Vo2 kinetics and the O2 deficit in heavy exercise

The purpose of this study was to examine a new method for calculating the O-2 deficit that considered the O-2 uptake ((V) over dot O-2) kinetics during exercise as two separate phases in light of previous research in which it was shown that the traditional O-2 deficit calculation overestimated the recovery O-2 consumption (ROC). Eight subjects completed exercise transitions between unloaded cycling and 25% (heavy, H) or 50% (very heavy, VH) of the difference between the lactic acid threshold (LAT) and peak (V) over dot O-2 for 8 min. The O-2 deficit, calculated in the traditional manner, was significantly greater than the measured ROC for both above-LAT exercises: 4.03 +/- 1.01 vs. 2.63 +/- 0.80 (SD) liters for VH and 2.36 +/- 0.91 vs. 1.74 +/- 0.63 liters for H for the O-2 deficit vs. ROC (P < 0.05). When the kinetics were viewed as two separate components with independent onsets, the calculated O-2 deficit (2.89 +/- 0.79 and 1.71 +/- 0.70 liters for VH and H, respectively) was not different from the measured ROC (P < 0.05). Subjects also performed the same work rate for only 3 min. These data, from bouts terminated before the slow component could contribute appreciably to the overall (V) over dot O-2 response, show that the O-2 requirement during the transition is less than the final steady state for the work rate, as evidenced by symmetry between the O-2 deficit and ROC. This new method of calculating the O-2 deficit more closely reflects the expected O-2 deficit-ROC relationship (i.e., ROC greater than or equal to O-2 deficit). Therefore, estimation of the O-2 deficit during heavy exercise transitions should consider the slow component of (V) over dot O-2 as an additional deficit component with delayed onset.