In episode 14 season 3 of My Hero Academia we've seen that

Midoriya develops an attack with his legs because his arms get broken more easily when he uses One for All

Why Midoriya arms are weaker than his legs and get broken more easily?


From the start of the season 1 Midoriya always used his arm but since he is not able to control power output that caused his bones to shatter all the time. With the help of Gran Torino he was able to develop Full Cowl but that was not enough. His fight with Muscular was a prime example for that. Thus he again shattered his bones multiple times in that fight and that was the "wait stop" point for him.

Human body can fix fractures like that for an extend but he was using this again and again. So much that even Recovery Girl said "I cant fix you next time."

Therefore if he continue to use his arms with uncontrollable power output they will break to the point of him not being able to use his arms. With the help of Full Cowl Midoriya can use %20 of his power now but that's a recent power up he got. To not risk his arms he decided to find another solution or fighting style. Using his legs was the answer.

In conclusion his arms weaker than his legs because he shattered his arms so many times.


You are missing important thing - Mydoria had never used 100% attacks with his legs.

Mydoria was breaking his arms only when using 100% attacks, and since he was not aware of other ways to use his power early in story, it was happening a lot. Eventually this led to serious damage on his arms, up to the point when any further usage of 100% attacks would cause permanent damage.

This is why he has started to think about alternative ways to fight, and ended up using his legs. But with legs, he was using Full Cowl and iron soles from very beggining.

Therefore, I think it is not fair to say, that his arms are weaker than his legs, as he started to use those in completely different circumstances.

Update: actually, good example of his legs being as fragile as his arms is his academy entry exam - when he used his legs to jump, they've broke just as his arm he used to hit the enemy.

  • Midoriya never used %100 power output. – JustPlain Jul 16 '18 at 7:11
  • @JustPlain by 100% attacks I mean attacks, which are explicitly named in manga as 100%. E.g. 100% Detroit Smash. It doesn't matter if Mydoria is actually using 100% of One For All or not, that's official names. And it doesn't change the point of my answer. – lentinant Jul 16 '18 at 7:17

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