Exercise-induced redox modulation of red blood cell function in health and disease: Mechanistic implications for hemoglobin cycling and microvascular regulation.

Exercise generates transient systemic redox and hemodynamic signals that influence oxygen delivery, vascular tone, and metabolic adaptation in both health and disease. Red blood cells (RBCs) are increasingly recognized as regulated redox-responsive cells rather than passive oxygen carriers. This narrative review integrates mechanistic and translational evidence linking RBC deformability, microvascular transit, and perfusion matching to exercise-induced reactive oxygen and nitrogen species (RONS), hemodynamic shear, hemoglobin redox cycling, antioxidant buffering, and nitric oxide (NO)-related signaling. RBC redox architecture, supported by glutathione and thioredoxin systems maintained by pentose phosphate pathway-derived nicotinamide adenine dinucleotide phosphate (NADPH), limits membrane lipid and protein damage during recurrent oxidative oscillations and restrains hemoglobin auto-oxidation. Exercise-induced changes in red blood cell nitric oxide synthase (RBC-NOS) activity, S-nitrosylation chemistry, nitrite reduction, and adenosine triphosphate (ATP)-mediated purinergic signaling may further influence NO bioavailability and downstream endothelial responses. However, severe, prolonged, unaccustomed, or insufficiently recovered oxidative stress may shift these adaptive responses toward methemoglobin accumulation, band-3 aggregation, vesiculation, phosphatidylserine-positive erythrocyte clearance, hemolysis, and impaired microvascular regulation. We therefore propose an intensity-duration-recovery framework in which moderate, transient, and adequately recovered redox/shear pulses support RBC deformability and microvascular adaptation, whereas prolonged or repeatedly performed high-intensity exercise may exceed erythrocyte buffering capacity and promote hemolytic injury or premature erythrocyte clearance. Because RBC redox dysfunction overlaps with cardiometabolic, vascular, hematological, and exercise-intolerance-related disease settings, standardized RBC-contained redox biomarkers may help improve the interpretation of exercise responses and support phenotype-aware exercise prescription.