'Back in the gym': Justin Bieber steams up social media in just a towel showing off his toned abs in two shirtless selfies 

By Sarah Jones and Shyam Dodge For Dailymail.com

Published: 19:48 EST, 16 January 2016 | Updated: 05:29 EST, 17 January 2016

He wowed fans by posting two shirtless selfies on Instagram.

Justin Bieber showed off his muscular physique and toned abs in photos he shared on Saturday in a health club locker room.

'Back in the gym,' the 21-year-old singer wrote as he's seen flexing his muscles while wearing just a towel slung around his waist.

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Baring it all! Justin Bieber, 21, steamed up social media on Saturday in two shirtless selfies

Baring it all! Justin Bieber, 21, steamed up social media on Saturday in two shirtless selfies

The Love Yourself hit-maker has worked hard over the past few years on his body, with the results clear to see.

In January 2015, Justin was signed up as the new face of Calvin Klein underwear, and has since posed in several steamy campaigns.

On Friday he shared a snap as he appeared to be sleeping, showcasing his abs while wearing the brand's boxer briefs.

'Sweet dreams,' Justin captioned the Instagram photo as he's lying across a bed, eyes closed with his head to one side. 

See more of the latest Justin Bieber pictures as she shows off his toned abs 

'Back in the gym': The pop star wrote alongside the photo, as he showed off his toned abs wearing only a towel around his waist

'Back in the gym': The pop star wrote alongside the photo, as he showed off his toned abs wearing only a towel around his waist

The What Do You Mean? singer proudly showcased his fit abs and arms, tattoos on full display against a muscular backdrop. 

His personal trainer Patrick Nilsson previously revealed he had worked hard to maintain the body he needed for the shots.

He told HollywoodLife.com: 'He has put on 20 pounds of muscle and he’s still working on it. It’s a work in progress.'

'We want to put on at least 15 pounds, he’s going to get even bigger, that’s the plan,' Nilsson continued.

His Calvins: Bieber appeared to be sleeping in an Instagram post on Friday, as he showcased his abs while wearing white boxer briefs

His Calvins: Bieber appeared to be sleeping in an Instagram post on Friday, as he showcased his abs while wearing white boxer briefs

It’s not just exercise though that Justin has been using to bulk up – he has also been sticking to a rigid diet.

Patrick added: 'Justin has at least one green juice every day. He usually starts the day with one, he gets them delivered and he stocks his fridge with them.'

'He hated them at first and the way they taste but he loves them now, he loves how they make him feel.'

'It’s the same way with coffee, it tastes bad at first but then you get addicted to it and you start to love the way it tastes, it’s the same with green juice. Justin has one every morning now.'

Shades of purple: Justin, who's been enjoying his fair share of hairstyle switch-ups, decided to add some vibrant colour to his locks

Shades of purple: Justin, who's been enjoying his fair share of hairstyle switch-ups, decided to add some vibrant colour to his locks

After his slumber display, the singer traded up his platinum blond locks for a purple 'do and shared the results on his Instagram page on Friday.

Justin, who's been enjoying his fair share of hairstyle switch-ups, decided to add some vibrant colour to his locks. 

In an Instagram post, the singer, sitting on top of his red Ferrari, proudly showed off his new lilac strands.

On full display: In an Instagram post on Friday, the singer, sitting on top of his red Ferrari, proudly showed off his new lilac strands

On full display: In an Instagram post on Friday, the singer, sitting on top of his red Ferrari, proudly showed off his new lilac strands

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