Non-linear relationships between central cardiovascular variables and VO_2 during incremental cycling exercise in endurance-trained individuals

摘要

Aim. The purpose of this study was to examine the relationships between the central cardiovascular variables (cardiac output, stroke volume and heart rate) and oxygen uptake (VO_2) during continuous, incremental cycle exercise to maximal aerobic capacity (VO_(2max)). Methods. Twenty-one moderately to highly trained males (n=19) and females (n=2) participated in the study. A baseline maximal exercise test was performed to measure VO_(2max). Following the initial VO_(2max) test, cardiac output was measured (CO_2 rebreathing technique) at rest and 3 times during each of 4 exercise trials (2 submaximal tests to 90% VO_(2max) and 2 maximal tests). Stroke volume and arteriovenous O_2 difference were calculated using standard equations. Results. Significant non-linear relationships were found between all central cardiovascular variables and VO_2 (P < 0.01). A plateau in cardiac output at VO_(2max) was identified in 3 subjects. Stroke volume plateaued at an average of 37±12.5% of VO_(2max) in 18 subjects and increased continuously to VO_(2max) in 3 subjects. The arteriovenous O_2 difference progressively increased to VO_(2max) in 17 subjects and revealed a plateau response in 4 subjects. Conclusion. Our data suggest that there is a significant nonlinear relationship between the central cardiovascular variables and VO_2 during incremental exercise to VO_(2max). Furthermore, depending on the person, VO_(2max) may be limited by cardiac output (evidence of cardiac output [Q] plateau) or peripheral factors (continued increase in Q).