Determinants of VO2 max: insights gained from non-human species

Lars Hermansen's distinguished but prematurely ended career was associated with the measurement and interpretation of the functional capacities of a variety of populations which included elite performers. In assessing human performance, the ability to utilize oxygen has become the single most important parameter to exercise physiologist. Despite the number of experiments that have been conducted on oxygen consumption during the past decades, the responsible mechanisms continue to be debated and investigated. The increasing limitations being placed on human research encourages exercise scientists to use animals to investigate unresolved issues. Surprisingly, there is a dearth of experimental animal studies in which measurements of VO2max, cardiac output (Q) or a-vO2 differences have been made simultaneously. From the data available, it appears that the mongrel dog and the rat exhibit changes in Q, stroke volume and a-vO2 differences that are similar to those reported for humans. On the other hand, foxhounds would appear to be the animal of choice to study VO2max improvements associated with only changes in cardiac output. Because of the role of the spleen as a reservoir for erythrocytes, the horse would be the appropriate animal to investigate changes in VO2max that would be mediated by alterations in the oxygen content of the blood. Interestingly, cattle could be the animal of choice to study the relationships between cardiac contractility, Q, stroke volume and VO2max. Extensive investigations with rats have demonstrated that VO2max can be increased by endurance training in most animal models for disease or hormonal deficiencies. It is apparent from the literature that in the area of VO2max determinations and mechanisms, animal exercise physiologists have not progressed to the degree of sophistication exhibited by human exercise physiologists. However, it is predicted that by the next decade, this situation will no longer exist and human physiologists will utilize various animal models to advance their understanding of the VO2max changes with aging, training, disease or combinations thereof.