Where did One Punch Man really get this powers from?

Where did One Punch Man really get this powers from?

It was briefly discussed in the scans, he broke his limits imposed by his condition as a living being.

100 push-ups, 100 squats, 10 km every day
i dont think they will ever say from he got his power because it's just a troll anime
lol

You know 100 push-ups, 100 squats, 10 km every day

100 Push-ups, 100 Sit-ups,100 Squats, and 10 KM running everyday. And do not forget about sleeping with no AC on during summer XD

A theory I found was that everyone gets their powers from obsessions they have.
Like, a dude who eats crabs every day will become an evil crab man.

But a crazy excercise regimen every single day?
That'd probably make a one punch man even without the superhero magic.

He really did just that. There's no secret because he's a gag character.
He's like a guy who grinded for hours, days and even years nonstop and got too overpowered by accident. Nobody will do the same crazy stuff as he did because how would they even know that it works?
Saitama was just bored and jobless.