# Personalized Exercise Training Modulates Red Blood Cell Rheology and Morphology in Long COVID

## TL;DR

Personalized exercise training may improve red blood cell function in Long COVID patients, potentially reducing fatigue and microcirculatory issues.

## Contribution

This study demonstrates that individualized exercise can modulate RBC rheology and morphology in Long COVID patients.

## Key findings

- RBC aggregation indices decreased across training phases in Long COVID participants.
- Morphologically abnormal RBCs decreased in participants who completed the full training program.
- Improved RBC deformability correlated with reduced RBC abnormalities in finishers.

## Abstract

Long COVID is associated with persistent fatigue, exercise intolerance, and microcirculatory dysfunction. Altered red blood cell (RBC) rheology, including impaired deformability and increased aggregation, may contribute to these symptoms, yet the effects of exercise interventions remain unclear. This longitudinal pilot study tested whether an individualized, symptom-responsive exercise program improves RBC rheology in Long COVID. A total of 170 (110 f/60 m) participants entered a five-phase training protocol; 15 completed all phases and formed a predefined finisher subgroup. RBC aggregation and deformability, hematological parameters, and coagulation- and iron-related markers were assessed across phases; RBC morphology was additionally analyzed in finishers at baseline and completion. In the total cohort, aggregation indices decreased across training phases, accompanied by prolonged aggregation half-time, while hematological, coagulation, and iron markers remained largely unchanged. The deformability changes were not uniform in the full cohort; however, finishers showed a deformability shift after completion. Importantly, morphologically abnormal RBC decreased in finishers, and these changes correlated with deformability, suggesting that improved rheology is linked to reduced RBC abnormalities. Prospectively, larger controlled studies are needed to confirm these results and to evaluate whether exercise-induced rheological improvements translate into functional and symptomatic benefits.