Footstrike is the major cause of hemolysis during running.

@article{Telford2003FootstrikeIT,
  title={Footstrike is the major cause of hemolysis during running.},
  author={Richard D. Telford and G. Jr. Sly and Allan G. Hahn and Ross B. Cunningham and C Bryant and J. A. Smith},
  journal={Journal of applied physiology},
  year={2003},
  volume={94 1},
  pages={
          38-42
        }
}
There is a wide body of literature reporting red cell hemolysis as occurring after various forms of exercise. Whereas the trauma associated with footstrike is thought to be the major cause of hemolysis after running, its significance compared with hemolysis that results from other circulatory stresses on the red blood cell has not been thoroughly addressed. To investigate the significance of footstrike, we measured the degree of hemolysis after 1 h of running. To control for the potential… 
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