But would Mr Clayton have run the marathon anywhere near as fast with a much lower absolute oxygen uptake? Of course not. Each individual should aim to push his/her oxygen uptake level as high as possible because it is this that'll determine your performance. Look at the drug Erythropoietin that is currently abused in endurance sports. It raises the oxygen uptake level beyond what can be achieved naturally making athletes much faster than they otherwise have been. If getting oxygen to the cells wasn't the single most important factor in speed over distance this drug wouldn't be such a big problem for the sports authorities.