Erythropoiesis with endurance training: dynamics and mechanisms.

The purpose of the present study was to characterize the progression of red blood cell volume (RBCV) expansion and potential volumetric and endocrine regulators of erythropoiesis during endurance training (ET). Nine healthy, untrained volunteers (age = 27 ± 4 yr) underwent supervised ET consisting of 3-4 × 60 min cycle ergometry sessions per week for 8 wk. Plasma volume (PV), RBCV, and overnight fasting hematological markers were determined before and at , , and of ET. In addition, plasma erythropoietin (EPO), cortisol, copeptin, and proatrial natriuretic peptide concentrations were measured during a 3-h morning period at baseline and postexercise at and PV increased from baseline (2,405 ± 335 ml) at , , and (+374 ± 194, +505 ± 156, and +341 ± 160 ml, respectively, < 0.001). Increases in RBCV from baseline (1,737 ± 442 ml) were manifested at (+109 ± 114 ml, = 0.030) and (+205 ± 109 ml, = 0.001). Overnight fasting plasma EPO concentration increased from baseline (11.3 ± 4.8 mIU/ml) at (+2.5 ± 2.8 mIU·ml, = 0.027) and returned to baseline concentration at and Higher 3-h-postexercise EPO concentration was observed at (11.6 mIU/ml) compared with (8.4 ± 3.9 mIU/ml, = 0.009) and baseline (9.0 ± 4.2 mIU/ml, = 0.019). Linear relationships between EPO concentration and hematocrit (β = -56.2, < 0.001) and cortisol (β = 0.037, < 0.001) were detected throughout the ET intervention. In conclusion, ET leads to mild, transient increases in circulating EPO concentration, concurring with early PV expansion and lowered hematocrit, preceding gradual RBCV enhancement.