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.

Physical activity (PA) in preschool children (3-to 5-year olds) is characterized by short bouts of intermittent movement, generally accumulated during free play activities. Little is known about how the amount of PA or the patterns of PA accumulation are related to health in preschoolers. Ninety-six healthy preschool children (46 boys, 50 girls; 4.4 ± 0.9 years) participated in assessments of PA, body composition, health-related fitness, blood pressure, and motor proficiency. PA data were collected for 7 consecutive days using Actigraph accelerometers. PA prevalence was assessed by the amount of total and moderate-to-vigorous PA (MVPA) in min/day and as a % of wear; PA patterns were assessed by the frequency and duration of MVPA bouts and by the duration of breaks between MVPA. Younger preschoolers engaged in less PA than older preschoolers, according to measures of prevalence and patterns (p < 0.05). Girls participated in less PA, less frequent MVPA, and longer breaks between bouts of MVPA compared to boys (p ≤ 0.001, for all). Health-related fitness was higher in preschoolers who engaged in more total PA, more frequent bouts of MVPA, longer bouts of MVPA, and shorter breaks between bouts of MVPA (p < 0.05, for all). Blood pressure was higher in preschoolers taking longer breaks between bouts of MVPA (p < 0.05). Motor proficiency was poorer in preschoolers who participated in shorter bouts of MVPA (p < 0.001). Preschoolers who met current PA recommendations of 180 min of total PA and 60 min of MVPA daily had better body composition and health-related fitness, respectively, compared to their peers who did not meet recommendations (p < 0.05). To the best of our knowledge, these iv data are the first to provide support for new PA guidelines and to demonstrate relationships between PA and health-related fitness and blood pressure in preschoolers.Our findings indicate that PA patterns are just as important as PA prevalence in describing relationships between health measures in preschool children.v