Answer:
Red blood cells
Step-by-step explanation:
Red blood cells are the type of cells that is responsible for carrying oxygen to the cells from lungs and dispose off carbondioxide gas from cells to the lungs. At higher altitudes, the oxygen is present in low concentration so for that purpose more red blood cells are required in order to helps in the delivery of oxygen to the muscles because the athletes needs more oxygen so for fulfill the need for oxygen red blood cells are increases.