The sustainability of VO_2max: effect of decreasing the workload

The study examined the maintenance of VO_2max using VO_2max as the controlling variable instead of power. Therefore, ten subjects performed three exhaustive cycling exercise bouts: (1) an incremental test to determine VO_2max and the minimal power at VO_2max (PVO_max), (2) a constant-power test at PVO_max and (3) a variable-power test (VPT) during which power was varied to control VO₂ at VO_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_max (238 ± 79 vs. 305 ± 86 W; p < 0.0001). All subjects, regardless of their VO_2max values and/or their ability to achieve a VO_2max plateau during incremental test, were able to sustain VO_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_2max during VPT was correlated with the power drop in the first quarter of the time to exhaustion at VO_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_2max. This protocol, using VO_2max rather than power as the controlling variable, demonstrates that the maintenance of exercise at VO_2max can exceed 15 min independent of the VO_2max value, suggesting that the ability to sustain exercise at VO_2max has different limiting factors than those related to the VO_2max value.