i don't know if it's *twice* but it's still a significant amount more. i think a lot depends on you and on the individual dogs involved. a big part of the reason why i got mushroom was so that luce'd have a playmate to help her get enough exercise. HA! they'll play biteyface in the house, but exercise each other outside?? you've got to be kidding! they totally ignore each other outside unless i instigate games of tug or something between them. so as far as exercising, yes, it is twice as much work with my two. and also, if you end up with multiple dogs with health issues at the same time, it can be really expensive and tremendously stressful.