Could plasma protein levels be a surrogate for VO2 max testing as a measure of cardiorespiratory fitness?

The evidence that increasing cardiorespiratory fitness (CRF) levels positively correlates with improved mortality and morbidity is indisputable. The most accurate way of assessing CRF is by measuring the ventilation rate of oxygen during a maximal exercise test, also known as a VO2 max test. Yet maximal exercise tests have significant overhead, which makes them infeasible to perform regularly on all patients.¹ Most people will have to seek out (and pay out-of-pocket for) a VO2 max test unless there is a clinical…