Critical speed, thresholds for vo2max and boundaries of the severe exercise intensity domain

ABSTRACT Introduction: The severe exercise intensity domain can be defined as the range of work rates or speeds over which VO2max can be elicited. Objectives: Our purpose was to determine if critical speed (running analog of critical power) identifies the lower boundary of the severe domain and to identify the upper boundary of the domain. Methods: Twenty-five individuals performed five running tests to exhaustion, each lasting > 2.5 min and < 16 min. The two-parameter speed vs time-to-exhaustion relationship generated values for critical speed and the three-parameter speed vs time-to-reach-VO2max relationship generated values for the threshold speed above which VO2max can be elicited. The relationships were solved to calculate the minimum time needed to elicit VO2max. Results: Critical speed (3.00 ± 0.38 m·s−1) and the threshold speed above which VO2max can be elicited (2.99 ± 0.37 m·s−1) were correlated (r = 0.83, p < 0.01) and did not differ (p = 0.70), confirming critical speed as the lower boundary of the severe domain. The minimum time needed to elicit VO2max (103 ± 7 s) and the associated highest speed at which VO2max can be elicited (4.98 ± 0.52 m·s−1) identified the upper boundary of the severe domain for these participants. Conclusion: The critical power concept, which requires no metabolic measurements, can be used to identify the lowest speed at which VO2max can be elicited. With addition of metabolic measurements, mathematical modeling can also identify the highest speed and shortest exercise duration at which VO2max can be elicited. Evidence Level I; Validating cohort study with good reference standards.