Board Thread:Naruto Discussions/@comment-37716482-20181204164454/@comment-30323490-20181204192646

I think it was explained that the user stores its chakra consistently into the seal, even when they are fighting or doing other challenging tasks. So it obviously does require a crazy level of chakra control. Sakura stored her chakra for 3 years before releasing her seal in the war.

As it being the highest level of medical ninjutsu, you do have Naruto's yin-yang release, which can stop the dying effects of the 8 gates and can create human parts from nothing, but this goes way beyond medical ninjutsu and doesn't really classify as such. Other things like Hashirama's healing or nine-tails chakra also don't quite classify as medical ninjutsu, despite being on similar level as Strength of a Hundred Seal.