Justin Timberlake was fit to drop when he started shooting new movie Alpha Dog after joining his castmates on director Nick Cassavetes' gruelling bootcamp.
Ironically, the pop star and his pals were playing druggies and thugs in the new drama but Cassavetes wanted them all to look like buff best friends on film.
And he decided to incorporate a strict workout regime with a bonding experience for stars like Timberlake and EMILE HERSCH.
The singer recalls, "That's where we found a chemistry with all of us. We literally went through what hockey players go through to train. It was hours and hours of weight lifting. It was six days a week.
"On week days we would work out for about three hours from nine to noon. We would all meet at this one place and sometimes we work out down in Venice, California.
"We would run the stairs in Santa Monica, California. We would run the beach. We'd do drills on the beach.
"On Saturday we would box. It was pretty intense training. I've toured since I was 14 years old and I've never done anything as physically taxing as this."