Answer:
Normal athletes have less RBC in comparison to the athletes that are doping and get less oxygen due to less RBC to have less hemoglobin that carries the oxygen so the athlete will get less energy due to normal cellular respiration that will lead to a tired state for muscles.
On other hand, an athlete with doping would have extra RBC which means more hemoglobin to carry the oxygen to the muscles and generate more energy and faster cellular respiration and will get tired comparatively late.
