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 ([Formula: see text] max) and maximum arteriovenous oxygen difference (a-vO(2) diff max), (2) sex differences in [Formula: see text] 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 ([Formula: see text] ). METHODS: Fifty-one (32 boys) 11–13-year-olds had their peak [Formula: see text] , maximum heart rate (HR max), [Formula: see text] 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 [Formula: see text] . The best-fit models for [Formula: see text] 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 [Formula: see text] . With FFM controlled for, the introduction of either [Formula: see text] max or a-vO(2) diff max to multilevel models of peak [Formula: see text] 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 [Formula: see text] max or a-vO(2) diff max, (2) FFM was the dominant influence on the development of peak [Formula: see text] , and (3) with FFM and either [Formula: see text] max or a-vO(2) diff max controlled for, there remained an unresolved sex difference of ~ 4% in peak [Formula: see text]