Attenuated relationship between cardiac output and oxygen uptake during high-intensity exercise

Aim: Recent findings have challenged the belief that the cardiac output (CO) and oxygen consumption (VO2) relationship is linear from rest to maximal exercise. The purpose of this study was to determine the CO and stroke volume (SV) response to a range of exercise intensities, 40100% of VO2max, during cycling. Methods: Ten well-trained cyclists performed a series of discontinuous exercise bouts to determine the CO and SV vs. VO2 responses. Results: The rate of increase in CO, relative to VO2, during exercise from 40 to 70% of VO2max was 4.4 +/- 1.4 L L) 1. During exercise at 70-100% of VO2max, the rate of increase in CO was reduced to 2.1 +/- 0.9 L L) 1 ( P = 0.01). Stroke volume during exercise at 80-100% of VO2max was reduced by 7% when compared to exercise at 50-70% of VO2max ( 134 +/- 5 vs. 143 +/- 5 mL per beat, P = 0.02). Whole body arterial-venous O2 difference increased significantly as intensity increased. Conclusion: The observation that the rate of increase in CO is reduced as exercise intensity increases suggests that cardiovascular performance displays signs of compromised function before maximal VO2 is reached.