Accumulated oxygen deficit on a continuous incremental exercise test

Abstract

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 Unpublished data from our laboratory indicate that endurance trained subjects performing a continuous incremental test (CI) reach exhaustion in concert with MAOD.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 (VO2max 50.9 ± 6.5 mL×kg−1×min−1) completed: a) sub-maximal tests (SMT) to establish the grade-VO2 relationship at the speed that elicited 4 mM blood [lactate] (S4), b) a CI at S4 to determine VO2max and accumulated oxygen deficit (AODCI), c) a CW to confirm VO2max, and d) a CW that induced exhaustion in 2–4 min to ascertain MAOD. O2 demand was linearly extrapolated from the VO2 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 VO2 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). AODCI (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 O2 demand or differences in the mechanisms of exhaustion in untrained and endurance trained subjects. Estimation of AODCI is confounded in some cases by non-linear VO2 responses, akin to a slow component, driving the measured VO2 in excess of O2 demand in the late stages of the CI.