Deku's arms took a beating in the manga. The constant exertion of his quirk caused muscle tears and nerve damage, making it a major challenge for him to continue fighting effectively.
In the manga, Deku's arms got injured due to the extreme stress and strain from his intense battles and using his One For All quirk too much. This led to long-term consequences for his physical condition.
Deku's arms suffered significant damage and exhaustion from overusing his powers.