The Increase in Oxygen Demand During Severe Intensity Exercise Must be Included in Calculation of Oxygen Deficit

A contentious element in the traditional method of calculating accumulated oxygen deficit (AOD) is the assumption that the oxygen demand remains constant throughout a bout of exercise. The purpose of this study was to investigate the appropriateness of this assumption. Twelve women and eight men volunteered for the study and completed cycle ergometer tests that resulted in exhaustion after ~4 min and ~8 min. In each test, AOD was calculated by subtracting accumulated oxygen uptake (in mL·kg^-1) from estimated total oxygen cost (in mL·kg^-1), which was estimating two ways: (i) assuming that oxygen demand (in mL·kg^-1·min^-1) increases over the course of the exercise bout and (ii) assuming it remains constant. Values for AOD in the 4-min and 8-min tests were expected to be the same (maximal). Mean values for AOD in the 4-min and 8-min tests were similar (79.1 ± 7.6 mL·kg^-1 and 79.6 ± 8.3 mL·kg^-1) when calculated assuming an increase in oxygen demand, but different (71.0 ± 7.9 mL·kg^-1 and 42.5 ± 7.6 mL·kg^-1) when the demand was kept constant. These results support the hypothesis that oxygen demand increases during exhaustive severe intensity cycling exercise. This increase must be included in calculation of AOD.