Aaron Carter has shocked fans after unveiling his extreme new physique online - after revealing his obsession with a gruelling muscle-building regime that's completely transformed his body.

The 22-year-old pop star logged on to social networking website Twitter.com last week, posting a barely recognisable picture of himself menacingly flexing for the camera, and showing off his lean, muscled frame.

Carter revealed he has been holed up at the house of his brother, Backstreet Boys singer Nick Carter's longtime manager, Johnny Wright - and he says chiseling his figure is helping him focus on recording new tracks.

He wrote: "I've been at Johnny Wright's compound working on my mind, music, and body for a new album release!"

Detailing an early morning workout, he added, "ahhhh yawn... here i go again!!!! 1000 pull ups today 7 mile run the 1000 sit ups, i can't stop myself 5:00a.m."