Determinants of Cardiorespiratory Fitness in a Population Sample of Girls and Boys Aged 6 to 8 Years

Background: There are few studies on determinants of cardiorespiratory fitness (CRF) among girls and boys separately in population samples of children. Methods: We therefore investigated the determinants of CRF, assessed by maximal workload per height using allometric scaling, in a population sample of 162 girls and 177 boys aged 6 to 8 years. We used automated bootstrap feature selection and linear regression models. Results: The strongest determinants of CRF among girls were maximal heart rate (HR; standardized regression coefficient [beta] = 0.31, P <.001), unsupervised physical activity = 0.29, P <.001), lean body mass (beta = 0.23, P =.001), and errors in static balance test (beta= -0.16, P =.02), accounting altogether for 25.7% of variation in CRF. In boys, unsupervised physical activity beta = 0.24, P <.001), resting HR (beta = 0.25, P <.001), hand grip strength (beta = 0.21, P =.001), errors in static balance test (beta = -0.16, P =.01), organized football (beta = 0.16, P =.01), and unsupervised trampoline jumping (beta = 0.14, P =.04) were the strongest determinants of CRF, accounting altogether for 29.7% of variation in CRF. Conclusions: These findings suggest that unsupervised physical activity is sufficient in improving CRF in both sexes. Furthermore, larger muscle mass and better balance are associated with higher CRF that has to,be taken into account when assessing CRF using maximal cycle ergometer exercise test among children.