the gf has two cats. when we started dating, over 4 years ago, her cat Smokey was large, inactive, and was unable to navigate the stairs to the 2nd floor.
over time, and with a diet change (removal of grains), Smokey has lost weight, become more active (i've even seen her run at times), and frequently changes floors. it seems her previous life was not without damage, as she takes stairs slowly and clumsily, as if she has joint pain.
to our great surprise, two nights ago, we came home to find her asleep on the bed -- newly found jumping ability! i haven't seen her actually jump yet, but every night now she finds her way up.