It was explain http://www.onemanga.com/Naruto/415/15/, when using sage technique the user gets alot stronger thus making them recover at a faster rate and the fact that Naruto already heals at a faster rate because of the Kyuubi makes him withstand the after math of the rasenshuriken.I am just curious to know how he got around to it not tearing up his arm. He must be using the Sage Chakra somehow to protect himself.