Justin Bieber has assured fans his muscled look in a new magazine photoshoot is all real following a recent row over airbrushing.

The singer threatened legal action after editors of a blog shared pictures which appeared to show him looking less bulky in an advertising campaign for Calvin Klein, and the snaps sparked a debate over whether Bieber's new image had been enhanced.

The Baby hitmaker has stripped off again for a new Men's Health magazine photoshoot, and he has moved to silence speculation by insisting the images have not been retouched at all.

In backstage video taken at the photoshoot, he tells the publication, "You know I'm just getting bigger, man. It's like, my shoulders don't fit in some things... Being on the cover of Men's Health is really, really cool... I love the fact that I got in shape the past two years and I'm finally getting recognition for it. It's not Photoshopped... for all you fools out there saying it's Photoshopped!"

The footage also shows Bieber appearing to lift a weight and posing in front of a boxing bag during the shoot.