Increased Ventilatory Efficiency in Supramaximal Compared to Graded Exercise in Athletes

Background: Supramaximal constant work rate tests (CWR) elicit intense hyperventilation, thus potentially up-shifting ventilation (⩒_E)-to-carbon dioxide (CO₂) responses when compared to graded exercise tests (GXT) in athletes. We predicted higher ventilatory efficiency on supramaximal CWR using a new method, challenging the classic orthodox interpretation of an increased ⩒_E-⩒CO₂ as ventilatory inefficiency. This misinterpretation could make difficult to differentiate between physiological hyperventilation from heart disease conditions in athletes. Methods: On different days, a GXT and a CWR at 110% of the maximal velocity achieved in the GXT were performed. Twenty-seven athletes completed the two tests and were compared for usual (linear regression) and log-transformed new variables for ventilatory efficiency through paired t-Student statistics. Results: The ⩒_E-⩒CO₂ slope (31.4 ± 4.9 vs. 26.2 ± 3.4, p < .001), ⩒_E-⩒CO₂ intercept (7.2 ± 7.5 vs. 2.8 ± 4.2, p < .007), ⩒_E/⩒CO₂ nadir (33.0 ± 3.6 vs. 25.4 ± 2.2, p < .001), ⩒CO₂-log⩒_E slope (10.8 ± 2.9 vs. 6.9 ± 2.2 L_*logL^-1, p < .001), and η⩒^E (36.0 ± 12 vs. 22.8 ± 8.1%, p < .001) values were all significantly higher in the CWR compared to the GXT. We registered a bi-modal nadir response for ⩒_E/⩒CO₂ on CWR for 22 out of 27 subjects for the first time. A weak association was observed between ⩒_E/⩒CO₂ nadir (coefficient of determination ~ 27%) and time to exhaustion. Conclusions: The new method allows us to improve the quantification and interpretation of ventilatory efficiency in athletes, avoiding misinterpretation due to the up-shifting elicited by the usual ⩒_E-⩒CO₂ slope and ⩒_E/⩒CO₂ nadir indices, which may be confounded with ventilatory inefficiency. This study suggests that ventilatory changes underpin better ventilatory efficiency during CWR.