In his article about What determines the maximum O2 uptake in the body?, Øyvind Skattebo, a PhD student at the Norwegian School of Sport Sciences, went all the way with his research. “All the way” meaning taking measurements of blood volume, heart size and function, blood extraction, muscle tissue biopsies, insertion of a catheter in veins and arteries…, graciously performed by willing test subjects. The result of his research is that it is the amount of exercise, obviously in a healthy, balanced way which determines the maximum O2 uptake in the body.
Here is an excerpt from the article:
“Fitness is synonymous with maximum oxygen uptake.
Endurance is the ability to keep going for a long time at relatively high intensity.
Fitness and endurance are not the same thing, but people usually work on both at the same time.
And the most important finding:
You can increase your maximum oxygen uptake without increasing your blood volume. To date, it was believed that this was necessary.
This assumes that the body adapts at the same time by increasing the size of the heart and/or improving the cardiac function, for example, regardless of the increase in blood volume.
If you lose blood suddenly, your body would manage to compensate for this to an extent: 1.5 to 2 dl. But your maximum oxygen uptake is reduced dramatically if you lose more than this.
You can train your muscles to extract oxygen more effectively from the blood, which involves forming more mitochondria (the “powerhouse” of your cells) and tiny blood vessels (capillaries) in your muscles.
How well muscles manage to extract oxygen from the blood is more important than anyone had believed to date. Even so, the pumping capacity of the heart is the most important element in maximum oxygen uptake.”…
You can read the full article with its fascinating pictures of the experiments here: What determines the maximum O2 uptake in the body?