Background: This study used a novel protocol to test the hypothesis that a plateau in oxygen consumption (VO(2 max)) 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 VO(2 max). On separate days, the reverse group performed (i) an incremental uphill running test on a treadmill (INC(1)) plus verification test (VER) at a constant workload 1 km h(-1) higher than the last completed stage in INC(1); (ii) a decremental test (DEC) in which speed started as same as the VER but was reduced progressively and (iii) a final incremental test (INC(F)). The control group performed only INC on the same days that the reverse group was tested.
Results: VO(2 max) 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 INC(1) (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 VO(2 max) was lower (14.3 ± 1.1 vs 16.2 ± 0.7 km h(-1) for DEC and INC(1), respectively, p=0.0001). VO(2 max) remained significantly higher during INC(F) (63.6 ± 3.68 ml kg(-1) min(-1), p=0.01), despite an unchanged exercise time between INC(1) and INC(F).
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 VO(2) during INC(F) following the DEC test are unclear.