https://acrabstracts.org/abstract/prevalence-of-knee-pain-in-ultramarathon-runners/ https://acrabstracts.org/abstract/prevalence-of-knee-pain-in... - evidence o

https://acrabstracts.org/abstract/prevalence-of-knee-pain-in-ultramarathon-runners/ https://acrabstracts.org/abstract/prevalence-of-knee-pain-in... - evidence of reduced risk. However the thing is the group is self selecting, people who experience joint problems stop running or do not run ultramarathons. (Ex-runners in this study did not in general stop because of joint problems.) Ultimately, the activity seems safe from standpoint of miles ran.