Does kicking itself improve flexibility?

[MadMartigan]

True, but the lack of credentialing is concerning. Snake oil? Who knows.
If everyone can do a 180° split you would see it more often. And used in application. Especially, his explanation using a leg on a chair has zero basis. There is a Ton more mechanics that go on to do a full split.

I have to disagree with your take away from the article. Not because I know the guy, or much about him besides what I'd read in his articles in Black Belt magazine 20 years ago. My understanding is he has a kinesiology degree. Could be bs, I don't know, but the physiotherapists I've spoken to all seem to agree with his 90 degree premise.

The point of the test is only to identify, at a base level, if there are structural limitations preventing that range of motion. He goes on to explain that it takes so much more to actually accomplish the 180 degree splits.
Once you know your body can theoretically do the splits, it's a matter of slowly teaching your nervous system not to lock down when you hit a certain range of motion.

That's what I took away from it anyway

 

[Damien]

My take having done a lot of research into stretching. You have to think about different types of flexibility- being able to be moved into a position and being able to move into a position.

Kicks are a type of dynamic stretching, and will help with the moving into a position. Static stretching is typically done passively, and so is the muscle being moved into a position. You can do static holds at an elevated position though, e.g. leg extended out. This is static, but actively engaging the muscles. All of these are important.

You need passive static stretching to get the maximum ROM, you need dynamic stretching to be confident moving through that ROM under your own power. The static active stretching helps to build the strength of the opposing muscles, whilst you are in a lengthened position which helps your body feel safe (that neurological aspect already mentioned) and obviously helps the body to lift the weight of your leg.

So do all three. I would generally do some dynamics as a warm up, then static stretch <60 seconds per muscle, then kick. You can then do longer statics at the end if you want/have time. Lots of people say static stretching doesn't work, or it increases risk of injury or robs you of power. This is mostly misinterpreted, limited applicability or just wrong information.

The science shows static stretching is the best way to increase max ROM. Stretching for over 60 seconds decreases power, yes, but by less than 5% and that effect quickly disappears with some explosive training. And pretty much every study that says stretching doesn't reduce injury looked at activities like soccer or running where you don't need a large ROM. If you are forcing your muscles into a lengthened position with speed, you'd better have stretched them so that your nervous system doesn't panic, tighten up and cause you to pull something. Dancers know it, martial artists know it, the world of internet and magazine fitness doesn't because they don't do this stuff, and they just look at the headlines of new studies not the details.