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

Area of Science:

• Exercise physiology
• Hemodynamics
• Evolutionary biology

Background:

• Classic exercise hemorheology describes impaired blood fluidity during exercise (exercise-induced hyperviscosity) and improvement with regular training (hemorheologic fitness).
• Established concepts include "triphasic effects of exercise," "paradox of hematocrit," and "hemorheological paradox of lactate."
• Some training study results challenge simplistic models based on the Hagen-Poiseuille law.

Purpose of the Study:

• To re-evaluate exercise hemorheology by considering non-linear effects on blood flow and oxygen delivery.
• To explain seemingly inconsistent findings in training studies using an evolutionary perspective.
• To propose the "healthy primitive lifestyle" hypothesis as a unifying model.

Main Methods:

• Review and synthesis of existing literature on exercise hemorheology and training adaptations.
• Analysis of non-linear relationships between viscosity factors, exercise intensity, and circulatory responses.
• Application of the "healthy primitive lifestyle" hypothesis to interpret observed hemorheological phenomena.

Main Results:

• High hematocrit and erythrocyte rigidity during intense exercise may induce physiological vasodilation, aiding circulatory adaptation.
• Acute increases in red cell rigidity during strenuous exercise and paradoxical increases post-training are better explained by non-linear models.
• The "healthy primitive lifestyle" model suggests genetic adaptations for insulin resistance, optimizing responses to low-intensity activity and specific diets.

Conclusions:

• A nuanced understanding of exercise hemorheology requires acknowledging non-linear physiological responses.
• The "healthy primitive lifestyle" provides an evolutionary framework to explain complex and sometimes paradoxical hemorheological adaptations in both athletes and sedentary individuals.
• Individuals whose habits align with this ancestral model may represent a physiological optimum, with sedentary and highly trained states existing at the edges.