Maximal oxygen uptake the previous section we considered how Q limiting step in the transport of O2 to exercising In this section the ability of the body to take external work will be discussed In the previous section the analogy of a haulage supplying goods to stores was used to illustrate role of Qin oz transport. In an extension to that e can think of O2 uptake (VO2) by the muscles to the sales of the goods, which are a the of delivery and the customer demand; required in order to achieve sales. In the same voz is a function of blood flow and O2utilization. lization of O, is the amount of O2 extracted from as it passes through the tissue, i e., the arterial venous O2 difference (a-vO2). Thus, the voa is given by the equation: During exercise, not only does blood flow to a muscle il- ur increase, but the extraction of oxygen from the blood is also he enhanced, widening the a-vO2. The vo2 of the entire body can be measured by using the a-vO2 difference measured at the lungs. Typically, this gra- n- dient is around 5 ml at rest, but can be three times this me value during heavy exercise. The change is generated by ed an increased extraction of O2 by the muscles, which pro- duces a reduction in mixed venous O2 content and a wider ne a-vO2 difference. However, measuring Q and pulmonary of a-v O2 difference is a highly invasive method of assessing en total body VO2; fortunately, it can also be estimated by O2 subtracting the amount of oxygen exhaled from the en amount inhaled at the mouth The maximal oxygen uptake 2maxy also called maximal (VO a- oxygen consumption or aerobic capacity) is an index that at combines both the maximal ability to transport and to utilize