BACKGROUND: The purpose of this study was to analyze cardiac output (Qc), stroke volume (SV), heart rate (HR), and arterio-venous O2 difference (a-vO2diff) responses throughout a graded exercise test (GXT) and verification phase (VP) to examine whether SV decrement during the GXT is a main factor for underestimation of the maximal O2 uptake (VO2max), or not. METHODS: Seven well-trained male cyclists volunteered for this study (VO2max: 61.7±6.13 mL/min/kg). Following submaximal tests, participants were asked to perform GXT until exhaustion. Then, multisession verifications were performed on different days using ±3% constant work rates. The highest 30-second mean of VO2 was considered as the VO2max and corresponding external power as peak power output (PPO). The Qc, SV, HR, and a-vO2diff responses were evaluated at both GXT and VP by nitrous-oxide rebreathing method. After repeated-measures analyses, possible significant differences were investigated by LSD/Wilcoxon. RESULTS: It was shown that the HR and a-vO2diff reached their potentially highest values at the end of the both GXT and VP (192.9±8.8 vs. 190.7±7.9 bpm; 17.1±1.6 vs. 16.9±1.1%, respectively; P>0.05); however, SV (128.8±11.2 vs. 137.3±11.2 mL; P=0.029) and Qc (24.8±2.02 vs. 26.2±2.71 L/min; P=0.046) were lower at GXT when compared to the VP. VO2 means were, therefore, higher in VP when compared to the GXT (61.7±6.13 vs. 59.1±6.2 mL/min/kg; P=0.041). CONCLUSIONS: The GXT provided only a peak VO2 but not the VO2max. Consequently, the real VO2max and PPO could be provided by only VP administrations. This is likely to result from the lower Qc and SV responses observed from a prolonged incremental test protocol when compared to short bouts of constant work rate trials.
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