With temperatures rising, Hollywood's hottest hunks are doffing their tops and unveiling their seriously sexy beach bodies.
Chief among them: Zac Efron, 24, who packed on 18 pounds of muscle to play a Marine in 2012's The Lucky One. "By the end of the movie I didn't recognize myself," Efron, who weighed 145 pounds when production began, later told Men's Health.
The Avengers' Chris Evans, 30, underwent a similar transformation when he bulked up to play the titular character in Captain America: The First Avenger.
"My workout routine isn't too fancy," Evans told Details. "I don't have some cool P90X thing that I do. I just pick up heavy stuff and put it back down. It's really simple stuff. It's like the stuff I learned in high school."
While some stars, like 90210's Trevor Donovan, 33, Real Steel's Hugh Jackman, 43, and Extra's Mario Lopez, 38, have maintained their beefy bods for years, celebs like and Mark Wahlberg, 41, and Colton Haynes, 23, have recently beefed up for new movie and TV roles. "I'm comfortable in my skin," says Wahlberg, who hit the gym hard for 2013's Pain and Gain.
As for Teen Wolf's Haynes? "I do light weights. I like to keep tone as opposed to keep mass. I never skip a day, whether it be going on a hike or running three miles a day. I don't take any days off," the actor recently told Us Weekly. "A lot of people go to the gym for an hour or two hours. I go for half that time but I just like to keep it steady."
Haynes added: "I think when you keep in shape, you're allowed to kind of cheat [on your diet]. If you put the hard work in on that side, you can eat what you want."
To see more shirtless stars -- including Chace Crawford, 26, Gerard Butler, 42, Patrick Schwarzenegger, 18, and more! -- check out Us Weekly's Hollywood's Hottest Hunks gallery now.