Jason Segel and Leslie Mann on the Set of Judd Apatow Movie

Jason Segel and Leslie Mann were hard at work filming scenes for the new Judd Apatow movie yesterday in LA. The costars didn't exactly keep straight faces, as Jason, who plays a personal trainer, coached Leslie through a few ridiculous ab workouts. The film, which was briefly titled This Is Forty, also stars Megan Fox and Bridesmaids actress Melissa McCarthy. The picture revisits the characters that Leslie and Paul Rudd initially played in Knocked Up. Jason Segel has talked about losing weight recently, and took the opportunity to flex his newly revealed biceps in front of Leslie on the set. Jason, who has a cameo in Friends With Benefits, is back to work with the Apatow gang again after shooting The Five Year Engagement in Michigan with costars including Emily Blunt and Mindy Kaling.