Multilevel allometric modelling of maximum cardiac output, maximum arteriovenous oxygen difference, and peak oxygen uptake in 11–13-year-olds

Purposes To investigate longitudinally (1) the contribution of morphological covariates to explaining the development of maximum cardiac output ( Q̇ Q˙ max) and maximum arteriovenous oxygen difference (a-vO 2 diff max), (2) sex differences in Q̇ Q˙ max and a-vO 2 diff max once age, maturity status, and morphological covariates have been controlled for, and, (3) the contribution of concurrent changes in morphological and cardiovascular covariates to explaining the sex-specific development of peak oxygen uptake ( VO₂ V˙O2 ). Methods Fifty-one (32 boys) 11–13-year-olds had their peak VO₂ V˙O2 , maximum heart rate (HR max), Q̇ Q˙ max, and a-vO 2 diff max determined during treadmill running on three annual occasions. The data were analysed using multilevel allometric modelling. Results There were no sex differences in HR max which was not significantly ( p > 0.05) correlated with age, morphological variables, or peak VO₂ V˙O2 . The best-fit models for Q̇ Q˙ max and a-vO 2 diff max were with fat-free mass (FFM) as covariate with age, maturity status, and haemoglobin concentration not significant ( p > 0.05). FFM was the dominant influence on the development of peak VO₂ V˙O2 . With FFM controlled for, the introduction of either Q̇ Q˙ max or a-vO 2 diff max to multilevel models of peak VO₂ V˙O2 resulted in significant ( p < 0.05) additional contributions to explaining the sex difference. Conclusions (1) With FFM controlled for, there were no sex differences in Q̇ Q˙ max or a-vO 2 diff max, (2) FFM was the dominant influence on the development of peak VO₂ V˙O2 , and (3) with FFM and either Q̇ Q˙ max or a-vO 2 diff max controlled for, there remained an unresolved sex difference of ~ 4% in peak VO₂ . V˙O2.