After a long trail race, some of your red blood cells may not bend the way they should. That matters because red blood cells have a tight job description.

Running extreme distances may strain more than just muscles and joints. New research suggests ultramarathons can alter red ...

Ultramarathons might push red blood cells past their limits—accelerating their aging in the process.

Red blood cells transport oxygen throughout your body, including to vital organs and tissues. They also help your body get rid of carbon dioxide. Too little or too many red blood cells may be ...