Kontro, H.; McGlory, C.; MacInnis, M.

Aim: Compare the fractional synthetic rate (FSR) of hemoglobin in trained and untrained humans (Hb FSR). Methods: We employed deuterated water (2H2O) to measure Hb FSR in young males (n=10) and females (n=10) who were aerobically trained (n=5 per sex) and untrained (n=5 per sex). Overall, participants had a mean [V]O2max of 49.8 [SD: 10.9] mL/kg/min, hemoglobin mass of 775 [180] g, and red blood cell volume of 2370 [550] mL. After an initial loading dose, participants ingested 2H2O daily for 28 days to maintain a stable 2H body water enrichment (~0.9 atom percent deuterium (APD)), as measured in saliva samples collected every 2-3 days. 2H-enriched alanine was measured in RBC protein using gas chromatography combustion isotope ratio mass spectrometry. Results: The increase in APD for Hb protein was nonlinear for the first two weeks, but stabilized from day 14 to day 28, with mean APD reaching 0.033 [0.005] % on day 28. Hb FSR calculated over this 2-week period was 0.84 [0.15] %/day, which equated to an Hb absolute synthetic rate of 6.5 [2.2] g/day and a lifespan of 126 [30] days. Hb FSR was not different trained (0.83 [0.19] %/day) and untrained (0.86 [0.24] %/day, P=0.81) individuals or between males (0.80 [0.25] %/day) and females (0.88 [0.17] %/day), P=0.24). Conclusion: Habitual endurance training does not appear to affect Hb FSR, but the use of 2H2O to measure Hb FSR in humans has potential applications to many experimental and clinical scenarios.