated in this study, accelerometers were used to measure 24-hour movement including moderate-to-vigorous physical activity(MVPA), lightintensity physical activity(LPA), sedentary behavior(SED) and sleep(SLP) The physical fitness levels were measured according to the National Student Physical Health Standards(Revised in 2014). Compositional data analysis was used to explore the relationship between 24-hour movement time proportion and physical fitness. Results: 1) The results of two substitution models showed that the time substitution of MVPA with LPA, SED and SLP had a significant effect on children's physical fitness, while the substitution effect of LPA was not significant. 2) Significant differences were observed between the two substitution modes, the “one-to-one” isotemporal substitution results showed that MVPA had the strongest substitution effect, and the substitution of SED or SLP with other movements except MVPA for 10 minutes had no significant effect on physical fitness. The “dose-response” analysis results showed that the “point-to-point” substitution of MVPA with LPA, SED or SLP was asymmetrical. The “one-to-three” proportional substitution results showed that 10% substitution of SED or SLP with other three behaviors changed the physical fitness score significantly, and SED had the strongest substitution effect. In addition, the substitution of 24-hour movement behaviors was symmetrical. Conclusions: The “one-to-three” proportional substitution model can provide more reliable research evidence for the relationship between time usage and health outcomes, and it is more in line with real-life activity scenarios.