Ultra-Marathon Running May Impact Red Blood Cell Flexibility, Study Shows
A recent study has revealed that pushing the body to extreme distances, such as in ultra-marathons, can have negative effects on red blood cells. These cells, responsible for delivering oxygen and removing waste throughout the body, may become less flexible under the stress of prolonged endurance activities.
While the research did not delve into the long-term health implications of this phenomenon, earlier studies have suggested that reaching biological limits in this way could potentially be harmful. The international team of researchers behind the study theorizes that the strain of ultra-endurance running exceeds the body’s natural recovery capabilities, leading to damage to red blood cells.
Red blood cells are particularly vulnerable to this stress as they lack a nucleus and cannot repair themselves by producing new proteins. However, the researchers have refrained from advising against participating in ultra-marathon events, stating that more research is needed to fully understand the implications.
Dr. Travis Nemkov, a biochemist and molecular geneticist from the University of Colorado Anschutz (CU Anschutz), explains, “When individuals engage in these types of events, persistent stress can damage the most abundant cell in the body.”

The study involved 23 elite runners participating in races of varying distances, with blood samples collected before and after the events. The analysis revealed that red blood cells exhibited signs of damage from both physical strain and internal chemical changes, with more pronounced damage observed in runners covering longer distances.
Notably, red blood cells in ultra-marathon runners showed increased stiffness, potentially impeding their ability to circulate effectively in the body. Additionally, a key red blood cell repair mechanism known as the Lands cycle was found to be overwhelmed in runners completing longer distances.
Dr. Nemkov highlights the impact of this damage, stating, “Between marathon and ultra-marathon distances, the damage becomes more apparent. However, the long-term effects and implications of this damage remain unknown.”
While the study provides valuable insights, it is essential to consider its limitations, such as the small sample size and the variability in race conditions. Further research is needed to explore these findings in larger cohorts over extended periods.
Interestingly, the study also draws parallels between the damage observed in ultra-marathon runners and the lesions seen in stored blood for transfusions. This connection suggests that extreme endurance events could offer insights into enhancing blood storage practices for medical purposes.
Dr. Angelo D’Alessandro, a biochemist and molecular biologist at CU Anschutz, emphasizes the potential for cross-disciplinary learning, stating, “Understanding these shared pathways presents an opportunity to improve blood cell function in athletes and transfusion medicine.”
The research findings have been published in the journal Blood Red Cells & Iron, shedding light on the intricate relationship between extreme endurance activities and red blood cell health.

