Accumulated oxygen deficit on a continuous incremental exercise test

Exercise tolerance is limited by maximal accumulated oxygen deficit (MAOD) for constant work rate exercise tests (CW) in the severe intensity domain ( J Appl Physiol 64: 50–60, 1988). Unpublished data from our laboratory indicate that endurance trained subjects performing a continuous incremental test (CI) reach exhaustion in concert with MAOD. The purpose of the present investigation was to determine whether untrained subjects also achieve MAOD on an exhaustive CI. On a motorized treadmill, eight recreationally active males (VO 2 max 50.9 ± 6.5 mL×kg −1 ×min −1 ) completed: a) sub‐maximal tests (SMT) to establish the grade‐VO 2 relationship at the speed that elicited 4 mM blood [lactate] (S4), b) a CI at S4 to determine VO 2 max and accumulated oxygen deficit (AOD CI ), c) a CW to confirm VO 2 max, and d) a CW that induced exhaustion in 2–4 min to ascertain MAOD. O 2 demand was linearly extrapolated from the VO 2 response at each grade on the SMT. Data were analyzed by repeated measures ANOVA. Each subject manifested blood [lactate] > 8.0 mM and RER > 1.10 on the CI. Peak VO 2 on the CI (3.93 ± 0.56 L×min −1 ) tended (p = 0.054) to be greater than on the CW (3.85 ± 0.53 L×min −1 ). AOD CI (38.1 ± 21.0 mL×kg −1 ) was significantly lower (p < 0.05) than MAOD (50.3 ± 16.6 mL×kg −1 ). This may be due to difficulties in the prediction of O 2 demand or differences in the mechanisms of exhaustion in untrained and endurance trained subjects. Estimation of AOD CI is confounded in some cases by non‐linear VO 2 responses, akin to a slow component, driving the measured VO 2 in excess of O 2 demand in the late stages of the CI.