Dear Chris,
Your question gets closer to the heart of the problem than just about anything! Let me clarify the issues and then discuss them.
If you use a shoulder stroke in which the triangle of arms, hands, and putter stay coordinated with the shoulder frame and the entire motion is generated and defined by the direction, amplitude, and timing of the movement of the shoulder frame (and the hands and arms have no independent movement apart from the movement given them by the shoulder frame's movement), then "the whole shebang" boils down to managing the pivot of the shoulder frame during the stroke. What is the pivot and what might happen to it during the stroke, and what can and should you do about this situation? Altogether, I call this "putting from the top."
The answer is not simply "hold the pivot still." The human body is a bit too sloppy and this stillness is only the ideal, but the sloppy reality is that the ideal is seldom what you have to deal with. The answer is to have an ideal and then to know HOW to handle the eventualities as they arise. So how is the pivot best held still? And what sorts of problems can you anticipate and how are these problem situations best handled?
IDEAL:
The ideal is to hold the pivot still throughout the stroke. The pivot is the center of mass of the shoulder frame conceived as a separate moving part of the body, albeit somewhat constrained by its connections to other body masses (head and neck, and torso and lower body, and arms and hands). The center is approximately where the clavicle bones connect each shoulder bone to top of the sternum, at the base of the neck, where the bones join in a joint (the "sternoclavicular joint") at the top of the sternum that allows a little turning in a door-knob fashion.
Moving the shoulder frame as a unit theoretically leaves the pivot undisturbed (like the axis of the door knob), simply rotating in place, whether the shoulder frame moves in a vertical plane or a tilted plane or even in a horizontal plane, so long as the movement is symmetrical about the fixed point.
REAL COMPLICATIONS:
There is some freedom in this sternoclavicular joint, but the matter is complicated by the sternum's structure and its connection to the rib cage, especially the topmost ribs.
The clavicle bones are attached to the sternum via cartilage that has a little flexibility, so moving the shoulder frame may meet a relatively fixed sternum, but there is some "give" in the way the top of the sternum and the clavicle bones are joined. But then again the top of the sternum also controls the topmost ribs, so whatever the shoulder frame does as a whole translates thru the clavicles and their junction with the sternum to move the topmost ribs at the base of the neck, and to move the lower ribs progressively less the lower you go down the ribcage. The tendency is for the head to follow the base of the neck as defined by the topmost ribs, and since these ribs connect at the back to the top of the spine, the spine in the cervical area will either flex laterally in response to the shoulder frame move or will twist in place, or some combination. This complicates the pivot stability at the top.
There is also the complication of the connection of the shoulder frame to the ribcage as a whole via the sternum and the muscles connecting the ribcage and upper torso to the lower body. In order to move the whole shoulder frame, the upper torso is moved by these muscles. Muscles on the sides in the abdomen connect the ribcage and whole thoracic cavity (as an ill-defined soft-tissue structural whole) in a spiral fashion down onto the pelvis. The external obliques wrap spirally from front on the ribcage to the back onto the pelvis while the internal obliques wrap spirally from back on the ribcage to the front of the pelvis.
External Obliques:
Internal Obliques:
Other muscles also connect the ribcage to the pelvis (e.g., quadratus lumborum):
or the ribcage to the spine in the lower back (e.g., serratus posterior inferior):
These muscles bend the upper torso laterally (side to side):
Otherwise, the top of the skeleton is connected to the lower skeleton ONLY where the spine meets the pelvic structure (a point). The tugging down of these muscles to pull the lead-side ribcage lower and closer to the lead-side pelvis is paired on the other side of the body by a muscle stretch as the rear-side shoulder rises. The shoulder naturally follows the ribcage down. There is not necessarily a one-to-one correspondence between the shoulder actions on opposite sides of the body, as some of the stretching motion on the up-side gets lost or absorbed in the soft tissue of the abdomen and the holding down of the tissue of the upwatd shoulder. The body is to a certain degree rubbery in the way the parts interact. The down action of one shoulder is not necessarily mirrored by the SAME extent of up motion of the opposite shoulder, and there is often a little lagging behind on the up side. Differential tugging down on one side not met with symmetrical and reciprocating stretching up on the other side tends to shove the body's center of gravity between the hips inside the abdomen below the navel left and right on a small curved arc. This lower COG wandering carries the whole upper torso with it. This upper-lower connection complicates the pivot stability from down below.
There is also the issue of the arms, hands, and putter. The motion of this system as part of the motion of the shoulder frame is not too much of a problem except for strokes that get outside the feet quite a ways, but even so, golfers have a tendency to move the arms and hands (and therefore the putter) independently and farther than their movement of the shoulder frame would cause the arms, hands, and putter to move. Because the arm-hand motion is always in addition to the shoulder frame action, the arms and hands tend to "flap" inward around the body in a tether-ball fashon, going back or going forward. The inertial force of this independent action tends to yank on the shoulder frame, like tugging on a seesaw seat sideways. This independent movement of the arms, hands, and putter injects forces into the motion that tend to make the pivot wander in a small arc.
Finally, there is the issue of the head. The head is typically 8% of the body mass, so a 150-pound person typically has a 12-pound head. The "head" is the skull and jaw, and this structure sits atop the spine on a joint (the "atlantoaxial joint"), and this juncture is not much lower than the bottom of the eye sockets (higher than most people assume).
The spine, joint, and head look like a bowling ball perched on a plate balanced on top of a pole.
The center of gravity of the head as a separate part is higher still, so when the head is leaned forward over the golf ball at address, the back of the neck muscles and spine stabilizing muscles hold it there. The head is then somewhat like a Tootsie-Pop being held by the bottom of the stick -- if it wags left and right, it's not too easy to control.
The question is whether the head motion drags the bottom end of the stick (the pivot) out of its still location in space. The head is like "an inverted pendulum" when it sits straight on top of the spinal column, and that is an unstable situation that is only stabilized by the structure of the joint (a plate) and the way the neck muscles "tie down" the heavy balloon of the head to the shoulder and upper torso (sort of like radio antennae guy wires) holding the head against the plate. The stability of this situation is worsened a bit when the head is tilted forward out over the torso in a putting posture, as this tips the plate and leaves all the stabilizing responsibility in the muscles and ligaments of the neck. So this challenges the pivot stability as well.
IDEAL SOLUTIONS
The way to stabilize the pivot is to fix the neck in space in the putting address posture. This works up from the neck to stabilize the head, and works down from the neck to stabilize the upper torso, while the shoulder frame motion is being made. To fix the neck in space, relate the neck to the top of theputter head and the bottom of the stroke. That is, align the line of the neck from Adams Apple or pivot up to the center of chin on the same line as the leading edge of the putter face, which should also be the midline of the center of the body and the exact bottom of the stroke arc. This is sort of like craning the neck out of your shell like a turtle and orienting the neck to match the well-aimed putter from heel to toe. Once set, maintain this line of the neck during the stroke motion. (It helps to tighten the muscles on the front / underside of the neck with the head bowed at address, as these muscles tighten the skull against the top of the spine.)
This keeps the base of the neck (the topmost ribs and the atlantoaxial joint) square to the putt line, and the base of the neck keeps the shoulder alignment square as the stroke goes forward.
Another way to use the neck to stabilize the pivot is to realize that the neck aims the face, and more particularly the nose. So aim your whole face squarely at the putter head and aim your nose in particular like a dart at a spot on the ground. If you imagine that you are Pinocchio the wooden puppet whose nose grows in length when he lies, and you've just told a whopper, and have a nose that reaches all the way to the ground, then stick the sharp tip of your nose in the ground so that any left-right forces that would waggling the head or pivot won't bother the pivot at the base of the neck.
A third solution is about the eyes, in two different ways. If you gaze straight out of the face, and face straight at the putter head, your eyes will be looking towards the ground at the sweetspot of the putter. When you focus your vision on a blade of grass immediately in front of the sweetspot, your lenses are shaped by a ring of muscles in each eye so that the shape of the lenses is just right for the distance from your eyeballs to the blade of grass to bring the image of the grass into sharp focus inside the eyeball. The farther off something is, the tighter this ring stretches the lens flat; the nearer the object is, the looser the ring muscles become and the lens fattens back out like a water balloon released from a squeeze according to its plastic "memory" (which degrades with age and so older guys need glasses to read up close -- the lenses don't puff back up fat enough like they used to when younger).
The upshot of this is that the eye muscles in focusing on the blade of grass get set for a very precise distance from eyeballs to grass, and any head bobbng up or down will make the grass blade go out of focus for a moment until the lenses adjust to the new height. Also, any head motion left or right will make the surface of the green appear to slide the opposite way a little, like someone offering you candy on a tray beneath your face but also sliding it from side to side to entice you a little extra. (There is a brain mechanism that masks your ability to notice the surface appear to slide side to side by rolling the eyeballs whenever the head slides to keep the eyeballs aimed straight at the blade of grass even though the head is moving. This is called the Vestibular-Ocular Reflex, or VOR, but you override it by allowing the earth to slide sie to side if the head moves, since you need to know this.) So loss of focus on the grass blade or sliding of the surface left-right tells you the head is moving. The pivot may still be fine, but if your aim is to fix the pivot AND hold the head still also, you need this information from the eyes. Consequently, fix the straight gaze on the blade of grass immediately in front of the putter sweetspot and get interested in looking at it and keep it in focus and still the whole time the stroke is getting done. If you are successfl, this will fix the pivot both in the up-down sense and in the left-right or front-back sense.
There is no reason not to use all three of the above solutions simultaneously.
A fourth solution involves the lower body. Widening the stance to hold the lower center of gravity still during the stroke is not all its cracked up to be.
You can widen the stance as much as you like, but this does not directly affect the forces of the upper torso shoving the hips sideways, any more than thickening the base of a tree prevents the wind from blowing the top branches about. What really matters is not just widening the stance, but also tightening the postural muscles in the lower limbs. It's a standard bit of putting lore to imagine your whole lower body set in concrete, as the tip to still the lower body. But as noted above, this does not address all the factors, and the pivot at the top can still wander about. So fixing the lower body does not by itself solve the problem, and may make other solutions harder to put into effect. You may need to keep the lower body reactive, so this solution may not serve everyone equally well.
HANDLING REAL COMPLICATIONS:
The trick here is to know what is likely to happen when the pivot moves and what to do about it to keep the stroke rolling the ball straight.
Because of the complications noted above, there are a few easy rules to help avoid problems at the outset.
First, don't use the arms and hands independently of the shoulder frame.
Second, don't move too quickly or abruptly -- the abruptness magnifies the problem.
Third, stay smooth and relaxed. Don't make a larger motion than is needed, and therefore avoid tightness and deceleration during the downstroke (as this requires a larger stroke than otherwise or else you end up short).
Fourth, have a sense of the midline of your body (a vertical lane thru the body that symmetrically divides you into equal left and right sides when you are at rest at address), and setup and move so that the actual middle of your body stays close to this imaginary fixed plane in space as established at address.
So what is likely to happen when the pivot shifts its location notwithstanding your intent and precautions? The COG in the abdomen is likely to shift back the same as the base of the neck in the backstroke, while the head's COG goes the opposite way. The hips slide to the right (rear-side) as the lead shoulder dips, while the head COG slides to the left (front-side). These two motions MAY leave the COG at the base of the neck centered, rotating in place, but it is unlikely.
My suggestion is to pay a little attention at the start of the backstroke to your hips, head, and neck pivot to see what is happening there. The best way I know to keep up with this is to watch the head-eyes especially. If the head rolls or tilts left as the backstroke goes right, the left eye will dip closer to the ground like the descending end of a seesaw of the two eyes. If this happens, you still can't be sure the pivot at the base of the neck moved, but you can sense the whole assemblage of three separate COGs in motion. Your job is to make the forward stroke have the same COG movements in a symmetrical, reciprocating way, exactly. This equal return action wll necessarily get the neck pivot back to is starting position at the bottom of the stroke, and thereafter if there is a little neck pivot sway, its hurtfuness to the straightness of the stroke should be minimized.
In the event the lower body is reacting to instability introduced by head or shoulders in motion, that is probably a restorative reaction seeking equilibrium and balance after disturbance. If you stifled this owerr-body reaction by starting out too stiff in the legs, you will feel cramped in the middle of the body, where the muscles of the abdomen are managing the stroke for size, direction, and timing. The trade-off is reacting to the pivot motion with equal reaction or keeping the legs stiff and cramping the gut and shoulder action. My choice is to stay relaxed in the lower body and let reciprocation take its course, while the stroke muscles stay relaxed to handle to size, direction and timing of the stroke.
It's better not to have any neck pivot motion, since the impact zone is a little wide and not just a single point in space. So any arcing about of the neck pivot is a problem for the straightness of the stroke. There is not really one moment when the pivot needs to be still or at least square -- there is a brief interval of time while the putter and ball are in contact and the pivot needs to remain square during this time period. In the final analysis, if the pivot comes out of position, you just need to know how to get back to the starting position during the impact zone, with least disruption to the stroke.
DRILLS
I don't really have a drill already for learning this stuff, so I'll create one. Tie something sort of weighty on the bottom of a length of string (a foot or two long) and also button the top button on your shirt. Fix the string at the top button. Then putt. If the base of the neck rotates, the string will swing under your face. Practice getting the string to swing evenly and symmetrically.
Or, hold the same string in your teeth and putt and see how it moves.
Also, get a piece of wood (a dowel rod, for exmple) as long as your arms and also get a yardstick. Stand near a wall and osition the dowel between the base of your neck and the wall level to the floor. Hold the yardstick out with hands straight to the wall and swing the ends of the yardstick like an airplane banking, and watch the dowel to keep it still on the wall.
Let me know what is going on with this for you.
RESOURCES:
Inverted Pendulum
The human body is inherently unstable
Human balancing of an inverted pendulum
Inverted Pendulum (PDF)
Improving Muscle Balance and Stability
Head and Neck Posture at the Computer
Feldenkrais Lesson of the Month Archive
Improving sports performance with Alexander Technique
Cervical Anatomy
Posture
Kinematics of Human Motion
The Biophysical Foundations of Human Movement
BioMechanics: Making sense of Balance
Vestibular System
Brain activation during maintenance of standing balance
Virtual Naval Hospital - Naval Flight Surgeon
Balance Training for Reducing Postural Sway
Posture bibliography
Posture
Elsevier.com - Equilibrium Research
Postural stability of normal subjects
Modelling the kinematics of the human shoulder
How Tiger Got Back On Track -- the obliques and the shoulders
Cheers!
Geoff Mangum
Putting Theorist and Instructor
Geoff Mangum's PuttingZone
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