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

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.

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.

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).

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 .