A study published in February 2026 in the journal Blood Red Cells & Iron shows that ultramarathons cause specific damage to red blood cells that could affect how well they function. What caught my eye is how this research gives us the most detailed look yet at how these epic races mess with our blood at a cellular level.
The researchers focused on runners in two tough Alpine events: a 40-kilometre race, and the Ultra Trail de Mont Blanc, which is a brutal 171 kilometres. It’s wild to me that even at 40 kilometres, they already saw clear signs of damage to red blood cells.
What Actually Happens to Red Blood Cells
Red blood cells are essential; they ferry oxygen to muscles and organs and haul away waste. To do their job, they have to stay bendy enough to squeeze through tiny blood vessels all over the body.
For this study, blood samples were taken from 23 runners both before and after their races. The team dug into thousands of components: proteins, lipids, metabolites, trace elements, you name it. What they found was that red blood cells showed damage from two main sources: mechanical stress and molecular changes.
The mechanical damage probably comes from the pounding of running itself. As blood moves faster and harder during intense exercise, the cells get knocked around by shifting fluid pressure. Imagine the cells getting jostled as your heart pumps like mad.
The molecular changes seem to be tied to inflammation and oxidative stress. Oxidative stress pops up when our bodies run low on antioxidants, which normally mop up harmful molecules. During extreme endurance events, this balance gets thrown off.
The Distance Factor
What really stood out to me was how the damage increased with race distance. The signs of damage that speed up ageing and breakdown of red blood cells showed up after just 40 kilometres. But for those who ran the 171-kilometre race, the damage was much more intense.
Travis Nemkov, who led the study at the University of Colorado Anschutz, pointed out that somewhere between marathon and ultramarathon distances, the damage really starts to ramp up. As the race gets longer, athletes lose more blood cells and the ones left take more of a beating.
Damaged red blood cells lose flexibility, which could make it harder for them to carry oxygen, nutrients, and waste efficiently. If you’re pushing your body to the limit, that’s not great news.
The Unknowns
This research gives us a glimpse of what happens during and right after these races, but there are still some big question marks. I keep wondering: how long does it actually take for our bodies to fix this damage? Could any of it be permanent, or maybe even positive in the long run?
The study only checked blood samples right before and after the races. To really get the full picture, we need studies that track athletes for weeks, months, maybe even years after these events.
Broader Implications for Sports Science
The inflammation and oxidative stress during extreme endurance running aren’t just a red blood cell problem. These processes can send ripples through the whole body. Still, this research gives us the most detailed look so far at how red blood cells respond to this kind of stress.
Figuring out these mechanisms could eventually help us come up with ways to boost performance or reduce the downsides. Maybe that means tailored training, special nutrition plans, or smarter recovery tactics. Who knows?
Connections to Blood Storage
Another thing I found interesting: the same patterns of damage seen in ultramarathon runners show up in stored blood for transfusions. Stored blood starts breaking down after a few weeks, and it’s usually not used after six weeks.
The research team pointed out that red blood cells are pretty tough under normal conditions, but they’re surprisingly sensitive to mechanical and oxidative stress. By seeing how extreme endurance pushes these cells toward faster ageing, maybe we can figure out how to better protect blood for both athletes and people needing transfusions.
Study Limitations
It’s worth mentioning that this study only had 23 participants and wasn’t very diverse. So, yeah, we need bigger and more varied studies to really nail down these findings. The research team is planning to include more people and to collect blood samples during the recovery period next time.
