IS THE EXHAUSTION TIME AT MAXIMAL AEROBIC SPEED AS INDEX OF AEROBIC ENDURANCE

The velocity of the last stage of the Montreal Track Test (MTT) has be en measured in fifteen well trained runners. This velocity (vMTT) was assumed to be close to maximal aerobic running speed. In three differe nt sessions, the subjects ran up to exhaustion at velocities correspon ding to 95, 100 and 105 % vMTT. The exhaustion time at 100 % vMTT (t(l im)100) was assumed to be an estimation of the exhaustion time corresp onding to maximal aerobic speed. The relationship between exhaustion t ime (t(lim)) and distance (D-lim) in the case of running exercises at constant velocity until exhaustion can be described by a linear relati onship (D-lim = D + bt(lim)). The slope of the relation corresponds t o a velocity (v(crit)) which can be sustained for a long time. The val ues of V-crit were calculated from the results of running exercises pe rformed at 95, 100 and 105 % of vMTT. The present study showed that tl im at 100 % vMTT (t(lim)100) was negatively correlated with vMTT and v (crit) but that D and ratio v(crit)/vMTT were independent of vMTT. A t heoretical study based on models previously proposed for oxygen kineti cs during supramaximal exercises (exponential model and Margaria's mod el) demonstrates that this negative relationship between vMTT and t(li m)100 can be explained by the kinetics of the accumulation of oxygen d eficit (O(2)def). t(lim)100 should also depend on VO(2)max, maximal ox ygen deficit (Max O-2 def) and the relative importance of anaerobic en ergy when a VO2 plateau is reached. Moreover, the value of t(lim)100 l argely depends an the accuracy of the assessment of vMTT. Consequently , the exhaustion times corresponding to the different estimations of m aximal aerobic speed on a track or a treadmill cannot be considered as valid indices of aerobic endurance.