A Study Of Dose-Response Relationship Between Physical Activity And Health-Related And Metabolic-Related Physical Fitness Improvement In Obese Children And Adolescents

Objective: To explore the dose-response relationship between physical activity and improvements in physical fitness among obese children and adolescents,and to analyze whether there is a threshold of physical activity that achieves optimal improvement effects.Methods: 102 participants were randomly recruited from a closed weight loss training camp.All participants received 4 weeks of exercise training during the camp and their physical activity was monitored using Acti Graph GT3X+ triaxial accelerometers.Health-related physical fitness and metabolic-related physical fitness indicators were collected before and after the intervention.Improvement in physical fitness indicators was represented by the "Δ+ indicator," which was calculated as the difference between the indicator value after and before the intervention.Paired sample t-tests were used to analyze changes in indicators before and after the 4-week training.Dose-response relationships between physical activity and improvements in physical fitness indicators and threshold effects were analyzed using simple linear regression,segmented linear regression,and restricted cubic splines(RCS).Likelihood ratio tests were used to analyze the differences between linear regression and segmented regression.Results:(1)After 4 weeks of physical activity training intervention,the body composition,cardiorespiratory fitness,grip strength,glucose and lipid metabolism indicators of obese children and adolescents improved significantly compared with before intervention(P<0.05).(2)For every increase of 1 min/day in moderate-tovigorous intensity physical(MVPA),the degree of decrease in body fat and body fat percentage increased by 0.015 kg(β=-0.015,P<0.05)and 0.016%(β=-0.016,P<0.05),respectively.(3)There was a significant non-linear relationship between daily step count and improvement in body fat mass,body fat percentage,lean body weight,and skeletal muscle mass(P-Nonlinear<0.05).When the step count was ≤11200 steps/day,for every increase of 1000 steps/day,the degree of decrease in body fat and body fat percentage increased by 0.731 kg(β=-0.731,P<0.05)and 0.944 kg(β=-0.944,P<0.05),respectively.However,when the step count was >11200 steps/day,the improvement in body fat mass and body fat percentage decreased with an increase in step count(βvalues were 0.411 and 0.606,respectively,P<0.05).When the step count was ≤11400steps/day,for every increase of 1000 steps/day,the degree of increase in lean body mass and skeletal muscle mass increased by 0.637 kg(β=0.637,P<0.05)and 0.293 kg(β=0.293,P<0.05),respectively.However,when the step count was >11400 steps/day,further increase in daily step count would lead to accelerated loss of lean body mass and skeletal muscle mass(β values were-0.635 and-0.388,respectively,P<0.05).(4)There was a significant non-linear relationship between daily MVPA duration and improvement in maximal oxygen uptake and LDL-C(P-Nonlinear<0.05).When the MVPA was ≤98.9 min/day,for every increase of 1 min/day in MVPA,the degree of increase in maximal oxygen consumption increased by 0.110 ml/kg/min(β=0.110,P<0.05).However,when the MVPA was >98.9 min/day,further increase in MVPA duration did not lead to additional improvement in maximal oxygen consumption(β=-0.023,P>0.05).When the MVPA was ≤77.1 min/day,increasing MVPA duration did not lead to additional decrease in LDL-C(β=0.006,P<0.05).Only when the MVPA was >77.1 min/day,increasing MVPA duration could further decrease LDL-C level(β=-0.007,P<0.05).Conclusion:(1)Four weeks of physical activity training can significantly improve the partial health-related physical fitness and metabolic-related physical fitness of obese children and adolescents.(2)For obese children and adolescents,the dose-response curve between daily step counts and improvements in body fat mass,fat percentage,and systolic blood pressure follows a "U-shaped" curve,while the dose-response curve for improvements in skeletal muscle mass and lean body mass follows an "inverted Ushaped" curve.Daily step counts in the range of 11,200 to 11,400 steps can achieve the optimal effect of improving body composition and effectively reducing systolic blood pressure.(3)The daily duration of MVPA in the range of 77.1 to 98.9 minutes is a safe and effective way to improve LDL-C and maximal oxygen consumption in obese children and adolescents.