Niall Horan pumps iron with his top off at the gym

One Direction star Niall Horan thrilled fans recently when he posted a topless pictures of himself working out in the gym.

The Mullingar native is on the U.S. leg of the band’s Take Me Home world tour.

As well as their rigorous dance routines on stage, all of the One Direction boys have been hitting the gym to make sure they stay in shape during their eight month world tour.

One band insider claimed the boys, Liam Payne, 19, Harry Styles, 19, Louis Tomlinson, 21, Niall Horan, 19, and Zayn Malik, 20, are being limited to a strict diet.

“It’s important for the boys to be in the best shape physically possible for these dates," a source told The Mirror.

“Bosses don’t want half measures, and as the boys spend a lot of time travelling, there can be a tendency to eat junk food and play lots of video games.

“Their trainers have insisted they eat healthier food, and it helps that they had healthy catering for the UK leg of their tour."

The source added: “It’s a great starting point for all the hard work they’re going to have to put in ahead of their stadium tour next year.”