Those of us who ride are already convinced of the physical benefits of horseback riding. So while it's pouring rain and cold outside is there a substitute for a good gallop indoors? (No, not the mechanical horse at the grocery store.) The makers of Joba, an exercise machine made to mimic the movements of a horse think so. But writer John Briley of the Washington post is less convinced. And judging from the pictures of Joba the grocery store horse is cuter. These machines are turning up in gyms, so if you can't saddle up and head out on trail, maybe you can head for the local gym.