I've got the 2 legged jumper for both of mine. They are 7 & 1 and active with no sign of rheumatism or arthritis, but if I still had my older girls I would have got them the 4 legged if only to keep their hips warm. They can put in a waterproof back zip in the 4 legged version if the dog is stiff or arthritic,extra £9