The Fick equation holds that oxygen uptake (Vo(2)) is the product of cardiac output and arterial venous oxygen difference. Factors limiting Vo(2) (ie, maximal Vo(2)) with exercise have therefore been traditionally sought within the determinants of cardiac function. However, such an approach ignores a large body of research evidence indicating that peripheral factors, particularly arteriolar dilatation and skeletal muscle pump function, control circulatory responses to exercise rather than central cardiac mechanisms. Efforts to understand the limiting factors for physiologic aerobic fitness are thus more appropriately directed toward characterizing these peripheral determinants of blood flow.