Charlie Hunnam takes his workout au naturel!

The actor appeared in tip-top shape for the April issue of Men's Health, but he doesn't owe it all to just eating right and working out.

In fact, the 36-year-old doesn't even consider himself a gym rat.

"I really don't like the environment of being in a gym," Hunnam said. "I'd much rather be outside in the park or you know, go for a nice hike and do some push-ups on a rock or something."

The Sons of Anarchy alum has also turned to Brazilian jiu-jitsu to shape up for his King Arthur: Legend of the Sword role. Along with sword fighting and boxing, Hunnam packed on 20 pounds by strength training. From King Arthur, he delved into The Lost City of Z, in which he lost 40 pounds.

"I'm interested in having a high fitness level across the board. Running, swimming, jumping rope, hiking, jiu-jitsu—I try to do it all," he explained. "I also try to make love as often as I can. That's an important part of fitness. There's no reason you can't be active at 70. I want to run up mountains at that age."

Yep, it's that little tidbit about sex that still makes fans wonder why he couldn't portray Christian Grey.

However, Hunnam maintains that it's ingrained in us, humans, to be active.

"We are supposed to be very active animals. It's our DNA," he emphasizes. "Sweating is how I change my oil every day. I just feel happier, more positive, energized and disciplined if I work out." Ultimately, he says, "I train a lot every day because I'm f**king crazy."