Exercise hemorheology: Moving from old simplistic paradigms to a more complex picture

Abstract

Classic studies on exercise hemorheology evidenced that blood fluidity is impaired during exercise (short term exercise-induced hyperviscosity) and is improved as a result of regular exercise practice (hemorheologic fitness). Extensive description of these events led to the concepts of "the triphasic effects of exercise", "the paradox of hematocrit", and "the hemorheological paradox of lactate". However, some results obtained in training studies do not fit with this classical picture and cannot be explained by a simplistic paradigm based on the Hagen-Poiseuille law. Taking into account the non-linearity of the effects of viscosity factors on blood flow and oxygen delivery helps to elaborate another picture. For example, moderately high values of hematocrit and erythrocyte rigidity induced by high intensity exercise are likely to trigger a physiological vasodilation improving circulatory adaptation (rather than limiting performance as was previously assumed). This may apply to the acute rise in red cell rigidity observed during strenuous exercise, and also to the paradoxical rise in hematocrit or red cell rigidity observed after some training protocols and that did not fit with the previous (simplistic) paradigms. The "healthy primitive lifestyle" hypothesis assumes that evolution has selected genetic polymorphisms leading to insulin resistance as an adaptative strategy to cope with continuous low intensity physical activity and a special alimentation based on lean meat and wild herbs (i.e., moderately high in protein, rich in low glycemic index carbohydrates, and poor in saturated fat). We propose here that this model may help to explain on an evolutionary perspective these apparently inconsistent findings. The pivotal explanation is that the true physiological picture would be that of an individual whose exercise and nutritional habits are close from this lifestyle, both sedentary subjects and trained athletes representing situations on the edge of this model.

Nanomedicine in Cancer Pathology

“…Rheological properties of blood are highly affected by exercise training. A "triphasic" action of exercise on blood rheology has been proposed [75,76]. It is reported that short-term effect of exercise is an increase in blood viscosity, mostly due to a rise in hematocrit and plasma viscosity induced either by fluid shift, water loss, and release of sequestered RBCs from spleen or water trapping in muscle [76][77][78].…”

“…A "triphasic" action of exercise on blood rheology has been proposed [75,76]. It is reported that short-term effect of exercise is an increase in blood viscosity, mostly due to a rise in hematocrit and plasma viscosity induced either by fluid shift, water loss, and release of sequestered RBCs from spleen or water trapping in muscle [76][77][78]. Likewise, alterations in functional characteristics of erythrocytes have been shown [77,79,80].…”

“…Interestingly, the popular belief that "the more RBCs you have, the fitter you are" seems to disagree with the physiological truth. The important paradox concerning hematocrit in exercise physiology is that "the fitter the athlete -the more fluid is his blood" (hematocrit paradox) [76,84].…”

“…Effects of exercise on hemorheological pattern critically depend on the number of factors, such as: 1) duration of exercise, 2) mode and intensity of exercise training, 3) basal level of physical activity and the training status of the individual, 4) training discipline (please refer to [76,77,85,86] for extensive review). For instance, body builders have been reported to have no improvement in blood rheology after training [80,84] while an increase in viscosity was demonstrated in rugbymen [79].…”

“…A marked increase in blood viscosity is necessary for eNOS-dependent NO production in ECs and, possibly, in RBCs, leading to the adequate vasodilation and beneficial peripheral blood distribution in exercise. This could also explain the hematocrit paradox in athletes -decreased blood viscosity is related to improved aerobic fitness [76,84]. Having decreased resting blood viscosity could be a way to obtain the larger rise in blood viscosity [77] in response to exercise leading to eNOS activation and NO production [76,80,87].…”