Oxygen Uptake-Work Rate Relationship During Two Consecutive Ramp Exercise Tests

The performance of prior high intensity constant work rate (CWR) exercise significantly influences the gain of the fundamental oxygen uptake (VO2) response during subsequent high intensity CWR exercise. The purpose of the present study was to investigate whether equivalent effects could be elicited in the second of two bouts of exhaustive ramp exercise. We therefore hypothesised that a prior bout of exhaustive ramp exercise would increase the VO2-work rate (DeltaVO2/DeltaWR) slope during subsequent ramp exercise. Nine healthy males performed two ramp exercise tests to exhaustion on an electrically braked cycle ergometer separated by a 10-min period of cycling at 20 W. Pulmonary VO2 was measured breath-by-breath throughout both tests, and the mean response time (MRT) and the DeltaVO2/DeltaWR slope for exercise below the gas exchange threshold (GET) (S1), above the GET (S2), and over the S1 + S2 region (ST) were determined. Paired t-tests were used to analyse the data with significance accepted at p < 0.05. Blood [lactate] was higher at the onset of the second ramp test compared to the first (mean +/- SEM 1.2 +/- 0.1 vs. 6.2 +/- 0.7 mM; p < 0.01), but baseline VO2 was not significantly different between tests (0.93 +/- 0.05 vs. 0.99 +/- 0.06 L. min (-1)). The MRT (42 +/- 4 vs. 40 +/- 5 s) did not differ between tests, but the DeltaVO2/DeltaWR slope was steeper in the second ramp test for S2 (9.1 +/- 0.4 vs. 9.8 +/- 0.5 ml. min (-1). W (-1); p < 0.01) and ST (9.0 +/- 0.4 vs. 9.6 +/- 0.5 ml. min (-1). W (-1); p < 0.05). The demonstration that prior ramp exercise increases the DeltaVO2/DeltaWR slope during subsequent ramp exercise is consistent with the results of previous CWR studies and indicates that exercise economy is sensitive to the prior activity of the engaged muscles.