Published on: Feb 18, 2026
Extreme endurance running may significantly damage red blood cells, potentially impairing their ability to function effectively, according to a study published in Blood Red Cells & Iron, a journal of the American Society of Hematology. While the long-term consequences remain uncertain, the findings contribute to growing evidence that extreme exercise may sometimes strain, rather than strengthen, overall health.
Previous research has shown that ultramarathon runners often experience red blood cell breakdown during races, sometimes leading to anemia. However, the mechanisms behind this effect were not well understood. The new study reveals that after long-distance races, red blood cells become less flexible reducing their ability to efficiently transport oxygen, nutrients, and waste products. Researchers also created the most detailed molecular map to date showing how endurance racing alters red blood cells.
The study, led by Dr. Travis Nemkov at the University of Colorado Anschutz Medical Campus, analyzed blood samples from 23 runners before and after two demanding races: the 40-kilometer Martigny–Combes à Chamonix race and the 171-kilometer Ultra-Trail du Mont-Blanc. Results showed consistent mechanical and molecular damage to red blood cells following both events.
Mechanical stress likely resulted from repeated pressure changes during prolonged running, while molecular damage appeared linked to inflammation and oxidative stress. Notably, damage was evident even after the 40-kilometer race and became more pronounced in runners completing 171 kilometers. Researchers suggest that longer distances may lead to greater red blood cell loss and accumulated damage.
The team emphasized that it remains unclear how long recovery takes or whether repeated exposure leads to lasting effects. However, the findings may eventually help guide personalized training, nutrition, and recovery strategies for athletes.
Beyond sports science, the research may also inform transfusion medicine. Red blood cells naturally deteriorate during storage and must be discarded after six weeks under U.S. Food and Drug Administration regulations. Understanding how endurance stress accelerates cellular aging could help improve blood preservation techniques.
Although limited by a small sample size and restricted diversity, the study opens the door for further research into protecting red blood cell health both in athletes and in clinical settings.
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