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

Introduction: To a considerable extent, the magnitude of blood volume (BV) and hemoglobin mass (Hbmass) contribute to the maximum O-2-uptake (VO(2)max), especially in endurance-trained athletes. However, the development of Hbmass and BV and their relationships with VO(2)max during childhood are unknown. The aim of the present cross-sectional study was to investigate Hbmass and BV and their relationships with VO(2)max in children and adolescents. In addition, the possible influence of endurance training and chronic hypoxia was evaluated.Methods: A total of 475 differently trained children and adolescents (girls n = 217, boys n = 258; untrained n = 171, endurance trained n = 304) living at two different altitudes (similar to 1,000 m, n = 204, similar to 2,600 m, n = 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(2)max was determined by cycle ergometry and for runners on the treadmill.Results: 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 similar to 7% on Hbmass in all groups and no effect on BV. The VO(2)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.Conclusions: The associated effects of training on Hbmass and BV, resulting in increased VO(2)max, can only be observed after the onset of puberty.