The sustainability of VO2max: effect of decreasing the workload.

The study examined the maintenance of VO2max using VO2max as the controlling variable instead of power. Therefore, ten subjects performed three exhaustive cycling exercise bouts: (1) an incremental test to determine VO2max and the minimal power at VO2max (PVOmax), (2) a constant-power test at PVOmax and (3) a variable-power test (VPT) during which power was varied to control VO2 at VO2max. 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 PVOmax (238 ± 79 vs. 305 ± 86 W; p < 0.0001). All subjects, regardless of their VO2max values and/or their ability to achieve a VO2max plateau during incremental test, were able to sustain VO2max 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 VO2max during VPT was correlated with the power drop in the first quarter of the time to exhaustion at VO2max (r = 0.71; p < 0.02) and with the stroke volume reserve (r = 0.70, p = 0.02) but was not correlated with VO2max. This protocol, using VO2max rather than power as the controlling variable, demonstrates that the maintenance of exercise at VO2max can exceed 15 min independent of the VO2max value, suggesting that the ability to sustain exercise at VO2max has different limiting factors than those related to the VO2max value.