# Rheological and Biochemical Properties of Blood in Rumers: A Preliminary Report
## 4 Discussion
The three suggested conclusions were as follows: (1) in athletes, beneficial blood rheological properties may enhance blood flow in working muscles, increasing work output; (2) the received outcomes support the concept of a link between blood rheological properties and arteriogenesis; (3) regular physical activity may increase blood flow in patients with ischaemic vascular diseases. According to [PERSON] et al. [6], moderately high haematocrit and erythrocyte stiffness values induced by high-intensity exercise are likely to induce physiological vasodilation, thus improving cardiovascular adaptation. As observed by [PERSON] et al. [15], a 10,000 m run had no effect on the athletes' blood rheological properties, which corroborates the findings of our study. [PERSON] et al. [16, 17] state that the mechanism causing disturbances in erythrocyte deformability during prolonged physical effort with high oxygen consumption consists of oxidative stress resulting from the production of free oxygen radicals, originating in the mitochondria, leukocytes, or temporary tissue hypoxia. It has been reported that during exercise, an increase in erythrocyte stiffness is observed, followed by a gradual return to baseline. Another cause of impaired deformability is a rise in lactate concentration above 4 mmol/L as a product of anaerobic glycolysis. Such a trend was noticed in the present study. Nevertheless, the erythrocytes of a trained individual are adapted to cope with lactate (and oxidative stress), which manifests as no reduction in deformability during exercise [18]. In turn, [PERSON] et al. [19] determined blood parameters in competitive runners covering a distance of 10 km. The mean corpuscular volume increased, and haemoglobin concentration, as reflected by the mean corpuscular haemoglobin concentration indicator, decreased after exercise, which may suggest poor blood cell hydration. The deformability of red blood cells increased, and the level of red blood cell aggregation and plasma viscosity decreased, while haematocrit remained unchanged. The effort did not affect cryptosis markers, and the 10 km run did not have an impact on blood cell ageing. The increased deformability of red blood cells occurred, according to the researchers, as a result of rehydration, which led to a decrease in blood viscosity. In a study involving endurance athletes, [PERSON] et al. [20] reported a difference between cycling and running effort. A cycle ergometer test resulted in a rise in blood viscosity and red blood cell aggregation and had no significant effect on red blood cell deformability. During the run, blood viscosity did not change, but red blood cell deformability increased. This dissimilarity in the rheological properties of red blood cells while running and cycling may be due to a decrease in the arterial partial pressure of oxygen (hypoxaemia) during running. [PERSON] et al. [21] observed different rheological properties of blood in runners taking part in shorter- and longer-distance mountain runs. Red blood cell deformability at high shear forces and haematocrit decreased after a long-distance ultramarathon (171 km), but did not change after a 40 km run. Haemoglobin concentration and haemolysis rate remained unchanged over both distances. Erythrocyte aggregation and blood viscosity only increased for the shorter run. Lower blood viscosity in mountain ultramarathon runners facilitates blood flow to the muscles. In a study involving runners who participated in a 24 h ultramarathon, [PERSON] et al. [22] reported decreased concentrations of erythrocytes, haemoglobin, haematocrit, mean corpuscular haemoglobin, free haemoglobin, and iron (unsaturated iron-binding capacity) after the race completion. Reticulocyte and ferritin concentrations were significantly higher after the effort. Of the 19 runners, 15 exhibited changes in the elasticity and viscosity of red blood cells, which were associated with altered concentrations of red blood cells, as well as haemoglobin and haematocrit.