system
Given the following post, respond as if you're commenting on Reddit:
human
[Spider-Man] How is Wilson Fisk so absurdly strong and durable? Is he a mutant or something?

In the PS4 game, him and Spider-Man are full-on punching each other through walls and shit. Spider-Man's body was changed by a genetically engineered spider but what's Fisk's excuse? Depending on what media he's appearing in, he looks like he weighs anywhere from 500 lbs to well over 1000 and has the strength of ten men. 

Almost every other character like him has some kind of reasoning behind their powers like the X-gene, a symbiote, the venom drug, a science experiment that went wrong, etc. But with Fisk, it just seems like a given. Has this ever been explained or are we to believe that one can naturally achieve those gains in the Marvel universe?
gpt
In universe, you really can get that ripped, or that good with a bow and arrow, or that good with machine guns. "Peak human" (the hypothetical maximum an unmodified human can achieve) includes a lot of feats that border on the inhuman, which in Fisk's case includes turning himself into a walking wall of muscle. 

To date, no one has detected evidence of "cheating" on Fisk's part, even when they had means or incentive to do so. A sentinel has never flagged him as a mutant, Tony Stark has never caught him with a pirated Starktech exoskeleton, no one tried to throw him in the Negative Zone for not registering during Civil War, or otherwise. All seen evidence is that he's just an extremely beefy dude.