Association between cardiorespiratory fitness level and insulin resistance in adolescents with various obesity categories

BACKGROUND An association between cardiorespiratory fitness(CRF)and insulin resistance in obese adolescents,especially in those with various obesity categories,has not been systematically studied.There is a lack of knowledge about the effects of CRF on insulin resistance in severely obese adolescents,despite their continuous rise.AIM To investigate the association between CRF and insulin resistance in obese adolescents,with special emphasis on severely obese adolescents.METHODS We performed a prospective,cross-sectional study that included 200 pubertal adolescents,10 years to 18 years of age,who were referred to a tertiary care center due to obesity.According to body mass index(BMI),adolescents were classified as mildly obese(BMI 100% to 120% of the 95^(th)percentile for age and sex)or severely obese(BMI≥120% of the 95^(th)percentile for age and sex or≥35 kg/m^(2),whichever was lower).Participant body composition was assessed by bioelectrical impedance analysis.A homeostatic model assessment of insulin resistance(HOMA-IR)was calculated.Maximal oxygen uptake(VO_(2)max)was determined from submaximal treadmill exercise test.CRF was expressed as VO_(2)max scaled by total body weight(TBW)(mL/min/kg TBW)or by fat free mass(FFM)(mL/min/kg FFM),and then categorized as poor,intermediate,or good,according to VO_(2)max terciles.Data were analyzed by statistical software package SPSS(IBM SPSS Statistics for Windows,Version 24.0).P<0.05 was considered statistically significant.RESULTS A weak negative correlation between CRF and HOMA-IR was found[Spearman’s rank correlation coefficient(rs)=-0.28,P<0.01 for CRF_(TBW);(r_(s))=-0.21,P<0.01 for CRF_(FFM)].One-way analysis of variance(ANOVA)revealed a significant main effect of CRF on HOMA-IR[F(2200)=6.840,P=0.001 for CRF_(TBW);F_((2200))=3.883,P=0.022 for CRF_(FFM)].Subsequent analyses showed that obese adolescents with poor CRF had higher HOMA-IR than obese adolescents with good CRF(P=0.001 for CRF_(TBW);P=0.018 for CRF_(FFM)).Two-way ANOVA with Bonferroni correction confirmed significant effect of interaction of CRF level and obesity category on HOMA-IR[F_((2200))=3.292,P=0.039 for CRF_(TBW)].Severely obese adolescents had higher HOMA-IR than those who were mildly obese,with either good or poor CRF.However,HOMA-IR did not differ between severely obese adolescents with good and mildly obese adolescents with poor CRF.CONCLUSION CRF is an important determinant of insulin resistance in obese adolescents,regardless of obesity category.Therefore,CRF assessment should be a part of diagnostic procedure,and its improvement should be a therapeutic goal.

Body Composition Estimatives by Anthropometry, Bioelectrical Impedance and Deuterium Oxide Dilution in Obese Adolescents

To evaluate the relationship between measures of body composition in obese adolescents by the methods of bioelectrical impedance analysis, deuterium oxide dilution and anthropometric measures, proposing an equation. The variables were weight, height, BMI, triceps and subscapular skinfold thickness, waist and arm muscle circumference, lean body mass, fat mass and total body water by bioelectrical impedance and deuterium oxide dilution methods. The study included 40 obese adolescents, 45% male, age distribution was 2.42 ± 1.19 years and females 55%, and the predominant age was 12.61 ± 1.78. Linear regression equations were developed, capable of predicting body composition from information supplied by the method of deuterium oxide dilution (gold standard), bioelectrical impedance and anthropometry. The variables gender, age, height, arm circumference, triceps and suprailiac skin fold thickness, resistance and reactance were used to estimate lean body mass, fat mass and total body water by the method of deuterium and significantly correlated with variables, resistance, reactance, sex and total body water (TBW) by bioimpedance method. Among the equations developed, five were suitable for this sample, therefore, it is suggested that more studies should be done to test the applicability of the equations in other samples so that we can validate the equations encountered in obese adolescents.

Determinants of moderate to vigorous physical activity and obesity in children:a structural equation modeling analysis

Background:The determinants of physical activity(PA)and body fatness in Chinese adolescents are rarely examined.This study aimed to investigate the effect of attitude toward PA,screen time,parents'socioeconomic status(SES),and exercise habit on PA and body fatness among Chinese children by using structural equation modeling(SEM)analysis.Methods:Data obtained from the second Community Fitness Survey in Hong Kong region were utilized,in which students from one secondary school of each of the 18 districts of Hong Kong were recruited.A total of 2517 questionnaires with physical fitness items were successfully distributed to students aged 13-19 years in these districts.Families'SES,parents'exercise habit,children's intention to participate in PA,amount of moderate to vigorous PA(MVPA),screen time,children's attitude toward PA,and children's body fat percentage were measured and analyzed with SEM.The structural equation model was composed of a measurement model and a structural model.The model was tested with Mplus 6.The Chi-square test,root mean square error of approximation,comparative fi t index,and Tucker-Lewis index were calculated to evaluate model fit.The model was then modifi ed based on the model fi t indices.Results:Children's intention to participate in PA was a strong predictor of their engagement in MVPA.Parents'exercise habit had both direct and indirect(via attitude)effects on their children's intention to participate in PA.Screen time was not a predictor of body composition.Children's intention to participate in PA directly affected their body composition.Children's attitude toward PA,parents'exercise habit,and SES had signifi cant effects on the children's intention to participate in PA.Furthermore,obesity had a negative effect on the children's attitude toward PA.Conclusions:To promote MVPA and prevent obesity in Chinese children of Hong Kong region,it is important to design intervention that enhances children's intention and attitude in PA,as well as parent's exercise habits.Tailormade programs that take SES into consideration are also essential.Further studies are necessary to extend the results and test the model in other metropolitan areas in China.