My mixed breed medium size dog is very energetic. I walk him and his same sized female sidekick faithfully each day.  She is relaxed most of the time, but he still has a great deal of energy.  I'm using the chuckit to give him more active playtime and it seems to be working very well.  I walked him after a chuckit session and he was very well behaved, not pulling on the leash as much as he usually does.