Here's Maroon 5's sexy frontman Adam Levine's sculpted body in all its tatted-up glory ... and yoga has been the secret to his physical success!

The Voice mentor clearly has muscles, but weightlifting isn't for him. Levine, 32, tells Details:

    "Weights made my neck thick, and I would be like, 'I'm turning into a monster! Yoga takes what you have and molds and sculpts it, which is a much more natural way to look and feel."

Levine says that before shows, he practices an hour of yoga ... and as a result, "I come out physically relaxed."

For those who say Yoga is all about the mind, the "Moves Like Jagger" singer begs to differ. He says, "I don't like how people bullsh-t about how yoga is not about vanity."

Perhaps he'll take his colleague Christina Aguilera to a yoga class one of these days! It may not be "What A Girl Wants" ... but rather, what a girl needs.