[quote=@Dirty Dan]
Hm? How does it already hurt him by using it? I thought that it only hurts him if he tries to blow up 4 story orphanage or something.
[/quote]

That's one way he can hurt himself though that's an extreme example. Excessive use in a short amount of time can cause stress fractures on his bones and damage his muscles. While he is able to diminish the recoil of his own attacks, it seems like it would be a bit much with him having to take hits to use an ability that already causes strain on his body to use.