Read this earlier, but was too busy to reply.
Also saw this video a few weeks ago:
So, when it comes to hook kicks, for showboard breaking and Kyeorugi the ball of the foot is always an option. In order to get that extra reach when needed. And as you can see, in the last kick of that serious of spinning hook kicks the guy uses the ball of the foot.
However, I would like to see those who say that the ball of the foot is stronger, break a thicker board with a spinning hook kick.
Let's take a look at an x-ray. Since I got foot surgery earlier this year I have one handy:
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And at the heel we actually have two areas that we can use for hitting when hitting with the heel in a spinning hook kick. The heel is a massive piece of bone. Furthermore if you hit with the heel you hit the target in a small spot. If you hit with the whole ball of the foot (from 1st to 5th metatarsal) the area you hit is way bigger.
Hitting with the back (red area) - I'd call this the more traditional way:
View attachment 22173
Then there's the way of hitting it with the bottom (red area in the x-ray) of the heel. I'd call this the modern way and I'd say this way is less prone to injury:
View attachment 22172
Now imagine hitting with the ball of the foot:
View attachment 22174
I can see instructors teaching a foot position like in the 2nd and 3rd picture. In order to have less injuries and in order to have the extra reach in competition. However- I doubt there are many people who would consider the ball of the foot being stronger.