Modeling Oxygen Dynamics under Variable Work Rate

Measurements of oxygen uptake and blood lactate content are central to methods for assessment of physical fitness and endurance capabilities in athletes. Two important parameters extracted from such data of incremental exercise tests are the maximal oxygen uptake and the critical power. A commonly accepted model of the dynamics of oxygen uptake during exercise at constant work rate comprises a constant baseline oxygen uptake, an exponential fast component, and another exponential slow component for heavy and severe work rates. We generalized this model to variable load protocols by differential equations that naturally correspond to the standard model for constant work rate. This provides the means for prediction of oxygen uptake response to variable load profiles including phases of recovery. The model parameters were fitted for individual subjects from a cycle ergometer test. The model predictions were validated by data collected in separate tests. Our findings indicate that oxygen kinetics for variable exercise load can be predicted using the generalized mathematical standard model, however, with an overestimation of the slow component. Such models allow for applications in the field where the constant work rate assumption generally is not valid.