Secret behind Swank`s svelte frame

London: At 37, actress Hilary Swank can easily flaunt a bikini, and she has her fitness regime to thank for it.

The actress was pictured on the Hawaiian island of Kauai wearing a skimpy black two-piece with her long-time agent and boyfriend John Campisi, reported.

When the Los Angeles-based girl is not on a holiday, Swank works hard at maintaining her figure with rigorous workout sessions. She wakes up at the crack of dawn most days and heads to Santa Monica for an hour-long workout.

She often meets her personal trainer for a gruelling session, including a mix of boxing and sparring and free weights.

"She is also a big fan of the spin class," a fellow gym-goer said.

"Hilary just looks incredible. She is tiny and so toned. Everyone looks at her with these envious eyes, but when it comes to her exercise she is not the one to hold back. She goes for it full throttle," said the source.