Anaerobic threshold and the oxygen consumption–cardiac output relationship during exercise

Abstract

There is some evidence that, above anaerobic threshold (AT), the arteriovenous oxygen difference may increase due to a reduced hemoglobin affinity for oxygen. Thus, it should be expected that above AT, the oxygen consumption to cardiac output (VO₂/CO) relationship would become steeper compared to below AT since, if a larger amount of O₂ could be extracted from blood, a lower CO would be required for carrying the same O₂ quantity. We tested the possibility that the VO₂/CO relationship shows a break point after AT, becoming steeper. Cardiodynamics and expired gases were measured with an impedance cardiograph and a mass spectrometer in ten healthy male subjects during an incremental test on a cycle ergometer. We performed three linear regressions for each subject’s VO₂/CO ratio: one for the entire exercise dataset, one for data below AT, and one for data above AT. Statistical comparisons of linear regressions obtained from VO₂ and CO for below and above AT data failed to find any significant difference between these data. This study demonstrates that the slope of the VO₂/CO relationship does not exhibit a break point at AT. Therefore, it seems that AT does not play a key role in affecting this relationship during incremental exercise.