MRI Cartilage Assessment of the Subtalar and Midtarsal Joints During a Transcontinental Ultramarathon - New Insights into Human Locomotion A German group has examined with MRI what happens to the joints in the feet when running through Europe.
It showed that the run over almost 4500 km leads to an adaptation of the cartilage. The study can be found under https://pubmed.ncbi.nlm.nih.gov/29190850/