Using a randomfile in folder?

Right now my Script looks like that:

ffmpeg -re -stream_loop -1 -i videos/fitness"$(( RANDOM % 8 ))".mp4

It searches for all videos in my folder that starts with "fitness".

fitness1.mp4

fitness2.mp4

fitness3.mp4

and so on...

and it takes 1 randomly between 1-8 ( im using /fitness"$(( RANDOM % 8 ))".mp4 )

Is there a way to just use a random mp4 file from the folder, no matter whats the name is?