Erythropoiesis with endurance training: dynamics and mechanisms.
Level 4 - case-series / case-control
Prospective single-arm before-and-after interventional study without a control group
PubMed 28381454 · doi:10.1152/ajpregu.00012.2017
What was done
Nine healthy, untrained volunteers (mean age 27 ± 4 years) completed 8 weeks of supervised endurance cycling (3–4 sessions of 60 minutes per week). Researchers measured plasma volume (PV), red blood cell volume (RBCV), and fasting hematological markers at baseline and at weeks 2, 4, and 8. In addition, plasma erythropoietin (EPO), cortisol, copeptin, and proatrial natriuretic peptide concentrations were assessed during a 3-hour morning period at baseline and post-exercise at weeks 1 and 8.
What was found
Plasma volume expanded from baseline (2,405 ± 335 ml) at week 2 (+374 ± 194 ml), week 4 (+505 ± 156 ml), and week 8 (+341 ± 160 ml; P < 0.001 for all). Red blood cell volume increased from baseline (1,737 ± 442 ml) at week 4 (+109 ± 114 ml, P = 0.030) and week 8 (+205 ± 109 ml, P = 0.001). Overnight fasting EPO increased from baseline (11.3 ± 4.8 mIU/ml) at week 2 (+2.5 ± 2.8 mIU/ml, P = 0.027) and returned to baseline at weeks 4 and 8. Three-hour post-exercise EPO was higher at week 1 (11.6 mIU/ml) than at baseline (9.0 ± 4.2 mIU/ml, P = 0.019) and week 8 (8.4 ± 3.9 mIU/ml, P = 0.009). EPO levels inversely correlated with hematocrit (β = -56.2, P < 0.001) and positively correlated with cortisol (β = 0.037, P < 0.001).
Why it matters
This study outlines the temporal sequence of hematological adaptations to exercise, showing that plasma volume expands rapidly and transiently elevates EPO (likely via hemodilution-induced reductions in hematocrit) prior to the slower expansion of red blood cell volume.
Limits
The sample size is very small (n = 9), and there was no non-exercising control group to rule out confounding temporal variations. Participant sex distribution is not reported in the abstract, and findings in young untrained adults may not generalize to elite athletes or clinical cohorts. Specific numerical results for copeptin and proatrial natriuretic peptide were omitted from the abstract.