Effect of exercise intensity on relationship betweenVO2max and cardiac output

Purpose: The purpose of this study was to determine whether the maximal oxygen uptake ((V) over circleO(2max)) is attained with the same central and peripheral factors according to the exercise intensity. Methods: Nine well-trained males performed an incremental exercise test on a cycle ergometer to determine the maximal power associated with (V) over circleO(2max) (p (V) over circleO(2max)) and maximal cardiac output ((Q) over circle (max)). Two days later, they performed two continuous cycling exercises at 100% (tlim100 = 5 min 12 s +/- 2 min 25 s) and at an intermediate work rate between the lactate threshold and p (V) over circleO(2max) = 12 min 6 s 3 min 5 s). Heart rate and stroke volume (SV) were measured (by impedance) continuously during all tests. Cardiac output ((Q) over circle) and arterial-venous O-2 difference (a-vO(2) diff) were calculated using standard equations. Results: Repeated measures ANOVA indicated that: 1) maximal heart rate, (V) over circleE, blood lactate, and (V) under circleO(2) ((V) under circleO(2max)) were not different between the three exercises but (Q) over circle was lower in tlimDelta50 than in the incremental test (24.4 +/- 3.6 L(.)min(-1) vs 28.4 +/- 4.1 L(.)min(-1); P < 0.05) due to a lower SV (143 +/- 27 mL(.)beat(-1) vs 179 +/- 34 mL(.)beat(-1); P < 0.05), and 2) maximal values of a-vO(2) diff were not significantly different between all the exercise protocols but reduced later in tlimDelta50 compared with tlim100 (6 min 58 s +/- 4 min 29 s vs 3 min 6 s +/- 1 min 3 s, P = 0.05). This reduction in a-vO(2) diff was correlated with the arterial oxygen desaturation (SaO(2) = -15.3 +/- 3.9%) in tlimDelta50 (r = -0.74, P = 0.05). Conclusion: (V) over circleO(2max) was not attained with the same central and peripheral factors in exhaustive exercises, and tlimDelta50 did not elicit the maximal (Q) over circle. This might be taken into account if the training aim is to enhance the central factors of (V) over circleO(2max) using exercise intensities eliciting (V) over circleO(2max) but not necessarily (Q) over circle (max).