Exercise above the maximal lactate steady state does not elicit a VO2 slow component that leads to attainment of VO2max

There is a pervasive belief that the severe intensity domain is defined as work rates above the power associated with a maximal lactate steady state (MLSS) and by a VO2 response that demonstrates a rapid increase (primary phase) followed by a slower increase (slow component), which leads to VO2max if exercise is continued long enough. Fifteen university students performed five to seven tests to calculate power at MLSS (154 ± 29 W). The tests included 30 minutes of exercise at each of three work rates: (i) below (-2 ± 1 W) power at MLSS, (ii) above (+4 ± 1 W) the power at MLSS, and (iii) well above (+19 ± 8 W) power at MLSS. The VO2 response in each test was described using mathematical modeling. Contrary to expectation, the response at the supra-MLSS work rates had not two, but three, distinct phases: the primary phase and the slow component, plus a "delayed" third phase, which emerged after ~15 minutes. VO2max was not attained at supra-MLSS work rates. These results challenge commonly held beliefs about definitions and descriptions of exercise intensity domains. Novelty • the VO2 response at work rates that are too high to sustain a lactate steady state but not high enough to elicit VO2max features not two, but three, distinct phases • there is not consensus whether intensity domains should be defined by their boundaries or by the responses they engender.