True, probably. But as a trope in fantasy movies and illustrations, it makes no sense. I've done a very physical job most of my working life, and got very fit, but I never looked anything like Conan. Years ago, taking a break from a physical job, I decided to lift a few weights a day, and piled on the muscle. Now I've given up my job due to parkinsons, I lift weights as much as I safely can to try to maintain some strength and fitness, and once again I'm more muscular than when I was carrying heavy stuff all day as a job. I maintain, you're not going to get a build like a movie barbarian travelling through the wilderness most days, eating what you can pick from plants and trees and what game you can kill. If you want to look that way, you have to train and eat specifically to look that way.