Accumulated Effects of 24 Hours Physical Activity,Sedentary Behavior,and Sleep on Cardiorespiratory Fitness in College Students.

Objective To explore the accumulated effects of physical activity,sedentary behavior,and sleep on cardiorespiratory fitness(CRF)among college students and provide effective measures for enhancing their CRF. Methods From May to June in 2023,223 college students aged 18 to 24 years old were recruited from Tianjin University of Science and Technology for a 24 hours activity behavior survey and CRF testing.Compositional analysis was employed to investigate the relationships of physical activity,sedentary behavior,and sleep with CRF.Isotemporal substitution models were established to predict the effects of substituting various activity behaviors on CRF.Results The proportion of time spent on moderate-to-vigorous physical activity(MVPA)was positively correlated with CRF of college students(β=6.40,P=0.002),while the proportion of time spent on sedentary behavior was negatively correlated with CRF(β=-3.02,P=0.004).Light physical activity(LPA)and sleep were not correlated with CRF(β=-1.06,P=0.504).Isotemporal substitution results for 15-min increments showed that replacing other activity behaviors with MVPA significantly increased the CRF of college students[SB:1.72 mL/(kg·min),95% CI=0.94-2.51;LPA:1.82 mL/(kg·min),95% CI=0.95-2.68;sleep:1.64 mL/(kg·min),95% CI=0.84-2.45].In the dose-response relationship from -30 min to 30 min,reallocating time from other behaviors to MVPA had greater adverse effect on CRF than reallocating time from MVPA to other behaviors.Among all the substitutions,replacing LPA with MVPA had the most beneficial effect on improving CRF.Additionally,a 5-min increment was considered the optimal tipping point for MVPA replacing other activities.Conclusions This study underscores the importance of participating in MVPA for improving the CRF of college students.The isotemporal substitution model provides clear goals for the allocation of time for these behaviors,aiding in future intervention measure development and policy-making.