Increased Ventilatory Efficiency in Supramaximal Compared to Graded Exercise in Athletes

<b>Background</b>: 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 ⩒_<i>E</i>-⩒CO₂ as ventilatory inefficiency. This misinterpretation could make difficult to differentiate between physiological hyperventilation from heart disease conditions in athletes. <b>Methods</b>: 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 <i>t</i>-Student statistics. <b>Results</b>: The ⩒_<i>E</i>-⩒CO₂ slope (31.4 ± 4.9 <i>vs</i>. 26.2 ± 3.4, <i>p</i> < .001), ⩒_<i>E</i>-⩒CO₂ intercept (7.2 ± 7.5 <i>vs</i>. 2.8 ± 4.2, <i>p</i> < .007), ⩒_<i>E</i>/⩒CO₂ nadir (33.0 ± 3.6 <i>vs</i>. 25.4 ± 2.2, <i>p</i> < .001), ⩒CO₂-log⩒_<i>E</i> slope (10.8 ± 2.9 <i>vs</i>. 6.9 ± 2.2 L_*logL^-1, <i>p</i> < .001), and η⩒^<i>E</i> (36.0 ± 12 <i>vs</i>. 22.8 ± 8.1%, <i>p</i> < .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 ⩒_<i>E</i>/⩒CO₂ nadir (coefficient of determination ~ 27%) and time to exhaustion. <b>Conclusions</b>: 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 ⩒_<i>E</i>-⩒CO₂ slope and ⩒_<i>E</i>/⩒CO₂ nadir indices, which may be confounded with ventilatory inefficiency. This study suggests that ventilatory changes underpin better ventilatory efficiency during CWR.