determination of key parameters of oxidative function, namely the maximum O2 uptake (VO2max), VO2 kinetics and work efficiency, provides invaluable information regarding the O2 transport system and integrated cerebral-pulmonary-cardiovascular-muscular function in health and disease. For instance, these parameters relate mechanistically to lifespan, health span, physical exercise performance and exercise (in)tolerance. Moreover, in patient populations, these parameters can stratify individuals for heart transplant procedures, assess surgical outcomes and present sensitive measures of treatment toxicity (e.g., doxorubicin and anthracyclines in cancer) as well as discriminate therapeutic benefits of imposed countermeasures to disease or age-related debilitation. The ramp-incremental exercise test, with gas exchange measurements, was originally devised to provide information on each of these parameters in a single laboratory visit (Whipp et al., 1981). Indeed, this approach forms the basis of clinical cardiopulmonary exercise testing guidelines worldwide (e.g., Palange et al., 2018). However, over time, it became apparent that VO2 kinetics and work efficiency varied considerably with exercise intensity (e.g., Özyener et al., 2001; Rossiter, 2011), and therefore new approaches were needed to evaluate these diverse aspects of oxidative function in a single exercise test.
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