Sienna undergoes boxing lessons for GI Joe

London (ANI): It seems that Sienna Miller's taxing schedule on the set of her latest film, GI Joe is taking its toll on her. According to friends, the actress is "exhausted" by the physical demands of the military action-thriller. The British beauty, who has been filming in the Czech Republic along with co-stars Christopher Eccleston and Dennis Quaid, has had to undergo boxing lessons and weight-lifting sessions.

However, boyfriend Rhys Ifans has been constantly ringing her up from the set of his own film, The Boat That Rocked, in Dorset. "Rhys is worried how tired she is. She is really giving her all to this film which is tipped to be one of the biggest of 2009," the Daily Express quoted a friend, as saying.

"But Rhys's voice helps her while she's struggling with the demands. He spends nights on the phone to her trying to soothe her to sleep. His voice relaxes her and he tries to take her through a meditation routine so she can empty her mind," the friend added.