Ari Weller, the founder of Philosofit, the fitness studio across the street from the Y.M.C.A. East Hampton RECenter, gave a movement and stretching class at one of his client’s houses this past summer, in which, as it turned out, one of the participants was Dr. Mehmet Oz of television fame, who, until he encountered Weller, had thought there was nothing to be done about his chronic knee pain.