(Cover) - EN Star Style - Justin Bieber is intensifying his gym routine in an effort to bulk up.

The 17-year-old teen sensation shot to international fame after being discovered by R&B superstar Usher, and his mix of catchy pop music and boyish good looks has won him hordes of young female fans.

However, the hunk reportedly decided he wants to become more muscular after he spent the afternoon in the gym with British boxer David Haye last month.

The singer who has enlisted the help of a personal trainer - is allegedly planning to hit the gym with a view to transform his slim frame. Justin, who is currently linked to songstress Selena Gomez, is aware of how much his looks have an impact on fans, and hopes to achieve perfect abs in a bid to appeal to the masses.

"Justin knows girls like toned men and he wants that look, a source told British newspaper The Sun.

"He's going to be putting in the hours down the gym to achieve the perfect abs. (C) Cover Media