The primary function of red blood cells is to transport oxygen from the lungs to body tissues and return carbon dioxide to be exhaled. In relation to physical fitness, a healthy number and function of red blood cells enhance aerobic capacity and endurance. Adequate oxygen delivery is essential for efficient energy production during exercise. Individuals engaged in regular physical activities, especially endurance sports, may have higher levels of red blood cells due to increased demand for oxygen. Maintaining optimal levels contributes to improved stamina and overall fitness performance.