Thursday, 23 December 2010

Balance in the Coronal Plane. Part 1.

As already explained in the articles belonging to the SPC concept section, there are three main body planes: sagittal, transverse and coronal. The latter is very important for movements that happens from the right to left and viceversa because it sets the equilibrium between the ventral (rear) and the frontal sides of the whole body in a given moment.

Balance in our 3-D spacial reality refers to both sagittal and coronal planes. It means we can fall down to each of the four directions N, S, W, E or their multiple combinations. Since we are bipeds with an often used possibility to enlarge our base through spreading our legs wider apart (the bigger is the surface of base the easier is to maintain in balance) it is relatively easy to achieve the goal in the W-E axis (assuming we are facing North at address).
The true balance in golf, however, is surely being set in the coronal plane though. It seems to be quite an easy task when we stand erect motionless. When playing golf we need to be at inclined plane. It means that we need to learn how to counterbalance using our body parts (e.g. the head with the tush) so that the coronal plane always bisects the center of mass area. By the way, this famous losing of tush line issue is in fact nothing more nothing less but subconscious compensations for losing the overall balance, i.e. a subconscious reaction for displacing the line astray.

Note that the coronal plane line is set from the lead ankle joint up because this is where the vertical axis of downswing rotation (that corresponds to the impact phase) goes. Please also note that the pressure areas of both feet correspond with the coronal plane line allocation - as stressed in the diagonal stance articles - ankle joint area of the lead foot and balls area of the rear foot. Lastly, it says how important is replanting of the lead heel onto the ground for overall feel where the axis is.
Let's see how it looks further in the action:

There are a lot of problems if we are off balance during the motion. Our sense of balance is disturbed and calls for compensatory moves aimed at regaining balance that usually spoil the final effect of the action. That is why our understanding of how we can benefit from merging center of body mass with the coronal plane line may be crucial. Feel and anticipate where it is during setup while placing your lead feet - watch how carefully Mr.Hogan does it in the 'Setting the Swing Motion' vid.

Wednesday, 1 December 2010

Setting the Swing Motion

One of my friends from golf fora used the notion "setup dependent swing motion". I believe this excellent definition says everything. All conscious thoughts should be used during setup routine in order to leave as less biophysical options as possible. We have already described in detail such concepts as the diagonality of the stance, building the firm rear side from the ground up, biokinetical grip, low plane angle, etc. but we have not described how a biokinetically correct setup routine should look like.

I would like to begin with goals that must be fulfilled thanks to the setup dependent action:
1. optimum conditions for most effective kinetic energy flow;
2. optimum conditions for undisturbed balance;
3. optimum conditions for automating the motion.

Let us discuss the most basic stuff for the beginning:

ad.1. First, we must be able to create sufficient amount of energy in order to think about efficient release; hence the necessity of optimalizing the backswing phase that have to ensure a long enough arc of the clubhead but with distal parts subdued to the main body (BTW, if our goal is to start in ReMAX LD champs - the means would be a bit different). How we can do it ?
First, by closing the feet line; putting the rear foot back to the rear vividly contributes to make the arc longer without necessity of swinging the arms above shoulder plane and losing connection with main body. Secondly, by setting the rear foot perpendicularily to the target; it will make the transition more powerful and enhance the linear part in the pelvis area via horizontally oriented forces (creating torques); thirdly, by flaring the lead foot out; it will be the best help in enhancing the rotary part of the downswing when the linear shift has been finished.
Next, the hip and knee joints must be set properly so that one could use also vertically oriented forces efficiently.
The grip should be set the way the leverages in wrists joints (the most important ones by far) could be used most effectively; hence the concept of merging lead wrist deviation with rear wrist flexion.
Lastly, waggling the club not only relaxes joints, ligaments and muscles but also helps in establishing the best grip in a very dynamical process. One should not grip the club tight before last waggle is being finished.

ad.2. The surface of feet is very small in relation to the whole body mass, especially in a dynamic motion, thus, feet must seek for wide enough stance in both planes (South-North and East-West). The bigger surface the base has the easier is to be in balance through the motion and, what is even more important, the easier is to use the ground shear forces comparing to when all body parts are in line with each other.
Secondly, knee and ankle joints movements must be utilized both ways; during the backswing, lead heel shouldn't be kept flat on the ground; lead knee shouldn't be kept stiff from bending inside in a due moment; same with rear foot that shouldn't neither be spun out nor kept on the ground approaching impact; therefore, we need to relax these jopints properly when taking our stance - even if it require replacing feet several times.
Next, the head, what is a relatively heavy organ - the weight of it amounts to ca. 7.5 % of the whole human body weight; moreover, it is the most distant part from the human body CoG (which is in navel area - for an adult man; for an adult woman - a bit lower, BTW) that makes head's motion impact on ANY CoG shift even bigger. Hence a very useful notion of the stationary end of cervical spine (not stationary head, which is a biomechanical error in thinking). Also it is worth mentioning that head should be st depending on the eyedness - but this is just a microscale issue.
Last but not least, all thre main horizontal planes, i.e. feet, hips and shoulders should never be parallel to one another. Hence the idea of increasing the diagonality of the stance in three planes - hips open in relation to feet, shoulders closed in relation to hips. Of course shoulders are used for visual aiming while feet seeks for ultimate balance and ultimate benefitting from ground forces.

ad.3. First, the firm rear side from the ground up must be build at setup thanks to the rear ankle and knee joints preset. The action contains a clockwise turn of the rear ankle and knee joints without changing the rear foot square to the target line position till the limit. Turning the rear heel outwards first (this makes the foot perpendicular to the target) and then turning out both joints. Like one wants to bring your rear heel inwards again, which won't happen because of shear forces between the foot and the ground. Since e.g. the rotational RoM of ankle joint is much smaller of that of knee joint and the latter is much smaller that this of hip joint, etc. - the sequentiality of reaction for torques is established perfectly from the ground up without leaving any other option left. The rear elbow joint may or should be preset as well so that there are limited chances for an independent from the main body movement of arms.

For the visualization purposes, we shall use again a great vid of Mr.Hogan from his Shell match against Snead here:

If we are to depict the setup in chronological points, I believe it would be like this:

1. setting the clubface perpendicularily to the intended target while visualizing it;

2. waggling the club so that the muscles, liganments and joints are relaxed as well as setting the correct position of the rear hand in relation to the lead one on the grip;

3. aiming at the target with shoulder blades while setting hips and independently lead and rear foot in their desired positions (hips a bit open in relation to shoulders, lead foot more flared out, rear foot less flared out, rear foot backed in relation to the lead one); the first motion is always done by the lead foot as the rear one takes its position in relation to it; feet are being lifted off the ground alternately; it is worth noting that lead foot is being put sequentially, from toes to heel while the rear one practically is being put on balls, leaving the heel barely touching the ground; it perfectly corresponds with feet pressure points areas;

4. waggling the club with mental image of the shot so that its trajectory and shape could be visualized;

5. fine tuning everything together; again, lead feet first (as the one that corresponds to the fixed ball position for all clubs and setting the area of the downswing vertical axis of body rotation) and the rear following it setting the correct width and depth of the stance; "getting into the shot"; presetting the rear ankle and knee joints via setting the rear foot perpendicular to the ground; presetting the elbow joint of the rear arm via putting the socket up;

6. putting the clubface behind the ball and starting the motion via targetwise trigger compression.

With a solid and wise setup routine no doubt it is much easier to make the motion consistent and repeatable. The serious key for automating the motion.

Sunday, 21 November 2010

Ground Forces, Feet and Pressure Points

Ground forces create two kinds of motions - horizontally oriented and vertically oriented - as the orientation of forces can be horizontal or vertical as well. The latter are simple forces appearing thanks to altering our weight. It is very useful here to remember that the notion "weight" is always equal to a force:
- "statically" = your true mass x gravitational acceleration;
- "dynamically" = your true mass x gravitational acceleration +/- additional acceleration.
Vertically oriented motions happen because the weight changes, e.g. when you prepare to jump you create additional acceleration acting in the same direction as gravity, therefore, your weight changes which can be observed on the scales (with some delay though if we talk about mechanical spring scales). What always remains unchanged is mass.
Horizontally oriented motions are being induced thanks to shear forces that exists because of created torques in the hard structure of human's organism. The linear part is not being induced by the spine but by human's body response to simple physics ocurring from the ground up. Shear forces are strong enough to create torques that move the pelvis area targetwise. What happens with the spine as e.g. the secondary axis tilt is a consequence of this scenario. We already know very well (vide: the SPC concept) that automated targetwise CoG shift is totally dependent on what happens below pelvis and, consequently, on horizontally oriented forces.
Feet should be aware of and prepared to feel both types of forces. The optimal combination of horizontally and vertically oriented motions forces that there exists the optimal distribution of pressure points of feet. We remember from the Diagonal Stance concept that the surface of the feet is relarively very small comparing to the mass of the whole body, especially in a dynamic movement and, therefore, both feet should never be placed in line with each other in 2 basic dimensions (lead foot flared while rear one square to the target, rear foot taken back in relation to the lead one - both rules better visible the longer the club is).

The Diagonal Stance diagramme shows the pressure points of both feet at address. What is not without importance, practically the same allocation of the pressure points occurs at impact. Let us present what happens during the entire motion in this sphere:
The red rectangles shows where the pressure is being allocated, white arrows shows the horizontal orientation of the torques (red arrows shows the same but without interaction between feet and the ground) and the white dots shows the vertical oriented forces.

At setup, we need to ensure the firm rear side from the ground up via presetting the rear knee and ankle joints. The lead side uses only normal (vertically oriented) forces. The relation between the line joining most important pressure points of both feet (point under lead foot ankle joint and rear foot's balls area) and the target line is dependent on how closed is the stance, i.e. how long is the club one actually is using (according to the D-plane principles).

During the backswing phase, the pressure point of the rear foot gradually moves to the heel as the rear leg straightens and rear hip joint goes up and back. The preset done at address still exerts impact of torques that affects the rear side. The lead side being passive starts to correspond to it parallelly.

At the top, overtorques of the rear side joints set the direction of the automatic linear shift to the S-W (assuming we are facing North at setup). The lead heel rolls up and loses contact with the ground preparing to establish the new downswing vertical axis of body rotation. Lead heel will always come off the ground unintentionally if the pelvis works in a slanted way (at 45 degrees up & back with the whole body and arms working together) and there is a proper sequencing (the lead side is totally passive during the backswing letting the lead knee joint bent inside). The lead heel should replace at least the same spot, or better a tad closer to the target because of the vertical axis of rotation linear shift to the front side of the body in a perfect world so that the dynamics of the motion is utilized most efficiently.

After the linear shift has been done and the vertical axis of downswing rotation has been established the main pressure point of the lead foot goes under the lead ankle, i.e. where the lead heels hits the ground. The rear side becomes to be passive and inertial, thus, the pressure point of the rear foot goes entirely near the inner edge. There is a slight impression of targetwise pushing from the rear foot since the overtorques have already been released and the pressure point stretches from the heel towards toes. The lead side uses the vertically oriented forces during the phase of pure rotation since the natural limitation in the lead ankle and knee joints has not been reached yet.

At impact, the horizontally oriented forces start to act, or better said, to accompany the vertically oriented ones, due to the process of releasing the stored energy which can naturally happen thanks to appearing strong torques in the joints. The rear heel rolls up and loses contact with the ground and the entire rear foot starts to spin out.

After the energy has been passed to the ball, the ground forces start to be of lesser importance. The lead foot spins out together with further post-impact body rotation while the rear foot loses contact with the ground almost entirely and often is being dragged - almost, i.e. there is some pressure left near the toe because of balance reasons.
The above visualization is totally in line with the SPC concept. For a more global view please go to the section where and compare coresponding phases of the swing motion.

Saturday, 20 November 2010

Ben Hogan's Masters

Ben Hogan's post-secret swing motion is rightfully the most respected one in the history of golf. He became the best ballstriker of all times despite countless serious adversities he had to face with in his life. Hogan was supposed to have developed himself a secret or secrets thanks to his genius and hard work - however, even he had his masters whom he learnt concepts from.

Wild Bill Mehlhorn - one of very few Ben Hogan admired and learned from in his early days. Hogan even said that Wild Bill was the best from tee to green he ever saw. It can be easily seen that such things as the trigger compression, sequential swinging from the ground up or the diagonal stance was being present in Mehlhorn's motion. Observe carefully and pay special attention to the way he set up before starting his swing. It is very obvious that Mehlhorn must have been very aware how to benefit from the ground forces.

Henry Picard's name is very often associated with young Ben Hogan. Picard was known for his generosity to other players, and Sam Snead credited Picard with convincing him to turn pro. Picard also offered to bankroll Ben Hogan when Hogan was struggling, then got Hogan into the field at the first tournament Hogan would win. He also helped Hogan eliminate his hook, and Hogan dedicated his book "Ben Hogan's Power Golf," to Picard. From this short material presented below we can easily see how similar was the kinetics of Picard's pelvis area motion to that of the best ballstriker of all times. Pay special attention to his rear hip joint linear motion at transition - it is a great example of the SPC concept in the pelvis area. Also it shows how important from the mechanical point of view is passive lead side during the backswing phase; Picard's lead heel does not stay on the ground as well as his lead knee bends inwards helping to set the correct CoG pelvis area shift and making the transition almost automatic.

Macdonald Smith - Ben Hogan was being said to get his famous pronation technique from Smith's marvellous pivot guided swing motion. Smith's action was the most observed motion in the hickory era. Pros studied his swing pretty much similarily to later colleagues standing for hours on range observing Hogan's sessions decades later.
Please take a look at 1:03-04 of the video (01:18:43-01:18:44) that looked exactly like Smith was just creating the firm rear side via rear ankle and knee joints preset described in the SPC concept. Look at the waggle, too. And the diagonal stance. Not mentioning more obvious things like trigger compression or low plane angle. Indeed, if someone had a good eye and had analytical mind a lot could have been learned from Smith. Mr.Hogan surely did.

Ben Hogan took a lot of inspiration from baseball swing motion. Low plane, perpendicularity of distal limbs to the core, active stance that makes both legs and feet live their own lives and great kinetic sequentiality from the ground up - just to name a few similarities between great baseball swing and this of the greatest ballstriker that ever lived. It is widely known that Hogan met both Byrd and Williams for numerous times and asked them about motorics of baseball swing motion.

The above examples would not solve all mysteries that accompany Ben Hogan's secrets. But surely they will give an excellent picture of the background as well as underline many common points that were present in the biokinetically almost ideal post-secret Hogan's swing motion.

Monday, 16 August 2010

Low Plane Magic

The biokinetically soundest relation of the arms and the main body is when arms can work perpendicularily to the core. Of course, it can happen only in certain phases of the motion because of human's body nature. One of these phases is the backswing top where the entire lead arm should exactly be perpendicular to the spine (and the rear humerus is parallel to the spine). The shoulder line should be perpendicular to the spine as well which means that the lead humerus is pinned to the chest and can work together the main body automatically. A sort of one plane backswing position where there are no excessive flatness or uprightness of the plane - because of the square relation to the core.

According to some golf myths such a position on the top is often being called erroneously "flat". Upright two-planish backswings never give such a possibility since the lead shoulder joint alone is too weak (in the sense - too unsecure) a connection with the upper body to guarantee a simultaneous work. Here we can use the word "upright" because the square relation between lead arm and the spine has been destroyed.

Another popular myth is that the plane height should be dependent on a golfer's height. It is just absurd since what eventually matter are body proportions - but we can even forget about it if we assume that the proportions between well-fitted clubs and a golfer's body are stable in the macroscale. There are really no arguments to think otherwise.

Today's golf instruction does not often understand biokinetics and sometimes find ridiculous arguments against low plane golfers while the truth is that the vast majority of the best ballstrikers in history of golf were never upright players. And even if some of them might have been, they were capable to shift back beautifully to the low plane during the downswing (vide: the EEP concept). However, this procedure is just a waste of kinetic force and one does not need to be a genius to state that the best scenario is when necessary plane shifts are as small as possible - from elbow plane to the shoulder plane at the top and to the elbow plane as soon as possible in the downswing (where the rear forearm becomes perpendicular to the core).

Mr.Hogan was right again with imagining the swing plane being not higher than the pane of glass resting at his shoulders. Too bad many people do not understand his intentions...:

And here is the video that visualizes the concept:

Thursday, 3 June 2010

Lead Heel Biokinetic Dance

It is one of definitely the most forgotten things from the past that has a lot of merits that today's instruction wrongly neglects.
Lead heel will always come off the ground unintentionally if the pelvis works in a slanted way (at 45 degrees up & back with the whole body and arms working together) and there is a proper sequencing (the lead side is totally passive during the backswing letting the lead knee joint bent inside). All great ballstrikers of the former years did it, from Vardon through Jones, Snead, Hogan, Middlecoff, Lema, Nicklaus, Trevino, Moe, etc. - the longer the swing arc the more visible it is - it vividly helps in achieving a full coil of the body as well as emphasize setting the vertical axis of downswing rotation in a correct time and place. Of course, we cannot forget about the correct weight transfer to the rear without which it would be difficult to expect the lead heel biokinetic dance, so to speak.

Somebody could ask - what about the theory of natural body limitations then ? Shouldn't the lead side limit the movement ? The answer is - the theory of limitations works best if it is not against physics. The firm rear side built sequentially from the ground up creates the natural human body limitations - while the lead side must be passive during the backswing so that it takes the lead later on when the orientation changes. Simple as that.

The lead heel should replace at least the same spot, or better said, a tad closer to the target because of the vertical axis of rotation linear shift to the front side of the body in a perfect world. If the heel replaces closer to the golfer's rear side most probably there is a spin-out in the pelvis area suggesting there is not enough big CoG shift. It also would depend on how much the lead foot was flared out in relation to the target line.

Lastly, one shouldn't forget that the pelvis motion is dependent on what happens below hip joints - and how the soundest biokinetically pelvis area motion looks like - please look at it through the prism of the lead heel motion. As we already know from the SPC concept descriptions and visualizations, the human pelvis motion during the golf swing always includes linear and rotational elements. We also know that the biokinetically soundest is to let the linear motion preceed the rotational one. Now, since noone on Earth could start the downswing properly with the lead heel off the ground - the heel must be replaced - and in order to do so, the linear part must be performed. After the heel is replanted all the golfer needs is the sequential rotation of the whole body system from the ground up. The biophysics is really simple as that. Too bad the modern instruction is so much blind at such wisdoms. Hopefully, it will change someday.

Look at the SPC pelvis area diagrams and confront them with what you have just seen:

As you can see on these diagrams, the rotational part always follows the linear part which is a biomechanical necessity for a bipedal. The key is to automate the cascade of events - both thanks to the theory of limitations - the linear part thanks to physical reaction and the rotational one thanks to anatomic reaction. The power of biokinetics.

Wednesday, 19 May 2010

Old Mr.Hogan - still biokinetically the soundest

All of us saw the famous "beach" clip where old Mr.Hogan shows how to swing to his friends. However, not many of us try to go deeper into his outstanding presentation and to find certain biokinetic lego pieces that were present in all post-secret swing motion of Ben Hogan.

I have already sacrificed some videos (published on YouTube) to these lego pieces describing them in detail on base of Mr.Hogan's (and also other greatest ballstrikers') action. Now, we can see the great man performing all of them even when showing his swing purposedly in a slo-mo ! Trigger compression, diagonal stance, biokinetical grip, firm rear side creation, swinging from the ground up, early elbow plane, etc. - all were there on the beach together with Mr.Hogan and are here with us all forever now.

Please watch this vid carefully:

 If anyone has still some doubts, now it is very easy to confront everything together. There is no bright future for the golf instruction without biokinetics and biomechanics. Mr.Hogan knew it as the first long time ago and became the best ballstriker in the history of golf. We are in the 21st century now and it is highest time to cut the horrible break and to start to continue Mr.Hogan's work in modern times.

Thursday, 15 April 2010

The Early Elbow Plane

The EEP (early elbow plane) is a logical result of benefitting from one of the golden rules of (bio)physics concerning the perpendicularily of the distal parts motion to the spine (core).

The EEP is a description of a biophysical phenomenon when a classic double shifter achieves the EP relatively very early in the downswing with the shaft bissecting the forearm; a decent amount of lag is necessary to perform the EEP. An EEP golfer receives full support from both rear humerus (in relation to the body alongside with which is moving) as well as from rear forearm that supports the shaft and clubhead until impact being in-line with it and at a perpendicular angle to the core.

The best example is post-accident Hogan who achieves the EEP very early in the downswing (his rear elbow moving forward early and fast after transition) until shaft becomes in-line with rear forearm and rear forearm perpendicular to his core. From this moment there is his turning main body only, the rest is in status quo in relation to it which may be certainly considered as the best possible biomotoric scenario for consistency in the downswing phase:

As we already know, the backswing must be lead by the rear side, for the reasons mentioned earlier. It won't let a too inside takeaway which is the main enemy of flattening the shaft plane after transition = one of the biggest enemies of the downswing EEP. The best results are achieved if it is being performed sequentially from the ground up at ca. 45* angle up & back. The downswing phase occurs sequentially from the ground up as well thanks to an automated transition that is possible thanks to finding limitations in the joints sequentially from the ground up. The overtorques in the joints cause the trampoline effect when changing the orientation of the motion (from backswing to downswing). The lower the body part the sooner it finishes backswing and the sooner it starts downswing. It creates optimal condition for the plane to drop (congruently) from TSP to EP as soon as possible.

The Diagonal Stance

I am of the opinion that the feet should be in the diagonal stance position always when the pelvis area motion happens, no matter what is the length of the club. Practically, only putter stance would require a square stance, since we do not need any hip joint motion. In order to achieve it the rear foot ball should be in line with the lead foot heel, therefore, sort of diagonally to the target line. Of course, this position is offsetted via different feet position - the lead one is flared while the rear one is square to the target line.
This diagonal stance has one more very important merit, in my opinion. When the downswing progresses, the rotational aspect relocates gradually the CoG to the lead foot heel. At impact, the CoG line should optimally run from the knee joint to the ankle perpendicularily to the ground (letting the knee joint maintain some flex necessary to allow the joint to rotate and guarantees the best possible stability). It is not already at the heel but definitely is closer to the heel than to the toes. The opposite scenario happens with the rear foot where the heel loses its contact with the ground first, maintaining the contact in the area near ball/toe. Now, when we create an imaginary line between those contact points of both feet it can be parallel to the target line only when feet are placed in a diagonal stance position. This creates a necessary torque, since the hips are already open at impact, does not allowing to transfer the CoG too early to the lead heel (causing the lead knee to straighten too early). The same torque does not allow the weight to be left on the rear side too long as well.
Of course, the smaller hip area motion is required, the less diagonal stance is necessary.

Last but not least, the diagonal stance gives a much better base for a human body weight. The bigger surface the base has the easier is to be in balance through the motion and, what is even more important, the easier is to use the ground shear forces comparing to when all body parts are in line with each other. Human feet are very small in relation to the entire body mass that they must keep in balance, especially during such a dynamic motion as the golf swing is.
Here is the diagramme of the Diagonal Stance. The blue line is the target line, the red squares are the address pressure points of both feet and the red lines are linking the pressure points setting the feet (see also the blog part dedicated to feet pressure points where everything is explained in detail):

The above diagramme is, in fact, a corrected version of the original Hogan's stance diagramme published in "5 Lessons":

Watching thousands of Hogan's clips (as well as some other great ballstrikers - George Knudson and Mac O'Grady come to my mind first) I consider the DS concept as much closer to reality than the latter diagramme. As Mr.Hogan's friend and playing partner, Gardner Dickinson said "[...] he experimented with putting some wrinkles in his left wrist. Ben gradually changed his grip so that his left hand showed about one and a half knuckles at address. At the same time, he let the right hand move more on top of the shaft so that the "V" formed by his thumb and forefinger pointed between his chin and left ear. He then moved the ball forward in his stance, and repositioned his hands at address so that they were about even with the ball, or even slightly behind it with a driver. Finally he assumed a distinctly closed stance at address, even on pitch shots, by withdrawing his right foot from the intended line of flight. Ben aimed with his shoulders, not his feet, so the closed stance had minimal effect on his targeting."

Jackie Burke likes to call the concept "runner's stance" underlining the dynamism of a static position. If you imagine how would a runner stand ready to start the race next words are not necessary at all.

Mr.Hogan's (and other great ballstrikers') stance allowed to locate the downswing vertical axis of rotation in the same place towards the lead ankle joint; the rear foot moves back the longer the club is, makes it finding the bottom of the arc earlier.
A flared lead foot allows to find the limit of rotation of the lead knee faster than the rear one. The knee that cannot rotate further bends inwards what almost automatically makes the weight shift on a lead hip joint when the linear CoG shift happens. If the lead foot is put inward, instead flared, all tension in the knee and hip is lost. Moreover, the sum of small X-factors is being achieved properly when the lead hip "stays" early in the backswing allowing the rear shoulder find its limit without making the backswing too long and loose. Lastly, during the downswing it guarantees a proper correlation of the pelvis position and the impact position. Hips are open at impact, thus, the lead foot should not be square to the target in any case if the aim is to ease the rotation.

Watch Mr.Hogan sets his feet in search for a ground forces and totally balanced motion with the lead foot always flared out and the rear one perpendicular to the target:

Observe how Mr.Hogan seeks for a stable stance that would guarantee the most effective usage of the ground forces. A closed toe line, open hips and square shoulders (in relation to each other), a flared lead while a squared rear foot plus different pressure points for both feet - these are the real keys.

Closed feet, open hips, squarish shoulders = the essence of the diagonal stance. Other words - shoulders are closed in relation to hips but open in relation to feet. Hips are (strongly) open in relation to feet and (less) open in relation to shoulders. Feet are (strongly) closed in relation to hips and (less) closed in relation to shoulders.
Imagine one wants to start a sidewise dynamic physical activity directed at West (assuming one faces North at stance) - can be hammering a nail at the West wall or starting to run to the West, or whatever - the diagonal stance will be chosen best by ones subconscious mind as the most effective one. Hogan knew it and, by an occasion, it appeared to be the best possible stance type to apply D-plane consequences with the fixed ball position (which is a very huge convenience for a golfer if one does not need to think about 14 different ball positions).
Simply ingenious statically and dynamically.

The intention is setting joints the way it is useful both for backswing as well as for downswing. That's why Hogan's diagonal stance is pure genial thing, who knows, maybe the most important thing ever. The rear foot is being settled the way it helps to automate the transition while the lead one to support the vertical axis of downswing rotation the best possible way, i.e. having the mass vector going down through the ankle joint or ensure continuous rotation during the impact zone.
Besides, both feet position match the relationship between hip joints and feet separately in both planes, sagittal and coronal during the setup - on the level of subconscious mind. Rear foot matching backswing while lead matching downswing. It is heavily linked to the process of independent setting of both feet at angles:

The Sagittal Plane Compression Concept. Part 6.

It is very important to underline that the crucial thing when seeing the motion through compression and expansion elements is to understand that the expansion elements are framed within compression ones. I mean there is no expansion that does not begin and end with a compression. That's why the working name of the concept is the Sagittal Plane Compression and not the Sagittal Plane Expansion.
This concept reflects a perfect example of creating and using the kinetic energy in the swing motion. The compression allows to store energy and pass it to the passive side of the body sequentially from the ground up which can happen only when the orientation of the motion corresponds with the active side of the moving body.

Compression is being controlled by the natural limitations of the human body based on stable skeleton/joints structure. Muscles that are generators of the energy cannot be used to control - they must be controlled by something stable. The joints won't let the muscles waste the energy while they find their natural limitations during the torquing process. Moreover, they will allow to react into the opposite direction using the same energy since the limitation is one-sided only - as e.g. during the transition providded there is a weight shift to the rear side with preset rear leg joints (bouncing wall effect).

Expansion, as a process always enframed between two compression phases, is in fact being controlled by those compression phases of the lower located parts of the body (vide: transverse planes). I know how silly it sounds but actually this is what happens. It won't sound silly if we take into account that the compression/expansion phases occur sequentially in time from the ground up. For instance - the transition - when the legs have finished their transition compression and are already in the expansion phase, the pelvis actually is in the middle of its transition compression and the upper body is still in the backswing expansion phase. The chain of events works by itself almost automatically then. Say, the expansion phase of the body part that is located higher meets the compression phase of the lower located one which won't let another scenario to happen unintentionally.

What is also of big importance -- pulling vs. pushing issue. Each compression phase requires taking the momentum over by the other sagittal part of the body fluently. It can be done only via pulling from the core out. However, the smaller is the gap to the next compression phase (or by the end of the expansion phase) the more pushing instead pulling occurs -- as pulling converts into pushing with the momentum already rocked on. The leading side starts to push it as pulling would guarantee no further acceleration.

Observe how Mr.Hogan builds the frim rear side sequentially from the ground up thanks to the rear ankle and knee joints preset. Observe how his rear hip reacts unintentionally to the sequentially built torques and moves linearily. Observe how Mr.Hogan can ensure automatically that the downswing is a pure undisturbed rotation as a natural consequence of what has just happened before in the motion or even during the setup.

Mr.Hogan's whole swing is a beautiful compilation of compression and expansion phases that occur in a proper sequence from the ground up thanks to properly built torques in the joints.
As we know it is called a Sagittal Plane Compression (SPC) concept:

How the firm rear side can be achieved automatically in practice ? Observe closely Mr.Hogan's rear feet action at setup in this video:

The action contains a clockwise turn of the rear ankle and knee joints without changing the rear foot square to the target line position till the limit. Turning the rear heel outwards first (this makes the foot perpendicular to the target) and then turning out both joints. Like one wants to bring your rear heel inwards again, which won't happen because of shear forces between the foot and the ground.
One should imagine that when standing on ice your rear foot would spin outwards because shear forces are practically not present. Since there are a lot of shear forces between one's foot (armed with spikes) and relatively soft ground, a substantial amount of torque is being built. One will feel the torque. One will also see that your rear knee joint bends slightly inwards as a consequence of this action.
It is one of the most importants little secrets of Mr.Hogan aimed at building the firm rear side from the ground up that, consequently, leads to automation of the whole motion.

Here is the photo of the BGST author presenting rear ankle/knee joints (BTW, as well as the rear elbow joint) presets:

The arrows show the torque vectors while the blue slanted line shows the natural reaction of the knee joint to the process of its presetting. The bending inward is an additional help when building the firm rear side from the ground up.

The Sagittal Plane Compression Concept. Part 5.

The main goal of the SPC concept is not only to automate the golf swing motion but also to ensure that the kinetic chain of events is being built and released properly. While understanding how the energy is being created is relatively easy a task, the most confusing aspect is the releasing of the stored energy up to the clubhead - mainly because there is no change in orientatiuon of the motion.
Actually, it is a very simple phenomenon that allows to release the whole kinetic chain in a proper way and is a very important part of the SPC concept called the second (impact) compression.
In order to understand it well we must differ the two scenarios - a. compression phase that is aimed at the change of orientation (direction of movement) and b. compression phase that happens without the change of orientation (direction of movement). The first one of course happens between backswing and downswing, while the second one happens at impact when the whole kinetic chain is being released at the ball. The chain is the whole human body starting from the ground/feet ending on the arms/hands/clubhead. The release is just passing the stored energy to the more distal parts of the system and it is done via consequent stalling of former links in this chain - i.e. in order to pass the energy to the arms, the main body and the shoulder joint must stall.
But during downswing nothing can stall because the body is in constant rapid movement till the finish. So how to pass the energy to the arms ? Look at this photo sequence:

The ball position indicates vertically when the chain is being released correctly. It means that the lead shoulder should (hypothetically) stall at this line in order to let the distal limb and, consequently, the clubshaft and clubhead to release the energy and achieve the peak velocity. If the lead shoulder continues to move linearily to the target in a 2-D, the chain wouldn't be released at all.
However, if the lead shoulder, which must be still in rapid motion, stops to move horizontally and starts to move vertically up (say, on the red line up) in 3-D, so the chain must be released because its position in relation to the ball does not change in the horizontal 2-D sense - say, the ball "sees" the lead shoulder stalls completely.

So, as we can see, it is really a very simple physical phenomenon that allows the compression phase to occur without stopping the motion and without changing the orientation of the whole movement. Moreover, it guarantees automatically that the angular velocity of the clubhead (as the most distal part of the system) increases as per parametric acceleration phenomenon. The second (impact) compression phase:

Another crucial element of the SPC concept worth special mentioning is the Trigger Compression.
The backswing is biokinetically sound when its being lead by the rear side of the body in the sagittal plane - it is biomechanically most efficient if the side that leads should have the same orientation of motion.  After addressing the club, the best ballstrikers triggered the swing with the rear side push targetwise that simply provide initial inertia and guide to pull the entire rear side back and up at 45* angle while maintaining spine angle till natural limits sequentially from the ground up. The initial trigger compression also clears the way for subconscious mind, so to speak. It rocks all the motion and put it into work smoothly and correctly.
Otherwise -- how one could start the motion without conscious mind engagement ?

Moreover, every motion benefits physically from a move aimed at rocking on the motion. This is what the trigger compression does for a golf swing. And it is not just forward press done by arms - it is the whole rear side compresses at the firm lead side from the ground up - just as those great ballstrikers performed:

After the trigger compression, the rear side uses the created momentum (say, as bouncing from a rubber wall) and the whole rear side takes the momentum and starts naturally to pull up, around and back creating torques in the joints from the ground up. Using the TC phase practically will leave no option for a golfer but utilizing the initially built momentum via the active rear side in the backswing. The rest is just a chain of unintentional events that everyone should dream of.

The Sagittal Plane Compression Concept. Part 4.

Even the best mechanics + conscious action is not comparable to good mechanics + untentional action, especially happening as a sequence of events where one element follows another because there is no other way. Let me take as an example pelvis area motion. There are three basic possible scenarios for pelvis movement in a rotary golf swing performed by a bipedal (not mentioning scenarios of hip sliding back and forth):
a) the rear hip goes consciously as far back as possible in the takeaway to ensure enough deep position of the rear hip to exclude the necessity of lateral shift later on in the swing (see: Clement's "Hogan" drill);
b) the lateral shift happens at the end of the backswing as one of consecutive unconscious events ensuring that the downswing is a pure rotation (see: Hogan);
c) the lateral shift happens in the downswing phase as a conscious action starting it (see: Stack&Tilt pattern).
In view what was written before, the serious advantage of the scenario b) is undoubtful.

According to my researches (not only mine, BTW - such authorities as e.g. VJ Trolio even wrote a book especially about it), Hogan's pelvis area action is one of his "secrets". His pelvis moves linearily targetwise before he completed backswing of his upper body. IMO, the trick is to be able to do it early enough so that the downswing can be a pure rotation.
Pre-secret Hogan did not perform his linear shift early enough which resulted in a necessity of mixing linear and rotational components in the motion which is easily visible on some vids. Many other differences between and after "the secret" might have been caused or at least influenced by it.

Hogan wanted to have his linear shift to happen as early as possible so that the downswing is a pure rotation while the weight is located correctly under the lead ankle. The linear shift symbolizes for a bipedal that there is no possibility of coming from the outside - while he had it 100% guaranteed what he wanted ? A rotation. An OTT move. So that he cannot hook the damned ball. He wanted a pure rotation that puts his clubhead more OTT onto the ball without any slightest possibility of slicing and power leaking - because he was so in-to-out just a second before rotation element and after linear element.
He was an unique genius.

Please watch the visualization of the SPC concept in the pelvis area:

And now a pure pleasure to see Mr.Hogan in action. Observe carefully Mr.Hogan's rear hip action. It moves linearily targetwise before he completed backswing of his upper body. It is not a conscious move - there is no time for it. It is either not a result of the deep rear hip takeaway - the hip move starts long after takeaway. It is a reaction of his pelvis to the torques that have been built thanks to creating the firm rear side sequentially from the ground up. The torques in the ankle and knee joints that cause the rear femur guide the rear hip joint the only one way - the way Mr.Hogan wanted. Observe how the ankle and knee joints release the tension (torques) just the moment the hips go linearily.
As said before, the linear part in the pelvis area must happen since humans are bipedals. The trick is to be able to do it early enough so that the downswing is a pure rotation which was one of Mr.Hogan most crucial secrets how to automate the motion and make it powerful enough independently of one's body build and individual strength.

The Sagittal Plane Compression Concept. Part 3.

Here is the general visualization of the SPC concept:

And here is the SPC concept video which is, in fact, an introduction vid to the Sagittal Plane Compression concept (SPC) that explains the optimal biomotorics of a human swinging a golf club in a macroscale. The motion that is totally free of conscious thoughts and uses the hard structure of the human body to build the sequence of events. The automatic golf swing is a dream, true, but the SPC concept can put the golfer much closer to this dream...: