I have a 5 yo TWH gelding who is very lanky and on the thin side, especially his back end. Are there any exercises I can do to help him strengthen the muscles and get him in better gaiting shape? He's pretty pacey right now, but I think that's because he's a little out of shape. Unfortunately, I live in a very flat area with no hills so I can't do hill work. Any suggestions would be great! Thanks!