GET IT? Because there's a TRACK. There's a running machine with a TRACK and jogging TRACKS often run through places like "mountains" and "country," and since Richie is drawn to those things and this type of activity, the pun is JUSTIFIED.
But that's the legal minimum for a permissable pun.
This was just a prototype machine. The one finally sold by Rich Industries put the scenery in front of the runner, so he didn't stare at the wall while he exercised. Also, the retail version was not scaled for pudgy midgets.
Good thing the "Mountains" button lights up, or you'd never know which option you'd pressed.