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

Abstract

Purposes: To investigate longitudinally (1) the contribution of morphological covariates to explaining the development of maximum cardiac output (Q ˙ max) and maximum arteriovenous oxygen difference (a-vO2 diff max), (2) sex differences in Q ˙ max and a-vO2 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 (V˙ O 2). Methods: Fifty-one (32 boys) 11–13-year-olds had their peak V˙ O 2, maximum heart rate (HR max), Q ˙ max, and a-vO2 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 V˙ O 2. The best-fit models for Q ˙ max and a-vO2 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 V˙ O 2. With FFM controlled for, the introduction of either Q ˙ max or a-vO2 diff max to multilevel models of peak V˙ O 2 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 Q ˙ max or a-vO2 diff max, (2) FFM was the dominant influence on the development of peak V˙ O 2, and (3) with FFM and either Q ˙ max or a-vO2 diff max controlled for, there remained an unresolved sex difference of ~ 4% in peak V˙ O 2.