Individual hemoglobin mass response to normobaric and hypobaric "live high-train low": A one-year crossover study

Purpose: To compare individual hemoglobin mass (Hb_mass) changes following a live high-train low (LHTL) altitude training camp under either normobaric hypoxia (NH) or hypobaric hypoxia (HH) conditions in endurance athletes. Methods: In a crossover design with a one-year washout, 15 male triathletes randomly performed two 18-d LHTL training camps in either HH or NH. All athletes slept at 2250 m and trained at altitudes < 1200 m. Hb_mass was measured in duplicate with the optimized carbon monoxide rebreathing method before (pre-) and immediately after (post-) each 18 d training camp. Results: Hb_mass increased similarly in HH (916 to 957 g, 4.5 ± 2.2%, P < 0.001) and in NH (918 to 953 g, 3.8 ± 2.6%, P < 0.001). Hb_mass changes did not differ between HH and NH (P = 0.42). There was substantial inter-individual variability among subjects to both interventions (i.e., individual responsiveness, or the individual variation in the response to an intervention free of technical noise): 0.9% in HH and 1.7% in NH. However, a correlation between intra-individual delta Hb_mass changes (%) in HH and in NH (r = 0.52, P = 0.048) was observed. Conclusion: HH and NH evoked similar mean Hb_mass increases following LHTL. Among the mean Hb_mass changes, there was a notable variation in individual Hb_mass response, which tended to be reproducible.

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