Background This study used a novel protocol to test the hypothesis that a plateau in oxygen consumption (VO2max) during incremental exercise testing to exhaustion represents the maximal capacity of the cardiovascular system to transport oxygen.
Methods Twenty-six subjects were randomly divided into two groups matched by their initial VO2max. On separate days, the reverse group performed (i) an incremental uphill running test on a treadmill (INC1) plus verification test (VER) at a constant workload 1 km h−1 higher than the last completed stage in INC1; (ii) a decremental test (DEC) in which speed started as same as the VER but was reduced progressively and (iii) a final incremental test (INCF). The control group performed only INC on the same days that the reverse group was tested.
Results VO2max remained within 0.6 ml kg−1 min−1 across the three trials for the control group (p=0.93) but was 4.4% higher during DEC compared with INC1 (63.9±3.8 vs 61.2±4.8 ml kg−1 min−1, respectively, p=0.004) in the reverse group, even though speed at VO2max was lower (14.3±1.1 vs 16.2±0.7 km h−1 for DEC and INC1, respectively, p=0.0001). VO2max remained significantly higher during INCF (63.6±3.68 ml kg−1 min−1, p=0.01), despite an unchanged exercise time between INC1 and INCF.
Conclusion These findings go against the concept that a plateau in oxygen consumption measured during the classically described INC and VER represents a systemic limitation to oxygen use. The reasons for a higher VO2 during INCF following the DEC test are unclear.
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