Very funny episode and we owe it all to Dwight K. Schrute and his ability to exercise. When Michael grows suscious that his new girlfriend Donna (Amy Pietz) is cheating on him, he has Dwight follow her, which leads him to her gym and thus his "exercise" program. Funny funny stuff. The epilogue at the end where he literally takes over the cycling class was a riot.

Also funny was Darryl's prank on Andy, getting him to believe that he would have to enter witness protection because he will become a whistler blower against Sabre for manufacturing faulty printers.

And yes, Donna is cheating on Michael.