GJAC .. I am 65. When I was in my late 30's , I was very active in martial arts, and as such DID .. and still do .. many exercises like you mention, along with sitting with my feet together ( Indian style ) and touching my head to the floor, and holding it there... UNFORTUNATELY ... these never did anything for my knee , but did help in back pain relief.
The stretching I mentioned above DOES !
As for the Arthritis question ... I have no idea.
Several of the Doctors that I have been to, say YES ... Almost all of the reports I read claim the symptoms ARE arthritis ... Yet, the stretching was my own creation, and not to be found ( so far ) anywhere as a remedy to anything to do with Arthritis.
I have heat pads .. several types of massagers & vibrators ... Creams .. magic potions & sprays ...and more ... none of which gave more than temporary relief.
While the future is always uncertain with aches & pains ... I am convinced that my stretch has cured a big problem, and I am thrilled to have stumbled on it.
I hope it becomes an answer to YOU and others as well.
Good Luck ... and happy RV'ing................ Richard