Without knowing the op’s condition (so take this with a grain of salt), I’d advise against running 5km each & every day as it could wear out your knees, specially running on harder terrain (as most do).
For amateur practitioners it’s good to alternate different activities so that certain muscles get to recover.
Agree but the point was to try a light version of the challenge and you may get the determination to do the full version. Sure, running or any high impact sport can do damage to joints.
Do you have some evidence to back that claim? I run long distances, and whilst I have been given repeated advice of this nature, I have never seen any actual evidence that this is a problem?
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.
For amateur practitioners it’s good to alternate different activities so that certain muscles get to recover.