Strenuous physical training increases total blood volume (BV) through expansion of plasma (PV) and red cell volumes (RCV). In contrast, exogenous erythropoietin (EPO) treatment increases RCV but decreases PV, rendering BV stable or slightly decreased. This study aimed to determine the combined effects of strenuous training and EPO treatment on BV and markers of systemic and muscle iron homeostasis. In this longitudinal study, 8 healthy non-anemic males were treated with EPO (50 IU/kg body mass, 3x/week, subcutaneously) across 28 days of strenuous training (4d/week, exercise energy expenditures of 1334±24 kcal/d) while consuming a controlled, energy-balanced diet providing 39±4 mg/d iron. Before (PRE) and after (POST) intervention, BV compartments were measured using carbon monoxide rebreathing, and markers of iron homeostasis were assessed in blood and skeletal muscle (vastus lateralis). Training + EPO increased (p<0.01) RCV (13±6%) and BV (5±4%), whereas PV remained unchanged (p=0.86). The expansion of RCV was accompanied by a large decrease in whole-body iron stores, as indicated by decreased (p<0.01) ferritin (-77±10%) and hepcidin (-49±23%) concentrations in plasma. Training + EPO decreased (p<0.01) muscle protein abundance of ferritin (-25±20%) and increased (p<0.05) transferrin receptor (47±56%). These novel findings illustrate that strenuous training combined with EPO results in both increased total oxygen carrying capacity and hypervolemia in young healthy males. The decrease in plasma and muscle ferritin suggests that the marked upregulation of erythropoiesis alters systemic and tissue iron homeostasis, resulting in a decline in whole-body and skeletal muscle iron stores.
Keywords: Blood Volume; Erythropoietin; Exercise Training; Iron Homeostasis.