Saitama gets so strong in One-Punch Man through a deliberately absurd mix of “hard work” and meta-joke: he says he trained like a normal human, but the series treats his power as a gag-level, reality-breaking strength.

The official story: Saitama’s training

In the anime and manga, Saitama explains that he became overwhelmingly strong after a simple daily routine done for three years straight:

  • 100 pushups, 100 situps, 100 squats every day.
  • 10 km (about 6.2 miles) running every day.
  • No air conditioning or heating to “toughen” his mind.
  • No rest days, just pure grind, until his hair fell out and he became bald, but gained one‑punch power.

Within the story, this is treated as his genuine origin, and other characters react like it’s insane that something so basic produced a being stronger than any monster.

“He just trained so hard he went bald” is the surface gag and also his literal in‑universe explanation.

The deeper idea: “breaking his limiter”

Later materials and fandom discussions frame his power as “breaking his human limiter,” meaning he surpassed the natural cap placed on human potential.

  • Normal humans hit a ceiling on how strong they can become; Saitama shattered that ceiling.
  • His boring, repetitive routine is a parody of shonen tropes where training arcs unlock impossible power.
  • Once his limiter is gone, his strength keeps scaling to a nonsense, comedic level, letting him beat almost anyone with one punch.

So the why isn’t realistic physiology; it’s that the story treats him as a meta‑joke on overpowered protagonists.

Comedy, parody, and symbolism

Saitama’s power-up is designed less as a serious training program and more as satire:

  • It mocks ultra-complicated training methods by saying the strongest guy just did basic calisthenics and running.
  • It plays with the idea that “hard work alone” beats talent, then cranks it to absurdity.
  • His bald head and plain look emphasize that he’s an ordinary guy with godlike strength, making him visually underwhelming but conceptually broken.

This is why discussions on forums and videos often go wild with joke “theories,” like banana-based power scales or intentionally ridiculous explanations.

Can someone really get that strong from his routine?

In real life, Saitama’s routine is intense but nowhere near planet‑busting:

  • 100/100/100 plus a 10 km run daily would build serious endurance, muscle, and mental toughness, especially for beginners.
  • However, it would not make you fast enough to outpace light or strong enough to destroy meteors; that’s where the parody comes in.
  • Fitness writers analyze the “One Punch Man workout” as a fun challenge, warning about overuse injuries and recommending progression, rest, and variation instead of literally copying his three-year no-break grind.

So you can get fitter and stronger doing a version of his training, but his actual level of power is 100% fictional exaggeration.

Mini timeline of how he got strong

  1. Saitama is a normal, unemployed guy who fails a job interview and feels aimless.
  1. He saves a kid from a crab monster and rediscovers his childhood dream of being a hero.
  2. He starts the 100/100/100 + 10 km daily routine with no days off for three years.
  1. His hair falls out; his emotions flatten because fights become too easy, and he hits “one punch” levels.
  2. By the start of the series, he’s already the strongest being around and struggles more with boredom and recognition than with actual enemies.

TL;DR: Saitama got so strong by doing a brutally simple daily routine (100 pushups, 100 situps, 100 squats, 10 km run, no breaks) for three years, which in the story “breaks his limiter” and turns him into a parody-level, reality- bending powerhouse whose strength is ultimately a comedic exaggeration, not a realistic result of that workout.

Information gathered from public forums or data available on the internet and portrayed here.