As per the title, I can't quite see how the upward palm block has any advantage over a normal middle block.
If you are familiar with the ITF patterns it is often used as a direct defence for a fixed stance punch type attack (3rd move from Won-Hyo).
Generally it can be used for any belt line attack - and depending on the positioning and type of attack can sometimes be more desirable than a downward palm block (2 of these at the end of Joong-Gun) For example: knocking a kick upwards may knock the opponent off balance - whilst knocking it downwards may put it straight into your legs (depending on your current positioning).
In your 2 step - as @AndyJeffries explains - the upwards block should leave you in a reasonable position to manipulate the attackers arm after removing the focus of the punch.
It also puts your body in the correct position for the attacker to do their turning kick to a sensible target and gives you chance to practice a block that appears in your patterns (start of Joong-Gun) against a live target.
Note that it is common when doing this in practice to take the block too high - this is one of the reasons it is in 2-step and patterns at a similar grade, giving the instructors/examiners more chance to see and correct this.
We often use the same block in Kukki-Taekwondo during one step sparring for defending against a punch so then we can easily grab the underside of their punching wrist, from there we can quickly apply arm/wrist locks. This is changing in the amount it's used with the new Kukkiwon one step syllabus being more self-defence focused (rather than technical), but still...
The key to understanding a movement's purpose is to consider the previous movement, the next movement, the other hand, the stance, and your eyeline. Since only the other hand, eyeline, and stance is provided in the photo, there can be many variations.
In this case, consider that the left hand is "chambered" into a fist. I don't like the phrase "chambered" because it suggests the hand or foot is in some sort of ready position; in this case, it is not: it is already grabbing something (note the fist), not waiting for something to happen.
The stance is interesting, too. First understand what a stance is, and what it is not. Despite its name (from "stasis"), it is not a static, unmoving thing, you don't just stand there in a stance and that is that.
No, a stance is a mechanism to move the body from one place to another, and also, to help support the execution of a technique. So a cat (or tiger) stance in this case is called beom-seogi, and it's purpose is to load the weight on the back foot. Why? Because the front foot needs to be able to do something. That "something" depends largely on the next movement, which is not mentioned in the picture, but there could be several possibilities: Perhaps the front foot is readying for a front kick; or it could be wrapping around the opponent's leg so that they cannot get out. Remembering that forms also teach us strategy for pain absorption, it could also be that the leg is injured, and this is a means to keep weight off of it. Other possibilities exist too.
So one possible outcome of this technique (again, without the benefit of knowing the previous and next movements), is that our defender is receiving an opponent's grab with the left/chambering hand (that's why it's in a fist; note also the fist's palm is facing upward which supports the grabbing elbow to point downward), and the palm up is issuing an armbar upwards (the palm is facing up, the grabbing fist wrist is palm up); the stance suggests the front leg could be used to engage the opponent's leg to prevent escape from the armbar, or at least to make it difficult. That the defender is looking forward suggests that the attacker is in front, or that is the direction of his movement. This suggests that the front leg from beom-seogi is probably readying for a sweep, which will be facilitated by the arm-bar.
Now, where do we go from here? That depends on the next movement, but again, the beom-seogi is a hint: it allows us to place weight on the back foot, and not commit one way or another to move forward or backward. With an arm bar secured, the attacker can be swept onto the floor requiring an in-place high-fall; or the defender could raise the arm bar assembly, guide it all over his head, then turn counterclockwise; that exposes the opponent's hand to a reverse grip; or a throw requiring a forward roll), or a throw to the ground. These techniques are basic techniques seen in hapkido and aikido (and the exist in taekwondo!). In the follow-up to the overhead pass, Aikido-ka call the resulting techniques sankyo, ikkyo, or gokkyo; I forget the hapkido names, but they are similarly executed.
But in no case is the technique construed to be a "catch" or "block" of a punch. That is sheer ridiculousness: you don't catch punches, you move off the line of attack, because that punch could be a knife or other weapon. And your timing would have to be so spot-on; otherwise, an overly committed punch could work against you as you both tumble to the ground, or, that you take a very hard punch. Even if you entertained one possibility for a punch block, how do you move off the line of attack in a beom-seogi? This example is definitely not a defense of any kind of punch.
So no, the technique has NOTHING to do with a punch in any way.
If you have the full encyclopedia, you'll find further details and illustrations of applications for this technique in the description of Joong Gun Hyung, Vol 9 pages 216 and 222. It's noteworthy that the text says "the palm reaches the target in a circular motion", and one of the photos shows a dotted line tracing the motion of the hand: it should be brought about a hand span in front of the blocking shoulder as the body's squared while stepping the back leg through, then loop outwards to drag an incoming attack outside the line of the body and downwards, circling it inwards again and upwards as the hand comes back on line with the front foot. Dragging the attack sideways first is necessary to stop a kick or punch hitting you, and the circular motion helps unbalance the attacker. You could think of it a bit like a grasping block that doesn't just make a small arc, but loops right round from maybe 11pm on a clock to maybe 8pm, clockwise, though at the end of the movement the hand's not travelling in a side to side plane but move back-to-front.
That said, if someone has attacked deeply enough to hit you, their arm may be extended too far for you to circle it back on line without dragging the attacking limb into your own side. Sometimes it may be practical to catch a punch closer to to their elbow and have your push more directly shove their upper arm towards their shoulder to unbalance them, in which case their arm will bend as you shove it back into them, allowing you to complete your movement on line. The encyclopedia hints at this application in the way a reverse punch has been deflected and the punching shoulder is raised awkwardly.
It may also be possible to a punching arm outwards and have their fist tuck in near your arm pit as your hand slams up under their elbow. But this is diverting into alternative applications of similar movements, and I believe the focus should always be on understanding the utility for the primary application first - here - blocking.
Another explanation of the block that I was taught at one time - but find no evidence for in the encyclopedia, is to catch an attack coming in from your side and throw it up and forwards. For example, if you were stepping through in joong gun hyung to block with your right hand, imagine someone standing off to your right side, delivering a front kick towards your front thigh: you could catch their kicking leg and scoop it forwards and upwards for you - which will be sideways and de-stabilising for them.
I'm using Master Nardizzi's video on palm upward block as reference
I think the block is a circular block as it says and also, possibly, a joint lock as well. My explanation follows:
So, I'm assuming that we're executing the circular block with the left hand in right rear foot stance.
When I begin blocking with the left hand, i'll have my right hand halfway extended.
I think the right hand can be a parry or cover in the case of a hand attack or it can be a gauge in the case of a kick or long, weapon, attack.
The defender is meant to move/shift offline when executing the block ( in practical application) even though, in the pattern, it's executed to something occurring directly in front of the defender.
There is no way, in my opinion, it could be applied to something happening directly in front. The defender HAS to move out of the line of the incoming attack. The right hand, as I've said, is in my opinion, used to a parry/cover from the incoming attack. It may also be used to gauge distance between the attacker and defender. It may also have a distraction function.
It will attract the attacker's eyes whilst the blocking hand's circular motion takes it out of the attacker's field of vision.
In any case once the defender is out of the way they can easily spring the attacking arm/foot up by using the palm to hit it upwards, from underneath.
It's much easier to do this to an enemy's attacking limb when you're at an angle to it.
The defender also grabs the attacker's foot or arm, with their non blocking arm, maybe, by the ankle or the wrist. Then they will pull and twist the attacking limb to break the attacker's balance and body structure as they shift and drop their weight into rear foot stance.
In my opinion, rear foot is used so as to most efficiently shift body weight into the hand executing the circular block. It makes the blocking hand a VERY 'heavy hand' as Chinese martial artists say.
This will, in my opinion, also make it easy to transition, via shifting, into a counter-attacking technique ( Because 90% of the weight is on the back right leg in the case of a, right, rear stance. So the right leg is loaded and thus can be used to power a left pressing kick, or left low side piercing kick or shifting left outward vertical kick or shifting back piercing kick, with the right leg).
The fact that the attacking limb is being held and twisted should aid us in pulling the attacker off balance. So we should be able to easily effect take-downs as well.
It may actually be an effective and relatively, easy technique to apply. But, only if it is applied at the right angle.
It's the angle of execution that matters most, if this block is to actually be successful.
That's what I think anyways. That's my two cents. What do y'alls think? Do you think I'm right?
Ok, I added my own attempt at Bunkai earlier..but...I think.i prefer this one. https://youtu.be/Oekt93vyn5M
OK let me attempt to describe what's happening in the video and then show how it applies to patterns like Joong-Gun that have BOTH palm upward blocks and pressing blocks.
Now, this video ALSO suggests that recent changes to the alignment of the palms in BOTH palm upward block and pressing block with the palms (we're now using straight wrists as opposed to the bent wrists of the past) are in fact WRONG.
Anyway I'll do a quick synopsis of palm upward block as described by Grand Master Nardizzi and then work that description into the Empi Kata Bunkai video above.
GM Nardizzi says the palm upward block technique starts from a relaxed position with bent knees, one foot in front of the other. Then, as you raise your body to wind up for the block, you circle your blocking arm around whilst extending the other arm in front of you. By the time you've finished raising your body your palm will be at it's lowest point and your other arm almost fully extended. Then you drop sharply into rear foot stance, twisting and retracting the other hand to the hip whilst springing up the palm of the blocking hand using the sharp drop in the body mass and and action from the elbow.
Now that's the block, but, how does all that apply to the bunkai video?
OK in Sensei John Burke's video, he's imagining two people facing each other having words. They're in angry disagreement and then one person is tries to leave.
That person is grabbed in their right, upper arm, about bicep level, by the other the other person, using their right arm, in an attempt to prevent the other person from leaving.
The grabbed person is going to do apply a palm upward block with their grabbed right arm. They are going to apply it as a joint lock.
Here's how. First, Sensei Burke extends his non blocking arm by turning the right side of his waist back. This is a natural response to someone grabbing your arm. You will naturally pull away. But this serves a practical purpose of extending the arm of the person grabbing. It helps to stretch their arm out and this makes the enemy's arm pliable. By the way, it's not a sudden jerk. That would make them stiffen their arm. It's a relaxed turn that will allow you to work your enemy's arm.
Sensei Burke's opposite arm is extended naturally (it also serves to push the attacker away if he comes too close and guard from any oncoming punches)
Then Sensei Burke cuts through the grabbing arm by placing his arm under and around it.
NOTE: In order to pull this off your arm MUST be in close contact with your attackers arm as you circle under and around. Your palm MUST be right between his forearm and elbow joint as it goes under and around. If your palm is not in that position, you'll lose leverage and you'll have to apply leverage and brute force via the non blocking arm in order to apply the lock.
But if you do manage to apply the lock. When the lock is complete his upper arm and forearm will be at 90 degrees to each other and your palm should be hooked over the back of his upper arm by virtue of it's being bent over his bicep. Then you drop your body weight into the block thus stressing your enemy's shoulder.
The older way of doing this 'block', with a bent wrist, really does suit this particular application better.
So now you've locked up the enemy with your right arm and he is bent over with back to you. Now, what was your left arm doing whilst all this was going on? Well, it switched from it's initial roles as distraction, maintainer of distance and guard, to it's final role. It's grabbed the attackers left arm or the back of his collar or his hair or the back of shirt sleeve (where the shirt sleeve is sewed onto the rest of his shirt and twisted and pulled HARD as you dropped your weight into the 'block'.
This must just put TREMENDOUS pressure on your attacker's elbow joint, shoulder, back, neck, hips, etc. It probably applies great strain to his entire body. Note if your palm isn't bent backward to hook over his shoulder the 'block'/ shoulder lock is less secure.
So NOW we understand that a palm upward block is most likely a shoulder lock with a highly misleading name.
But WAIT there's more!!
With your enemy bent over like that it's to easy how you may step forward into walking stance or low stance (achieved by stepping forward with your right leg and sliding your left back a little more than usual) and apply a palm strike to your enemy's kidney or the back of his head.
You'd drop your entire weight into his kidney or the back of his head via your left palm whilst holding him in a shoulder lock with your hooked right palm.
The palm strike is best executed with a bent palm as the straight palm is less likely to allow you to efficiently send your weight into your enemy's kidney or the back of his head.
So, there you go. Both upward palm 'block' and palm pressing block are best explained as parts of grappling moves.
Don't go...there's still more!!
Palm pressing block can also be quite helpful in removing grabs to the arm and the palm facing up underneath the elbow of the grabbing arm.
Your body should be at an angle to your attacker, say 30 degrees to him.
Then, you press down with the palm facing down and press up with the palm facing up. NOTE: You would not be pressing STRAIGHT DOWN with the palm facing down nor STRAIGHT UP with the palm facing up.
Imagine you are turning a steering wheel clockwise if your right palm is facing down and anti clockwise if your left palm is facing down. You are turning the steering wheel into the palm facing down. It's an old steering system that has no power steering so you'll have to use your body mass to steer.
NOW, quickly, reverse your hand positions. Your right palm will placed under the elbow and face UP and your left palm will be put inside the crook of the elbow and face DOWN.
Now you're turning the steering wheel the other way!!
NOTE the angle of your body will have changed to the mirror of it's previous angle to your opponent, in order to better apply mass.
You achieve all these changes in position via simple body shifting and changes in hand position. You'll find that you'll definitely be able to get your enemy to release you after the change in position.
It works because you used your opponent's strength against him. When you pressed down with your right palm he resisted by forcing his left arm up.
When you quickly switched positions you surprised him. His left arm was still trying to go upward and your right palm which is now below his left elbow and pressing upward assisted in that motion. Your right palm will help his left palm to go up and away from you. Your enemy will be forced to release you.
So that's it. That's my two cents on the use of palm upward block and palm pressing block. So, I've presented my interpretation of pressing block and palm upward block and their likely functions.
But based on my interpretation, I believe that the original bent wrist positions in those blocks are actually MORE functional than the new straight wrist positions.
That's because I think the bent wrist positions serve a 'hooking' function when applied in a joint lock and a vehicle for effectively delivering mass in a strike or when applying pressure to a hold.
I think I'd use the bent wrist position when actually applying the 'blocks' but what is 'most efficient', for the individual, can be best determined via applying the blocks in 2 person exercises.
What do you think?