The foot in multistage ultra-marathon runners: experience in a cohort study of 22 participants of the Trans Europe Footrace Project with mobile MRI. Radiologists have examined with a mobile MRI the feet of runners at the 2009 trans-Europa run over 4,487 km. The diameter of the Achilles tendon increased significantly.Also, there was a detectable edema of the feet.
Surprisingly non-finishers developed a more pronounced edema of feet as finishers. All details can be read below https://pubmed.ncbi.nlm.nih.gov/22619270/