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Background In adolescence there are several biological and physiological changes associated with overweight and obesity. Objective The purpose of this study was to analyze the associations between health-related quality of life (HRQoL) and body mass index (BMI) in adolescents. Methods This is a cross-sectional analysis of 957 Portuguese adolescents (446 girls and 511 boys) aged 12-18 years. A series of variables were collected: (a) HRQoL was assessed using the KIDSCREEN-10 questionnaire; (b) socioeconomic status (SES) was measured using the Family Affluence Scale; (c) body composition (weigh, height) were measured and BMI was calculated and, (d) pubertal stage was assessed with Tanner stages; (e) the 20-m shuttle-run was used to estimate cardiorespiratory fitness. Regression models and mediation analysis were performed to assess the association between HRQoL and BMI. Results HRQoL was significantly higher in boys than girls (p < 0.05). The prevalence of overweight and obesity was 23.5% and 6.7% in girls, and 21.3% and 5% in boys, respectively. HRQoL was inversely and significantly associated with BMI in boys (B = -0.130; p < 0.05) and girls (B = -0.148; p < 0.05) after controlling for age, pubertal stage and SES. Cardiorespiratory fitness act as a full mediator variable on the relationship between BMI and HRQoL in adolescents (p < 0.05). Conclusion Our results suggest that cardiorespiratory fitness acted as a full mediator in the relationship between BMI and HRQoL, in adolescents. Public health policies targeting a wealthy weight and an improved physical fitness level could be a strategy of particular interest for improving the HRQoL of adolescents. [ABSTRACT FROM AUTHOR]

Adolescents' physical fitness levels are an important indicator of their lifestyle and seem to have positive consequences in health-related quality of life (HRQoL). The purpose of this study is to analyse the combined associations of cardiorespiratory fitness and muscular fitness with HRQoL and to assess the differences between HRQoL scores across groups of cardiorespiratory fitness and muscular fitness in Portuguese adolescents. This is a cross-sectional analysis with 567 Portuguese adolescents aged 12-18 years-old. HRQoL was measured using the Kidscreen-10 questionnaire. Cardiorespiratory fitness was estimated with the 20-m shuttle-run test. Muscular fitness was evaluated using the handgrip and the standing long jump tests and a muscular fitness index was computed by means of standardized measures of both tests. Socioeconomic status was assessed using the Family Affluence Scale. Body composition (body mass and height) was measured according to standard protocols. Accelerometers were used to obtain objective physical activity time. Pubertal stage was assessed using Tanner stages. Adherence to the Mediterranean diet was assessed using the KIDMED index. Participants were divided into four groups based on low or high values of both cardiorespiratory and muscular fitness. Regression analysis, mediation analysis and ANCOVA were performed. HRQoL was positively associated with cardiorespiratory fitness (B = 0.112; p < 0.05) and muscular fitness score (B = 0.328 p < 0.05), after controlling for potential confounders. However, when both fitness variables were entered in the same model only cardiorespiratory fitness remained significantly associated with HRQoL (B = 0.093 p < 0.05). Cardiorespiratory fitness acted as a full mediator variable on the relationship between muscular fitness and HRQoL in adolescents (p < 0.05). ANCOVA showed that adolescents with high cardiorespiratory fitness/high muscular fitness exhibit better HRQoL scores when compared to those with low muscular fitness/low cardiorespiratory fitness and with those with low muscular fitness/high cardiorespiratory fitness (p < 0.05). In adolescents, the combination of high cardiorespiratory fitness and high muscular fitness was positively associated with a better HRQoL. [ABSTRACT FROM AUTHOR]