Interpreting the body dynamics behind moments in time captured by still pictures is tricky even for those who have background in what is being depicted. For those who lack that background, misinterpretation is common. You're providing a prime example of that.
From what you've said in this thread and in private messages, I'm understanding that by "shoulder rotation" you mean punching (or otherwise striking with the hand) in such a way that the shoulder on the side of the punching arm moves from behind the other shoulder to ahead of it. (For example, starting a right hand punch with the left shoulder in front and ending with the right shoulder in front.)
This is literally the default way of punching everywhere in the world. Martial arts from every country do this and completely untrained fighters do it by instinct. The small minority of martial arts that keep the shoulders completely square while punching have to train their students out of the natural tendency to turn the shoulders.
"Shoulder rotation" is not the most common way to refer to this phenomenon because the motion does not originate in the muscles of the shoulders. It originates lower in the body. The possibilities are:
1) Stepping with the feet (i.e. a lunge punch, moving from a left side lead to a right side lead while throwing a right punch).
2) Rotating the hips, which carry the entire torso (including the shoulders) along for the ride.
3) Twisting the waist, so that the shoulders move further than the hips.
4) Some combination of 1-3.
In the video below, which features Gichin Funakoshi (Oyama's first karate instructor) you can see all the options listed above. (I think some or all of this is contained in DD's video above.)
But ... you ask ... what about all those pictures of karateka with squared shoulders?
Traditional Okinawan karate was largely derived from a southern CMA (possibly Fujian White Crane or something similar) which does tend to work to an unusual extent with squared shoulders. That doesn't mean shoulder rotation is entirely absent, just that it's more subtle. Often the rotation just doesn't go as far as it would in (for example) western boxing. Sometimes the punching shoulder might go from the rear to a squared position - still rotating, just not as far. (Hey - this is why video is more helpful than still pictures. If you see a still picture of someone with squared shoulders, you don't know where their shoulders might have been a moment before or a moment later.) This might be because the older Okinawan styles were close range arts with less room for rotation Not rotating too far might also be emphasized in forms to counterbalance the fact that in the heat of a fight a fighter might naturally tend to overextend.
When Karate travelled from Okinawa to Japan, it transformed significantly based on the pre-existing martial culture. The range become longer and stances became wider. As you can see in the video above, that also led to more pronounced shoulder rotation.
Of course, even if the Okinawan and Japanese karateka were somehow the only people in the world who had never discovered shoulder rotation on their own, (they weren't) that wouldn't mean they learned it from Korea. They could have picked up the idea from countless other sources - Chinese, American, or even older (koryu) Japanese jujutsu systems.
From what you've said in this thread and in private messages, I'm understanding that by "shoulder rotation" you mean punching (or otherwise striking with the hand) in such a way that the shoulder on the side of the punching arm moves from behind the other shoulder to ahead of it. (For example, starting a right hand punch with the left shoulder in front and ending with the right shoulder in front.)
This is literally the default way of punching everywhere in the world. Martial arts from every country do this and completely untrained fighters do it by instinct. The small minority of martial arts that keep the shoulders completely square while punching have to train their students out of the natural tendency to turn the shoulders.
"Shoulder rotation" is not the most common way to refer to this phenomenon because the motion does not originate in the muscles of the shoulders. It originates lower in the body. The possibilities are:
1) Stepping with the feet (i.e. a lunge punch, moving from a left side lead to a right side lead while throwing a right punch).
2) Rotating the hips, which carry the entire torso (including the shoulders) along for the ride.
3) Twisting the waist, so that the shoulders move further than the hips.
4) Some combination of 1-3.
In the video below, which features Gichin Funakoshi (Oyama's first karate instructor) you can see all the options listed above. (I think some or all of this is contained in DD's video above.)
But ... you ask ... what about all those pictures of karateka with squared shoulders?
Traditional Okinawan karate was largely derived from a southern CMA (possibly Fujian White Crane or something similar) which does tend to work to an unusual extent with squared shoulders. That doesn't mean shoulder rotation is entirely absent, just that it's more subtle. Often the rotation just doesn't go as far as it would in (for example) western boxing. Sometimes the punching shoulder might go from the rear to a squared position - still rotating, just not as far. (Hey - this is why video is more helpful than still pictures. If you see a still picture of someone with squared shoulders, you don't know where their shoulders might have been a moment before or a moment later.) This might be because the older Okinawan styles were close range arts with less room for rotation Not rotating too far might also be emphasized in forms to counterbalance the fact that in the heat of a fight a fighter might naturally tend to overextend.
When Karate travelled from Okinawa to Japan, it transformed significantly based on the pre-existing martial culture. The range become longer and stances became wider. As you can see in the video above, that also led to more pronounced shoulder rotation.
Of course, even if the Okinawan and Japanese karateka were somehow the only people in the world who had never discovered shoulder rotation on their own, (they weren't) that wouldn't mean they learned it from Korea. They could have picked up the idea from countless other sources - Chinese, American, or even older (koryu) Japanese jujutsu systems.
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