The hip joints rotate under the Pure Rotation or Push and Clear scenarios. Furthermore, when they rotate, the two joints generally stay at the same level, so they remain parallel to the ground, and the axis of rotation is perpendicular to the ground.
While the two hip joints may be on the same level and generally parallel to the ground, the spinal column is tilted forward. This occurs because the knees are typically bent. The muscles around the hip joints contract to incline forward the bone structure in which the hip joints sit. When the bone structure is inclined forward, the spinal column is also inclined forward.
The angle between the upper leg and the bone structure, when seen from the side view, is 180 degrees when one stands vertically. When one goes from standing vertically, and then starts to bend the knees, the body typically reacts at the ankles by reducing the angle between the ground and the lower leg, and at the hips by tilting the spine forward at the hips and decreasing the angle between the upper leg and the bone structure/spine from 180 degrees. These movements maintain the centre of gravity over the feet and ultimately keep the body from falling forward or backward.
In the golf swing at setup, the bone structure and the spinal column which comes out of the bone structure, are tilted forward a few degrees, as shown in the picture.
Bending forward at the hips (compared to standing vertically) has a number of effects:
The picture illustrates the rotation that occurs around the shoulders when the bone structure and hips lean forward. Of particular interest is the amount of movement at the centre of the shoulders and the head. The amount of rotation at the top of the spine will be directly related to the amount of rotation of the hips. If the hips rotate in the downswing through 45 degrees, the downswing rotation at the top of the spine will be 45 degrees. If they rotate through 22 degrees, the downswing rotation will be 22 degrees.
You can get a sense of this movement by sitting in a chair, bending forward so that the spine is about 20 degrees from the vertical, and swiveling on your butt about 45 degrees in each direction from your initial position. Note how much the centre point between the shoulders and your head will move as your swivel. The centre point between your shoulders and your head will be rotating in a circle whose diameter will be determined by the distance from the centre point between the hip joints and the centre point between the shoulders, and the degree of forward tilt.
The golf swing's reaction to all this movement can vary. The simplest physical response is the "do nothing" approach, so the shoulder centre and head rotate around in a circle - away from the ball and target on the back swing, and toward the ball and target on the downswing. A more complex response is to nullify the movement by lateral side bends of the upper spine. As the rotation of the inclined spine moves the shoulder centre away from the target on the back swing, the upper spine tilts toward the target. Let us explain the spinal tilt further.
The "spinal tilt" is the bending of the spine sideways left and right. It is also known as the lateral flexion of the spine. The muscles at the side of the body contract, causing the upper spine to bend left or right, when seen from the front, relative to the lower spine.
If you lay a golf club across your shoulders, a lateral side bend will move the club from the horizontal plane to some degrees off the horizontal plane when seen from the front. The spinal tilt contrasts with the spinal twist, where the club stays on the horizontal plane.
In the golf swing, the "spinal tilt" refers to a lateral side bend toward the target on the back swing and away from the target on the downswing. Since the head sits at the top of the spine, side bending causes the head to also move toward the target on the back swing and away from the target on the downswing.
The spinal tilt is a power source, albeit a mild one, in the golf swing.
One can get a sense of lateral side bending as a power source by taking a five iron, putting a ball on a tee (to ensure a clean hit), contracting the muscles on one's lead side during the back swing and then contracting the muscles on trailing side on the downswing, all while immobilizing all other muscles. The lateral side bending will create a rocking motion that will propel the club away from the target on the back swing and then forward toward the target on the downswing, causing the ball to go forward.
You may find a bit of a challenge in hitting balls only using the spinal tilt. If you do, step away from the ball, do a number of spinal tilts to get the feel of using only the spinal tilt muscles, then retry hitting the ball. You may be able to get 10 to 20 yards distance, which would amount to one club less on iron shots.
The stick diagrams below illustrate how side bending can move the shoulders around a circle centred at the base of the spine. Because the arms and the club extend substantially beyond the base of the spine, the shoulder movement translates into a power source capable of moving the ball forward. The curved line represents the spine, bending right in the front view in the back swing (right-hander) in the left diagram, and then bending left in the downswing in the right diagram. The equal length sides of the triangle depict the arms and the top depicts the shoulders. The line at the end of the triangle depicts the club. The black circle is the ball. The arrow shows the direction of the hit. The red ball indicates the centre around which the shoulders are rotating, namely the base of the spine.
In Chapter 11, we shall see that this power source is real but small.
The spinal tilt is a golf movement highlighted by Plummer and Bennett when they introduced the "stack and tilt" golf swing. However, a number of players employ some degree of spinal tilt/lateral side bending in their swings. Most do so unconsciously. When you watch good players swing, the head and the centre of the shoulders typically stay relatively motionless, even though their bodies lean forward at setup and they rotate their hips. This occurs because lateral side bending is taking place to counteract the effect of hip rotation in combination with the forward lean.
Keeping the head relatively still during the swing makes maximum use of vision as a controlling element in the golf swing. If you think vision is not relevant, try hitting balls with your eyes closed. Because of the importance of vision, most good players keep their heads (and eyes) relatively still during the swing.
Look at swing videos of the top players. Draw a line from the head to the centre of the stance, and then watch what happens to the belt buckle. These days, the belt buckle stays on the line or moves only slightly away from the target in the back swing, but moves forward while the head remains fixed over the ball in the downswing. To a large extent, the only way to achieve this positioning is to tilt the spine through lateral side bends.
You may also be able to feel lateral side bends in your golf swing. To do this, swing slowly, and see if you can feel the muscles around your ribs on your lead side contracting during the back swing, and the muscles around the ribs on your trailing side contracting during the downswing. As a further experiment, try to keep your head in the same place over the ball in your back swing, and see if you can feel contractions on the muscles on your upper lead side. On the downswing, try to keep your head motionless and see if you can feel yourself automatically contracting the muscles on your trailing side.
Is the spinal tilt healthy? Maybe not. In most cases, tilting the spine will occur simultaneously with twisting the spine. As discussed under Spinal Anatomy, one would think intuitively that this could put undue pressure on disks, particularly when the movement is performed quickly. Some spinal tilting is likely to be okay for most people, but an exaggerated spinal tilt could be problematic, particularly when carried out without adequate warm-up, in cold weather, or with countless repetitions.
The spinal twist involves primarily the lower discs in one's back. If the spinal tilt engages primarily the upper discs in one's back, the health risks are reduced. The health risks go up when spinal tilting engages the lower discs as the same time that spinal twisting engages these same discs.
Spinal tilting and hip joint movement must be considered together, since they function interdependently. They combine to produce four options for the golf swing:
These options will be explored more fully when we look at the physics of the movements in the golf swing. At this point, the spinal tilt is presented as an option for your consideration.