And it could go a long way to explaining how Biel could transition from 30-year-old Justin Timberlake to her much older co-star.
As he splashed around in Maui 300 star Butler, who played King Leonidas in the epic, looked to have maintained the Spartan work-out from the film four years ago.
To play the warrior, he undertook gruelling training for eight months at the hands of former mountain climber, Mark Twight.
He admitted it was hard to abandon the regime after the film was shot, admitting that he revelled in feeling ‘like a lion.’
This attitude certainly can’t fail to impress Biel, whatever the state of their relationship is at present.
Thepair, who are soon to be be seen together in new film Playing the Field, have denied a love affair, claiming to be just good friends.
Rumours of a burgeoning love affair first surfaced in March when they twosome were filming scenes for the movie in Louisiana.
Sourceson the set quashed suggestions of romance, however, claiming that the pair had never even enjoyed a private dinner together.
But pictures of Biel riding behind Butler on his Harley Davidson last week suggest that the actors are very cosy indeed.
Biel could be seen clinging to the Scotsman as they sped along the Pacific Coast Highway in LA.
After a long-term relationship with the flirty Timberlake, Biel might want to be wary of dating ladies man Butler.
He has a history of dating leading women, most notably Butler was linked to Jennifer Aniston, 42, when theyfilmed The Bounty Hunter.
Itwas also reported that he tried to chat up actress Kirsten Dunst, 29 , at a party during the Cannes Film Festival, where he was promoting Coriolanus, an adaptation of the Shakespeare play directed by Ralph Fiennes.
Butler even sends up his reputation in Playing the Field.
In it he stars as a professional athlete with a weak past who tries to redeem himself by coaching his son’s soccer team.
But he find himself unable to resist his players’ restless and gorgeous mothers.
Gerard has also just completed filming on two films to be releases this year, Machine Gun Preacher and Movie 43.
Theformer is the true story of Sam Childers,a former drug-dealing biker who became a crusader for hundreds of Sudanese children who’ve been forced to become soldiers.
Movie43 is an ensemble comedy of short stories starring a host of big names including Hugh Jackman, Kate Winslet, Anna Faris, Kristen Bell, Emma Stone, Jush Duhamel and Richard Gere.
Naomi Watts, Sean William Scott, Elizabeth Banks and Uma Thurman also star.
Hewill also reprise his role in the animated children’s film How to TrainYour Dragon, which is nominated for best animated feature at this month’ Academy Awards.