High Intraindividual Variability in the Response of Serum Erythropoietin to Multiple Simulated Altitude Exposures

Baranauskas, Marissa N., Timothy J. Fulton, Alyce D. Fly, Bruce J. Martin, Timothy D. Mickleborough, and Robert F. Chapman. High intraindividual variability in the response of serum erythropoietin to multiple simulated altitude exposures. High Alt Med Biol. 23:85-89, 2022. To evaluate within-subject variability in the serum erythropoietin (EPO) response to multiple simulated altitude exposures. Seven physically active men and women (age 27 ± 3 years, body mass index = 24.6 ± 4.0 kg/m²) were exposed to normobaric hypoxia (fraction of inspired oxygen [F_iO₂] = 0.14) for 12 hours on three separate occasions. Serum EPO concentrations were measured before exposure (0 hour), after 6 hours, and after 12 hours in hypoxia. The EPO response to hypoxia was calculated as percent change from 0 to 12 hours (ΔEPO_0-12). Exposure time had a significant effect on EPO (p < 0.001) with concentrations increasing 3.2 ± 1.3 mIU/ml from 0 to 6 hours (p = 0.034) and 4.7 ± 1.2 mIU/ml from 0 to 12 hours (p = 0.001). Group mean ΔEPO_0-12 remained unchanged (p = 0.688) between the three exposures; however, there was considerable intraindividual variability in EPO responses. The intrasubject coefficient of variation for ΔEPO_0-12 was 61% ± 28% (range: 17%-103%) with intrasubject associations ranging r = 0.052 to r = 0.651 between repeated exposures. Athletes who routinely supplement training with simulated altitude methods (e.g., hypoxic tents) should expect inconsistent EPO responses to intermittent exposures lasting ≤12 hours.