Aghast wrote:
The limiting factor is delivery NOT the rate at which the mitochondria can reduce oxygen
http://www.ncbi.nlm.nih.gov/pubmed/10647532
In mostly untrained individuals that is true. Most EPO users don't fit that group. It is true that VO2Max at lower levels is mostly not limited by mitochondrial processes, however long term improvement in VO2Max does tend to come from improvements in this area, rather than O2 delivery/cardiac output.
It seems reasonable to assume that the type of athletes that use EPO have already maxed out the non-peripheral VO2Max mechanisms and are in the area where mitochrondrial processes DO become part of the limitations on further increases.
From the full article:
"there is some evidence that the increase in mitochondria play a permissive role in allowing V ̇O2max to increase. Holloszy and Coyle (44) note that the lowest value for SDH activity in the elite runners studied by Costill (16) was still 2.5-fold greater than that found for untrained individuals in the same study. The increase in muscle mitochondria may allow a slightly greater extraction of O2 from the blood by the working muscles, thus contributing in a minor way to increased V ̇O2max"
In other words in elite athletes who have presumably close to maxed out their Vo2max, mitochrondria are at least somewhat limiting, otherwise increasing their number would not increase Vo2max at all.
And from the wikipedia article on v-o oxygen difference (an indication of the rate at which oxygen is extracted from the blood, i.e. peripheral efficiency):
"Research has shown that following the commencement of exercise there is a delay in the increase of the a-vO2 diff, and that a-vO2 diff only has a marginal impact in the total change in VO2 in the early stages of exercise. The bulk of the early increase in oxygen consumption after a sudden change in exercise levels results from increased cardiac output.[4] However it has also been found that the increase in the maximal a-vO2 diff resulting from adaptations to a physical training program can account for most of the difference in VO2 max in subjects participating in sub-maximal exercise"
So again, as vo2max reaches maximum, it is not cardiac output/oxygen carrying properties of the blood, but the rate of the extraction of that oxygen that becomes most important.
The fact is, that from a scientific research point of view, the verdict is still out on whether elite athletes get significant performance benefits from EPO administration.
However, EPO is highly recommended for sedentary runners with Kidney disease if they want to run a decent 5000m in a few weeks :-)