Individual variations in pre-altitude hemoglobin mass influence hemoglobin mass responses to repeated altitude sojourns.

Introduction: Previous studies have shown variable within-subject hemoglobin mass (Hb _mass ) responses to altitude training. We investigated whether Hb _mass responses depend on individual variations in pre-altitude Hb _mass during repeated altitude sojourns.
Methods: Nine elite endurance athletes carried out 3-5 altitude sojourns over 17 ± 10 months (mean ± 95% confidence interval), at an altitude of 1976 ± 62 m, for 21 ± 1 days, and a total hypoxic dose of 989 ± 46 km·h, with Hb _mass assessed before and after each sojourn (carbon monoxide rebreathing). The individual mean baseline was calculated as the mean of all pre-altitude Hb _mass values for an athlete, and it was investigated whether the percent deviation from the individual mean baseline affected the altitude-induced Hb _mass response.
Results: On average, Hb _mass increased by 3.4 ± 1.1% (p < 0.001) from pre- to post-altitude. The intra-individual changes in Hb _mass were highly inconsistent (coefficient of variation, CV: 88%), and we found no relationship between Hb _mass changes in successive altitude sojourns (r = 0.01; p = 0.735). However, the percent increase in Hb _mass was highly correlated with the pre-altitude Hb _mass , expressed as the percent deviation from the individual mean baseline (y = -0.7x + 3.4; r = 0.75; p < 0.001). Linear mixed-model analysis confirmed a -0.6 ± 0.2% smaller increase in Hb _mass for each 1% higher pre-altitude Hb _mass than the individual mean baseline (p < 0.001) after adjusting for the covariates hypoxic dose (p = 0.032) and the relative Hb _mass (g·kg ^-1 body weight; p = 0.031).
Conclusion: Individual variations in pre-altitude Hb _mass significantly influence the athletes' Hb _mass responses to repeated altitude sojourns, with a potentiated response after traveling to altitude with a low pre-altitude Hb _mass .
(© 2022 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)