AUTHOR=Mancera-Soto Erica Mabel , Ramos-Caballero Diana Marcela , Rojas J. Joel A. , Duque Lohover , Chaves-Gomez Sandra , Cristancho-Mejía Edgar , Schmidt Walter Franz-Joachim 

TITLE=Hemoglobin Mass, Blood Volume and VO2max of Trained and Untrained Children and Adolescents Living at Different Altitudes

JOURNAL=Frontiers in Physiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2022.892247

DOI=10.3389/fphys.2022.892247

ISSN=1664-042X

ABSTRACT=<p><bold>Introduction:</bold> To a considerable extent, the magnitude of blood volume (BV) and hemoglobin mass (Hbmass) contribute to the maximum O<sub>2</sub>-uptake (VO<sub>2</sub>max), especially in endurance-trained athletes. However, the development of Hbmass and BV and their relationships with VO<sub>2</sub>max during childhood are unknown. The aim of the present cross-sectional study was to investigate Hbmass and BV and their relationships with VO<sub>2</sub>max in children and adolescents. In addition, the possible influence of endurance training and chronic hypoxia was evaluated.</p><p><bold>Methods:</bold> A total of 475 differently trained children and adolescents (girls <italic>n</italic> = 217, boys <italic>n</italic> = 258; untrained <italic>n</italic> = 171, endurance trained <italic>n</italic> = 304) living at two different altitudes (∼1,000 m, <italic>n</italic> = 204, ∼2,600 m, <italic>n</italic> = 271) and 9–18 years old participated in the study. The stage of puberty was determined according to Tanner; Hbmass and BV were determined by CO rebreathing; and VO<sub>2</sub>max was determined by cycle ergometry and for runners on the treadmill.</p><p><bold>Results:</bold> Before puberty, there was no association between training status and Hbmass or BV. During and after puberty, we found 7–10% higher values in the trained groups. Living at a moderate altitude had a uniformly positive effect of ∼7% on Hbmass in all groups and no effect on BV. The VO<sub>2</sub>max before, during and after puberty was strongly associated with training (pre/early puberty: boys +27%, girls +26%; mid puberty: +42% and +45%; late puberty: +43% and +47%) but not with altitude. The associated effects of training in the pre/early pubertal groups were independent of Hbmass and BV, while in the mid- and late pubertal groups, 25% of the training effect could be attributed to the elevated Hbmass.</p><p><bold>Conclusions:</bold> The associated effects of training on Hbmass and BV, resulting in increased VO<sub>2</sub>max, can only be observed after the onset of puberty.</p>