Plasma volume reduction and hematological fluctuations in high‐level athletes after an increased training load

The time course of plasma volume ( PV ) reduction following an increased training load period is unknown and was investigated. The accompanying fluctuations in [Hb] and OFF ‐hr score were analyzed in the Athlete Biological Passport. Further, whether fluctuations in plasma albumin, soluble transferrin receptors ( sTfR ), and pro‐atrial natriuretic peptide (pro ANP ) concentrations correlate with PV fluctuations was investigated. Eleven high‐level competitive cyclists were investigated for 3 weeks. After initial measurements in week 1, training load was increased ~250% in week 2 followed by a reversion to baseline training load in week 3. PV and hematological variables were determined frequently during all weeks. The higher training load in week 2 increased ( P <.001) PV 10%, while [Hb] and OFF ‐hr score decreased ~6% ( P <.01) and ~16% ( P <.001), respectively. PV and [Hb] returned to baseline within 2 and 4 days after week 2, respectively, while OFF ‐hr score remained reduced for 6 days. Further, one and three atypical blood profiles of the ABP occurred during weeks 2 and 3, respectively. Individual changes in albumin, sTfR , and pro ANP only correlated weakly ( R 2 <.20) with PV fluctuations. In conclusion, PV and [Hb] fluctuations caused by an elevated training load period were reverted within 2 and 4 days after returning to baseline training load, respectively, while OFF ‐hr remained altered for 6 days. Furthermore, some atypical blood profiles were induced during and subsequent to the increased training load, demonstrating the importance of knowledge on naturally occurring hematological fluctuations. Finally, concentrations of albumin, sTfR , and pro ANP could not explain PV fluctuations.