The sustainability of VO^sub 2max^: effect of decreasing the workload

The study examined the maintenance of VO^sub 2max^ using VO^sub 2max^ as the controlling variable instead of power. Therefore, ten subjects performed three exhaustive cycling exercise bouts: (1) an incremental test to determine VO^sub 2max^ and the minimal power at VO^sub 2max^ (PVO^sub max^), (2) a constant-power test at PVO^sub max^ and (3) a variable-power test (VPT) during which power was varied to control VO2 at VO^sub 2max^. Stroke volume (SV) was measured by impedance in each test and the stroke volume reserve was calculated as the difference between the maximal and the average 5-s SV. Average power during VPT was significantly lower than PVO^sub max^ (238 ± 79 vs. 305 ± 86 W; p < 0.0001). All subjects, regardless of their VO^sub 2max^ values and/or their ability to achieve a VO^sub 2max^ plateau during incremental test, were able to sustain VO^sub 2max^ for a significantly longer time during VPT compared to constant-power test (CPT) (958 ± 368 s vs. 136 ± 81 s; p < 0.0001). Time to exhaustion at VO^sub 2max^ during VPT was correlated with the power drop in the first quarter of the time to exhaustion at VO^sub 2max^ (r = 0.71; p < 0.02) and with the stroke volume reserve (r = 0.70, p = 0.02) but was not correlated with VO^sub 2max^. This protocol, using VO^sub 2max^ rather than power as the controlling variable, demonstrates that the maintenance of exercise at VO^sub 2max^ can exceed 15 min independent of the VO^sub 2max^ value, suggesting that the ability to sustain exercise at VO^sub 2max^ has different limiting factors than those related to the VO^sub 2max^ value.[PUBLICATION ABSTRACT]