Oxygen kinetics during continuous running at critical velocity

The purpose of this study was twofold: (1) to determine if there were differences in critical velocity (CV) estimates from five mathematical models; and (2) to examine the oxygen kinetics during continuous treadmill runs at the five estimates of CV. Ten adult subjects (six males and four females) performed one incremental test to determine maximal oxygen consumption rate (V˙O2max) and four or five randomly ordered constant velocity trials on a treadmill for the estimation of CV. Five mathematical models were used to estimate CV for each subject including two linear (Lin-TD and Lin-V), two nonlinear (Non-3 and Non-2), and an exponential model (EXP). Up to five randomly ordered continuous runs were performed by each subject at treadmill velocities that corresponded to the five CV estimates. Oxygen consumption (V˙O2) and heart rate (HR) were monitored throughout the continuous runs. The results of the present investigation indicated that the Non-3 model produced CV estimates that were significantly (p \u3c 0.05) less than the other four models. Five of the subjects, however, did not complete 60 min of running at CV from the Non-3 model (mean time to exhaustion (Terra): 43.4 ± 14.2 min; range 18.5 to 50.4 min). Furthermore, V˙O2 kinetics indicated that mean V˙O2 increased (from the 3rd min of exercise to Tend) during the continuous runs at CV for all five models and that the mean V˙O2 increases (range = 367 to 458 ml•min−1) were substantially greater than that typically associated with O2drift (≈200 ml•min −1). The mean V˙O2 at exhaustion (V˙O 2end) values of the continuous runs at CV, however, were significantly less than V˙O2max for all five mathematical models. The results of the present study indicated that the Non-3 model produced the lowest estimates of CV, and that the intensity of exercise associated with CV from all five models was in the heavy exercise domain