The Influence of Oxygen Saturation on the Relationship Between Hemoglobin Mass and VO ₂ max

Hemoglobin mass (tHb) is a key determinant of maximal oxygen uptake (VO ₂ max). We examined whether oxyhemoglobin desaturation (ΔS _a O ₂ ) at VO ₂ max modifies the relationship between tHb and VO ₂ max at moderate altitude (1,625 m). Seventeen female and 16 male competitive, endurance-trained moderate-altitude residents performed two tHb assessments and two graded exercise tests on a cycle ergometer to determine VO ₂ max and ΔS _a O ₂ . In males and females respectively, VO ₂ max (ml·kg ^-1 ·min ^-1 ) ranged from 62.5-83.0 and 44.5-67.3; tHb (g·kg ^-1 ) ranged from 12.1-17.5 and 9.1-13.0; and S _a O ₂ at VO ₂ max (%) ranged from 81.7-94.0 and 85.7-95.0. tHb was related to VO ₂ max when expressed in absolute terms and after correcting for body mass (r=0.94 and 0.86, respectively); correcting by ΔS _a O ₂ did not improve these relationships (r=0.93 and 0.83). Additionally, there was a negative relationship between tHb and S _a O ₂ at VO ₂ max (r=-0.57). In conclusion, across a range of endurance athletes at moderate altitude, the relationship between tHb and VO ₂ max was found to be similar to that observed at sea level. However, correcting tHb by ΔS _a O ₂ did not explain additional variability in VO ₂ max despite significant variability in ΔS _a O ₂ ; this raises the possibility that tHb and exercise-induced ΔS _a O ₂ are not independent in endurance athletes.