Blood oxygen transport regulation by physical activity increase within training dynamics is provided with different mechanisms: from the quantitative and qualitative erythron restructure (including endogenous erythropoietin rise and main erythrocyte index shifts) to change in haemoglobin affinity to oxygen, its heterogeneous structure and blood flow growth as a result of endothelium hyperpolarisation. However, the erythrocyte itself remains a key performer in blood velocity control, due to its structure and functions. This review summarizes the data of modern scientific literature on the characteristics of erythrocytes, which make these cells one of the key links in the oxygen transport system of the blood. The focus on this property of erythrocytes during physical activity is based on the fact that the athlete’s muscles must be supplied with enough oxygen to ensure high performance. Specific training and extra-training factors affecting the content of erythrocytes have been determined. The membrane structure is treated as a significant erythrocyte part in determining its deformation and microvascular blood transport. Enzymes associated with the erythrocyte membrane and affecting cell viability and performance are described. Besides, it is stressed on monitoring erythrocyte indices via modern equipment and assessing lipid peroxidation, which leads to disorders in erythrocyte membrane structure and functions.