Synopsis

There are over 600 individual muscles in the human body. Why waste time training all of them?
In the world of professional arm wrestling, there's only one part that matters: the arm. At least, that's how Chadwick sees it. His commitment to that idea has made him a freak of nature, one whose right arm is large and muscular enough to make weightlifters and strongmen do a double-take. Just how he likes it.
His dedication is rewarded when a strange blue box appears and grants him an ability he'd only dreamed of. Empowered by the system, he's able to exclusively strengthen specific parts of his body. What follows is gains. Lots and lots of gains. And with an ominous portal spewing monsters into his reality, it's not a moment too soon.
Armed with… well, an arm, Chadwick must punch, slap, and smash his way through hordes of enemies and apocalyptic circumstances. What is happening to Earth? Can he protect those he holds dear? Will he ever once think to exercise his legs?
This story is also being posted on Royal Road under my profile (Neviara).
https://www.royalroad.com/profile/302167