It's a long and hard story but to cut it short I have a 10 year old collie (from good stock - very powerful father - but who has spent the best part of his life chained to his kennel) who has come to ours to retire. He ripped a few lambs open in his prime & was still worked a bit so you don't have to feel too sorry for him but he's not had the best life.
Now he's got a few acres to run about in, a comfy bed (duvet to lie on), a good friend (chocolate lab) to play with and he's getting decent food (worker dry complete with plenty of water - with the odd treat) and he's happy.
He'll have a good retirement and he'll be looked after well but he comes to us with a very weak back end. Seems to be a bit of arthuritis but I'm not sure it's not just lack of muscle development as a result of years having been tied up.
He has spent the last few weeks running about the woods outside all day then coming in for a big bowl of food and he has made good improvements in size and form and also in his coat. He sometimes seems a lot more agile but other times seems stiff.
I'm just wondering if it is possible for a 10 year old dog to pack on muscle to his back end where it has not previously been allowed to develop or are we kidding ourselves here?... probably a trip to the vets in order I know but interested to hear any views.