Blood Volume, Hemoglobin Mass, and Peak Oxygen Uptake in Older Adults: The Generation 100 Study

Purpose: To investigate the association between blood volume, hemoglobin mass (Hb_mass), and peak oxygen uptake (VO_2peak) in healthy older adults. Methods: Fifty fit or unfit participants from the prospective randomized Generation 100 Study (n = 1,566) were included (age- and sex-specific VO_2peak above or below average values). Blood, plasma, and erythrocyte volume and Hb_mass were tested using the carbon monoxide rebreathing method within 1 week after VO_2peak testing. Results: Mean age, BMI, Hb_mass, blood volume, and VO_2peak were 73.0 ± 2.1 years, 24.8 ± 3.3 kg·m², 10.0 ± 1.7 g·kg^-1, 76.4 ± 11.8 mL·kg^-1, and 33.5 ± 8.4 mL·kg^-1·min^-1. VO_2peak in fit and unfit participants and women and men were 38.6 ± 6.5 and 25.8 ± 3.8 mL·kg^-1·min^-1, 30.7 ± 7.6 mL·kg^-1·min^-1, and 35.5 ± 8.5 mL·kg^-1·min^-1, respectively. Women were shorter (Δ14 cm), leaner (Δ13 kg), and with less muscle mass (Δ9%) than men (P < 0.05). Relative erythrocyte volume and Hb_mass were lower in women, and blood and erythrocyte volume and Hb_mass were higher in the fit participants (P < 0.05). Hb_mass and erythrocyte volume explained 40 and 37%, respectively, of the variability in VO_2peak, with a limited effect of physical-activity adjustment (40 and 38%, respectively). Blood and plasma volume explained 15 and 25%, respectively, of VO_2peak variability, and the association was strengthened adjusting for physical activity (25 and 31%, respectively), indicating a training-dependent adaptation in plasma but not erythrocyte volume (p ≤ 0.006). Conclusions: Blood and plasma volumes were moderately associated with VO_2peak in healthy older men and women, and the association was strengthened after adjustment for physical activity. Hb_mass and erythrocyte volume were strongly associated with VO_2peak but unrelated to physical activity.