Ashley Parker Angel Poses Nude: See His Bubble Butt!

"It's incredible how the human body responds and transforms to even just 100 days of a consistent diet and exercise program," the former O-Town singer says

This gives "All or Nothing" an entirely different meaning.

To celebrate the end of his 100-day fitness challenge (which included daily shirtless selfies), former O-Town singer Ashley Parker Angel posed nude in Portland, Ore. "The #100DaysOfFitness challenge may be behind me now but the journey continues," he wrote on Instagram Thursday. "It's incredible how the human body responds and transforms to even just 100 days of a consistent diet and exercise program. During the last 100 days your positive comments motivated me to push through and stay committed. I encourage all of you to experience for yourself how rewarding it is to set your own goals and get inspired by the results."

Angel, who is touring in the musical Wicked, added, "You don't have to be a fitness model or featured in the ESPN Body Issue to be proud of your physique. We all have what it takes to be the best version of ourselves we can be. Be dedicated, be passionate and be relentless in the pursuit of your dreams. Shortly, you will look back at where you started and be astounded at how far you've come...and you might just be inspired enough to post a naked picture of yourself on Instagram."

Last week, Angel, 34, revealed that his goal was to "make lean gains."

"I'm up 12 pounds from where I started," he wrote on Instagram.

Angel isn't the only musician to bare his booty on Instagram. Chrissy Teigen recently shared a picture of her naked husband, John Legend, with her 3 million followers. And who could forget Justin Bieber, who posed in the buff while aboard a boat? The pop star later removed the image, but said he didn't think "it was bad" to show a little skin on social media. The reason for its deletion, he said, was that "someone close to me's daughter follows me and she was embarrassed that she saw my butt and I totally wasn't thinking in that aspect. And I felt awful that she felt bad. To anyone I may have offended I'm so sorry. It was completely pure hearted as a joke but didn't take in account there are littles following me!!! Love u guys." Angel's risqué picture is still available on Facebook, Instagram and Twitter.