Why would injecting more red blood cells into their bodies create an advantage for athletes?

It would be a advantage because red blood cells would carry oxygen and like alot I mean, and the athletes won't run out of breath :3

Explanation:

:3

Considering that it is the correct version of the red blood cell (i.e. it is the type they currently have), having more red blood cells can be advantages for athletes. Oxygen plays an important role in exercising. The more oxygen a person has, the harder they can push onward. In this case, as red blood cells carry oxygen and carbon dioxide, more oxygen can be brought to the muscles and other parts of the body, while carbon dioxide can be removed at a much higher and faster rate, allowing for the athletes to continue forward. Just think of it this way, the more oxygen you have, the more you can do.

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not sure if this is what you'r looking for eubacteria and archaebacteria