Ethics approval. This study was performed in line with the ethical guidelines of the Declaration of Helsinki 1964 (last revision of Fortaleza, Brazil, 2013 and approved by the Research Ethics Committee of the University Jaume I of Castellon (Spain).Consent to participate. Adolescents and their parents or guardians were informed of the nature and characteristics of the study, and all provided a written informed consent. Consent for publication. No applicable.Availability of the data and material. No applicable.Code availability. No applicable.

Purpose. The purpose of the present study is to investigate the individual and combined impact of physical fitness components at baseline on health-related quality of life (HRQoL) at 24-month follow-up in adolescents.Methods. This longitudinal research included 199 adolescents (13.9 ± 0.3 years at baseline) from DADOS study. Cardiorespiratory fitness was assessed using the 20m shuttle run test. Muscular strength was assessed using the standing broad jump test. Motor competence was assessed using the 4×10m shuttle run test. A physical fitness z-score was calculated as the mean of the z-scores values of each fitness test. A fitness index ranging from 0 to 3 was created according to the number of physical fitness components in which participants achieved high levels according to normative values. HRQoL was evaluated by the KIDSCREEN-10 questionnaire.Results. Linear regression analyses showed that cardiorespiratory fitness, muscular strength, and the physical fitness z-score at baseline were individually associated with HRQoL at follow-up (β ranging from 0.123 to 0.183; all p<0.05). Moreover, logistic regression analysis revealed that adolescents with a fitness index ≥1 at baseline were more likely to achieve high HRQoL at 24month follow-up, compared with their peers with an index of 0 (OR ranging from 3.554 to 9.087; all p<0.05).Conclusions. Our results revealed an individual and cumulative positive impact of physical fitness at baseline on HRQoL at 24-month follow-up. These findings underline the key role of promoting the enhancement of overall physical fitness components in order to improve adolescents' health and well-being.

Aims: The aims were (1) to analyse the cross-sectional and longitudinal associations between children’s cardiorespiratory fitness (CRF) and health-related quality of life (HRQoL) and (2) to examine whether these associations were mediated by physical activity self-efficacy and physical activity enjoyment. Methods: This study involved 383 children (10.0 ± 0.5 years) recruited from 20 primary schools in northwest England. Data were collected on two occasions 12 weeks apart. The number of laps completed in the 20-m Shuttle Run Test was used as the CRF indicator. HRQoL was assessed using the KIDSCREEN-10 questionnaire. Physical activity self-efficacy and enjoyment were assessed with the social-cognitive and Physical Activity Enjoyment Scale questionnaires, respectively. Linear mixed models with random intercepts (schools) assessed associations between CRF and HRQoL cross-sectionally, and longitudinally. Boot-strapped mediation procedures were performed, and indirect effects (IE) with 95% confidence intervals (CI) not including zero considered as statistically significant. Analyses were adjusted for sex, time of the year, socioeconomic status, waist-to-height ratio, maturation, and physical activity. Results: CRF was cross-sectionally associated with HRQoL (β = 0.09, 95% CI = 0.02, 0.16; p = .015). In the longitudinal analysis, CRF at baseline was associated with HRQoL at 12 weeks after additionally controlling for baseline HRQoL (β = 0.08, 95% CI = 0.002; p = .15, p = .045). Cross-sectionally, physical activity self-efficacy and enjoyment acted individually as mediators in the relationship between CRF and HRQoL (IE = 0.069, 95% CI = 0.038; p = .105 and IE = 0.045, 95% CI = 0.016; p = .080, respectively). In the longitudinal analysis, physical activity self-efficacy showed a significant mediating effect (IE = 0.025, 95% CI = 0.004; p = .054). Conclusion: Our findings highlight the influence of CRF on children’s psychological correlates of physical activity and their overall HRQoL.