Hollywood actress Jennifer Aniston kept herself fit while shooting for her upcoming film 'The Bounty' by running around horsetracks.

The former 'Friends' star has been running around New Jersey's Monmouth Park horseracing track every day to keep fit while shooting for the movie, as reported.

The 40-year-old actress amazed crew on the set of the new movie, which also stars Gerard Butler, by getting up at 5am and running laps around the racecourse, which is near where she has been shooting on location.

"She showed up every morning at 5am to run laps on the giant oval for a solid hour before cameras rolled. She's really disciplined about keeping fit. She'd get there before everyone else and zip around that huge track like a winner!" said a source.

Aniston's main exercise is running and she prefers it to other fitness routines because it keeps her thighs and calves toned.

This is not the first time details of Jennifer's early morning exercise schedule have been revealed. Earlier this year, it was claimed she was getting up at 3am to ensure she still had time to work out and stick to her hectic shooting schedule for 'The Bounty'.