Is the Ventilatory Efficiency in Endurance Athletes Different?-Findings from the NOODLE Study

Background: Ventilatory efficiency (VE/VCO₂) is a strong predictor of cardiovascular diseases and defines individuals' responses to exercise. Its characteristics among endurance athletes (EA) remain understudied. In a cohort of EA, we aimed to (1) investigate the relationship between different methods of calculation of VE/VCO₂ and (2) externally validate prediction equations for VE/VCO₂. Methods: In total, 140 EA (55% males; age = 22.7 ± 4.6 yrs; BMI = 22.6 ± 1.7 kg·m^-2; peak oxygen uptake = 3.86 ± 0.82 L·min^-1) underwent an effort-limited cycling cardiopulmonary exercise test. VE/VCO₂ was first calculated to ventilatory threshold (VE/VCO₂-slope), as the lowest 30-s average (VE/VCO₂-Nadir) and from whole exercises (VE/VCO₂-Total). Twelve prediction equations for VE/VCO₂-slope were externally validated. Results: VE/VCO₂-slope was higher in females than males (27.7 ± 2.6 vs. 26.1 ± 2.0, p < 0.001). Measuring methods for VE/VCO₂ differed significantly in males and females. VE/VCO₂ increased in EA with age independently from its type or sex (β = 0.066-0.127). Eleven equations underestimated VE/VCO₂-slope (from -0.5 to -3.6). One equation overestimated VE/VCO₂-slope (+0.2). Predicted and observed measurements differed significantly in nine models. Models explained a low amount of variance in the VE/VCO₂-slope (R² = 0.003-0.031). Conclusions: VE/VCO₂-slope, VE/VCO₂-Nadir, and VE/VCO₂-Total were significantly different in EA. Prediction equations for the VE/VCO₂-slope were inaccurate in EA. Physicians should be acknowledged to properly assess cardiorespiratory fitness in EA.