Influence of age and gender on cardiac output-VO2 relationships during submaximal cycle ergometry

It is presently unclear how gender, aging, and physical activity status interact to determine the magnitude of the rise in cardiac output (Qc) during dynamic exercise. To clarify this issue, the present study examined the Qc-O2 uptake (Vo2) relationship during graded leg cycle ergometry in 30 chronically endurance-trained subjects from four groups (n = 6-8/group): younger men (20-30 yr), older men (56-72 yr), younger women (24-31 yr), and older women (51-72 yr). Qc (acetylene rebreathing), stroke volume (Qc/heart rate), and whole body Vo2 were measured at rest and during submaximal exercise intensities (40, 70, and approximately 90% of peak Vo2). Baseline resting levels of Qc were 0.6-1.2 l/min less in the older groups. However, the slopes of the Qc-Vo2 relationship across submaximal levels of cycling were similar among all four groups (5.4-5.9 l/l). The absolute Qc associated with a given Vo2 (1.0-2.0 l/min) was also similar among groups. Resting and exercise stroke volumes (ml/beat) were lower in women than in men but did not differ among age groups. However, older men and women showed a reduced ability, relative to their younger counterparts, to maintain stroke volume at exercise intensities above 70% of peak Vo2. This latter effect was most prominent in the oldest women. These findings suggest that neither age nor gender has a significant impact on the Qc-Vo2 relationships during submaximal cycle ergometry among chronically endurance-trained individuals.