Background: Blood volume (BV), haemoglobin mass (Hb-mass) are key determinants of blood oxygen transport. The aim of this study was to assess BV and Hb-mass in elite junior rowers and evaluate their relationship with fat-free mass (FFM) and aerobic capacity. Methods: Twenty-five males (18.4 ± 2.4 y, 1.92 ± 0.5 m, 89.3 ± 4.7 kg) and fourteen females (17.0 ± 1.9 y, 1.77 ± 0.7 m, 74.2 ± 11.3 kg) participated. BV, plasma volume (PV), and Hb-mass were assessed via CO rebreathing. Pulmonary gas exchange was measured during a graded rowing test. Results: Males had higher absolute BV (7270 ± 717 vs. 5388 ± 471 mL) and Hb-mass (1083 ± 91 vs. 720 ± 49 g). After adjusting for FFM, most differences disappeared, except PV, which remained higher in females (57.2 ± 4.8 vs. 49.9 ± 6.5 mL·FFM·kg-1). VO2max was higher in males in absolute (6.28 ± 0.40 vs. 4.48 ± 0.29 L·min-1) and body-mass-relative terms (70.2 ± 5.6 vs. 61.3 ± 7.3 mL·kg-1·min-1), but not when expressed per FFM (79.4 ± 5.3 vs. 81.1 ± 7.3 mL·FFM·kg-1·min-1). BV, PV, and Hb-mass correlated positively with VO2max in both sexes, with stronger associations in females. Conclusions: Sex differences in blood parameters among junior rowers are largely explained by FFM, except for PV, which is relatively higher in females. Stronger associations between blood variables and aerobic capacity in females suggest greater reliance on central oxygen transport.
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