Kristen Stewart and Garrett Hedlund powered through their threesome scene in On the Road.

The pair star in the independent drama based on beat generation author Jack Kerouac's classic novel. The semi-autobiographical story follows Sal Paradise, portrayed by Sam Riley, on a journey across America with his best friend Dean and his friend's wife Marylou.

Kristen and Garrett reveal that they got a little loony while shooting the graphic sex scene with co-star Sam Riley.

"You just do it, there's no other way," Garrett told Extra in a joint interview with Kristen on the red carpet of On The Road's Toronto International Film Festival Thursday.

"I like to push myself... you couldn't do this job in any genuine sense unless you so completely believed in it, almost like a psychopath," Kristen explained.

"Are you saying you're crazy?" Garrett inquired.

Kristen replied, "Yeah, just a little bit, probably just a little bit."

Kristen was excited to greet her fans at the premier, which marks her first public appearance since she apologised for cheating on Robert Pattinson with director Rupert Sanders.

She appreciated the love she received from the crowd.

"It means everything [to have the support of the fans]," she said.

"My answer would be no different if I was here for a Twilight movie, which I think says everything. I love this movie. I'm so proud of this movie and I'm so proud of everyone I'm here with."