Jake Gyllenhaal is a shape shifter. There is no other explanation. We barely recognised him whilst he was filming 'Nightcrawler', with his sunken cheeks and generally gaunt demeanour, but now he's transformed yet again into a sinewy muscle-man for his forthcoming boxing drama 'Southpaw'.

Gyllenhaal looks completely different to usualGyllenhaal looks completely different to usual

He's never exactly been a typecast actor, but it seems Jake Gyllenhaal can literally perform in any role. He can be unnerving ('Donnie Darko'), not to mention dedicated ('Brokeback Mountain') and now it seems he can manipulate his body in a matter of months. He lost thirty pounds to play the creepy, morally corrupt crime journalist Lou Bloom in Dan Gilroy's latest movie 'Nightcrawler', and now he's picked up his calorie intake and bulked up immensely to play a middle weight boxer in Antoine Fuqua's 'Southpaw'. We only wish we had that much self-discipline!

More: Further proof of Jake Gyllenhaal's dedication to acting...

'Southpaw' follows the life and career of champion boxer Billy Hope, who may be succeeding beyond all expectations in his life's passion, but he struggles to keep everything else in his life from falling apart. The movie co-stars Rachel McAdams, Naomie Harris and Forest Whitaker, and even features appearances from 50 Cent and singer turned actress Rita Ora, who's also set to appear in 'Fifty Shades Of Grey' next year.

More: Jake Gyllenhaal was announced to star in 'Southpaw' earlier this year

Director Fuqua couldn't hide his excitement about Gyllenhaal's forthcoming role in an interview with Deadline. 'Jake is going to change how people see him', he insists. 'I had him training twice a day in the boxing ring, he did two-a-days seven days a week. I pretty much had him with me and my trainer every day... We literally turned him into a beast.'

More: Read our review of 'Nightcrawler'