Curvilinear VO₂:Power Output Relationship in a Ramp Test in Professional Cyclists: Possible Association with Blood Hemoglobin Concentration

Abstract

The purpose of this study was to determine (1) if there exists an additional, nonlinear increase (ΔVO₂) in the oxygen uptake observed (VO_{2 obs}) at the maximal power output reached during a ramp cycle ergometer test and that expected (VO_{2 exp}) from the linear relationship between VO₂ and power output below the lactate threshold (LT) in professional riders, and (2) the relationship between ΔVO₂ and possible explanatory mechanisms. Each of 12 professional cyclists (25 ± 1 years; VO_{2 max}: 71.3 ± 1.2 ml·kg⁻¹·min⁻¹) performed a ramp test until exhaustion (power output increases of 25 W·min⁻¹) during which several gas-exchange and blood variables were measured (including lactate, HCO₃⁻ and K⁺). VO₂ was linearly related to power output until the LT in all subjects. Afterward, a nonlinear deflection was observed in the VO₂:power output relationship (ΔVO₂ = 2492 ± 55 ml·min⁻¹ and p < 0.05 for VO_{2 obs} vs. VO_{2 exp}). A significant negative correlation was encountered between ΔVO₂ and resting hemoglobin levels before the tests (r = 20.61; p < 0.05). In conclusion, professional cyclists exhibit an attenuation of the VO₂ rise above the LT.