Negative accumulated oxygen deficit during heavy and very heavy intensity cycle ergometry in humans

The concept of the accumulated O(2) deficit (AOD) assumes that the O(2) deficit increases monotonically with increasing work rate (WR), to plateau at the maximum AOD, and is based on linear extrapolation of the relationship between measured steady-state oxygen uptake ( VO(2)) and WR for moderate exercise. However, for high WRs, the measured VO(2) increases above that expected from such linear extrapolation, reflecting the superimposition of a "slow component" on the fundamental VO(2) mono-exponential kinetics. We were therefore interested in determining the effect of the VO(2) slow component on the computed AOD. Ten subjects [31 (12) years] performed square-wave cycle ergometry of moderate (40%, 60%, 80% and 90% ), heavy (40%Delta), very heavy (80%Delta) and severe (110% VO(2)(peak)) intensities for 10-15 min, theta(L)where is the estimated lactate threshold and Delta is the WR difference between and VO(2)(peak). VO(2) was determined breath-by-breath. Projected "steady-state" VO(2) values were determined from sub- tests. The measured VO(2) exceeded the projected value after approximately 3 min for both heavy and very heavy intensity exercise. This led to the AOD actually becoming negative. Thus, for heavy exercise, while the AOD was positive [0.63 (0.41) l] at 5 min, it was negative by 10 min [-0.61 (1.05) l], and more so by 15 min [-1.70 (1.64) l]. For the very heavy WRs, the AOD was [0.42 (0.67) l] by 5 min and reached -2.68 (2.09) l at exhaustion. For severe exercise, however, the AOD at exhaustion was positive in each case: +1.69 (0.39) l. We therefore conclude that the assumptions underlying the computation of the AOD are invalid for heavy and very heavy cycle ergometry (at least). Physiological inferences, such as the "anaerobic work capacity", are therefore prone to misinterpretation.