I do some of the exercises you list as physical therapy for my arthritis. One that I do is a sort of half-pushups and half-plank; I place my elbows on the seat of the sofa, then stretch my legs out behind me straight, then do about 30 half-pushups. I finish with the half-plank, holding it for as long as I can. It's about 3 minutes before my shoulders and arms start trembling.