Intra-individual Variability In The Acute Erythropoietic Response To Consecutive Hypoxic Exposures

Abstract

PURPOSE: Altitude training has become a standard strategy used by athletes to legitimately increase hemoglobin mass and induce favorable changes in sea-level endurance performance. While the acute erythropoietic response to a fixed level of hypoxia (altitude) varies considerably between individuals, it is generally assumed there is consistency within an individual for repeated exposures. Therefore, we aimed to document within-subject variation in the acute erythropoietic response to consecutive exposures to a fixed-level of continuous normobaric hypoxia. METHODS: Seven subjects (men n = 4, women n = 3) completed three exposures to 12hr of continuous normobaric hypoxia simulating an altitude of 3,000m/9,900ft (FiO2 = 0.14), with each exposure separated by 28 to 56 days. Each visit was performed at the same time of day, with close controls placed on hydration and environmental conditions. Serum concentrations of erythropoietin (EPO) were measured at baseline prior to hypoxic exposure (0hr), and then following 6hr, and 12hr spent in continuous hypoxia. The relative change in serum EPO was taken as the percentage difference from 0hr to 6hr (ΔEPO0-6) and 0hr to 12hr (ΔEPO0-12). A two-way repeated measures ANOVA was used to evaluate the effects of hypoxic exposure time on EPO concentrations. RESULTS: Twelve hours of continuous hypoxic exposure had a significant effect on the EPO response (P < 0.001), with serum concentrations increasing by an average of +55 ± 33% (range: 14-110%) after 6hr and +83 ± 33% (range: 31-125%) after 12hr compared to baseline. Within individuals, ΔEPO0-6 varied by 33 ± 23% (range: 4- 77%) and ΔEPO0-12 by 58 ± 28% (range: 4-90%) between consecutive hypoxic exposures. CONCLUSIONS: Practically, our data demonstrate that athletes traveling to altitude training camps may not have a consistent hematological response given the wide intra-individual variability observed in serum EPO concentrations to repeated fixed hypoxic doses.