Time course of the hemoglobin mass response to natural altitude training in elite endurance cyclists

To determine the time course of hemoglobin mass (Hb_mass) to natural altitude training, Hb_mass, erythropoietin [EPO], reticulocytes, ferritin and soluble transferrin receptor (sTfR) were measured in 13 elite cyclists during, and 10 days after, 3 weeks of sea level (n=5) or altitude (n=8, 2760 m) training. Mean Hb_mass, with a typical error of ～2%, increased during the first 11 days at altitude (mean ± standard deviation 2.9 ± 2.0%) and was 3.5 ± 2.5% higher than baseline after 19 days. [EPO] increased 64.2 ± 18.8% after 2 nights at altitude but was not different from baseline after 12 nights. Hb_mass and [EPO] did not increase in sea level. Reticulocytes (%) were slightly elevated in altitude at Days 5 and 12 (18.9 ± 17.7% and 20.4 ± 25.3%), sTfR was elevated at Day 12 (18.9 ± 15.0%), but both returned to baseline by Day 20. Hb_mass and [EPO] decreased on descent to sea level while ferritin increased. The mean increase in Hb_mass observed after 11 days (～300 h) of altitude training was beyond the measurement error and consitent with the mean increase after 300 h of simulated live high:train low altitude. Our results suggest that in elite cyclists, Hb_mass increases progressively with 3 weeks of natural altitude exposure, with greater increases expected as exposure persists.