Oxygen uptake efficiency plateau is unaffected by fitness level - the NOODLE study

Endurance athletes (EA) are an emerging population of focus for cardiovascular health. The oxygen uptake efficiency plateau (OUEP) is the levelling-off period of ratio between oxygen uptake (VO₂) and ventilation (VE). In the cohort of EA, we externally validated prediction models for OUEP and derived with internal validation a new equation.

140 EA underwent a medical assessment and maximal cycling cardiopulmonary exercise test. Participants were 55% male (N = 77, age = 21.4 ± 4.8 years, BMI = 22.6 ± 1.7 kg·m^- 2, peak VO₂ = 4.40 ± 0.64 L·min^- 1) and 45% female (N = 63, age = 23.4 ± 4.3 years, BMI = 22.1 ± 1.6 kg·m^- 2, peak VO₂ = 3.21 ± 0.48 L·min^- 1). OUEP was defined as the highest 90-second continuous value of the ratio between VO₂ and VE. We used the multivariable stepwise linear regression to develop a new prediction equation for OUEP.

OUEP was 44.2 ± 4.2 mL·L^- 1 and 41.0 ± 4.8 mL·L^- 1 for males and females, respectively. In external validation, OUEP was comparable to directly measured and did not differ significantly. The prediction error for males was - 0.42 mL·L^- 1 (0.94%, p = 0.39), and for females was + 0.33 mL·L^- 1 (0.81%, p = 0.59). The developed new prediction equation was: 61.37-0.12·height (in cm) + 5.08 (for males). The developed model outperformed the previous. However, the equation explained up to 12.9% of the variance (R = 0.377, R² = 0.129, RMSE = 4.39 mL·L^- 1).

OUEP is a stable and transferable cardiorespiratory index. OUEP is minimally affected by fitness level and demographic factors. The predicted OUEP provided promising but limited accuracy among EA. The derived new model is tailored for EA. OUEP could be used to stratify the cardiorespiratory response to exercise and guide training.