Is the Exhaustion Time at Maximal Aerobic Speed an Index of Aerobic Endurance?

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Abstract
The velocity of the last stage of the Montreal Track Test (MTT) has been measured in fifteen well trained runners. This velocity (νMTT) was assumed to be close to maximal aerobic running speed. In three different sessions, the subjects ran up to exhaustion at velocities corresponding to 95, 100 and 105 % νMTT. The exhaustion time at 100 % νMTT (tlim 100) was assumed to be an estimation of the exhaustion time corresponding to maximal aerobic speed. The relationship between exhaustion time (tlim) and distance (Dlim) in the case of running exercises at constant velocity until exhaustion can be described by a linear relationship (Dlim = D + b*tlim). The slope of the relation corresponds to a velocity (νcrit) which can be sustained for a long time. The values of νcrit were calculated from the results of running exercises performed at 95, 100 and 105 % of νMTT. The present study showed that tlim at 100 % νMTT (tlim100) was negatively correlated with νMTT and νcrit but that D and ratio νcrit/νMTT were independent of νMTT. A theoretical study based on models previously proposed for oxygen kinetics during supramaximal exercises (exponential model and Margaria’s model) demonstrates that this negative relationship between νMTT and tlim100 can be explained by the kinetics of the accumulation of oxygen deficit (O2 def). tlim100 should also depend on V̇O2max, maximal oxygen deficit (Max O2 def) and the relative importance of anaerobic energy when a V̇O2 plateau is reached. Moreover, the value of tlim100 largely depends on the accuracy of the assessment of νMTT. Consequently, the exhaustion times corresponding to the different estimations of maximal aerobic speed on a track or a treadmill cannot be considered as valid indices of aerobic endurance.