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 (Hbmass) responses to altitude training. We investigated whether Hbmass responses depend on individual variations in pre‐altitude Hbmass 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 Hbmass assessed before and after each sojourn (carbon monoxide rebreathing). The individual mean baseline was calculated as the mean of all pre‐altitude Hbmass values for an athlete, and it was investigated whether the percent deviation from the individual mean baseline affected the altitude‐induced Hbmass response. Results On average, Hbmass increased by 3.4 ± 1.1% (p