Actually I asked my vet the same question about Mister. He was 2.5 just a year ago now he is 4. What they told me to do was up his food intake and do muscle active exercises such as agilty. Running him up stairs things like that. And it does work...Mister didn't get fatter but where muscle weighs more then fat that is where he gained his weight. Hope that helps somewhat.

Oh and Mister says hi to joey