If one socket moved up and the other down, the resulting movement by itself would create a partial rotation centred approximately around the mid-point between the shoulder sockets. If the player stood erect, this rotation would be relatively vertical to the ground.
In Chapter Six, we noted that muscles at the side of the body can contract to pull the top of the spine to the left or right. The "spinal tilt" is the bending of the spine sideways left and right. It is also known as the lateral flexion of the spine.
This movement is the basis for our final basic putting stroke. In the stroke, the only muscles involved are those at the side of the body. They contract to pull the upper body to the left or right. The contractions cause the shoulder sockets, and ultimately the arms, wrists and putter, to move first in one direction and then the other, producing a putting stroke.
Two muscle groups are involved - a group on each side of the abdomen.
The groups are not coordinated. One group can contract independently of the other. As a consequence, there is the potential for inconsistency in the stroke.
While there is some range of side bending movement, the range is more limited than with wrists, the ball and socket shoulder joint, and the bone structure holding the shoulder socket.
Relatively large muscles on the side of the torso are involved.
The muscles move the upper body, shoulder sockets, arms, wrists and putter. The mass being moved is relatively large. As such, there is a significant momentum component to the stroke.
There is considerable movement to the eye sockets, as the top of the spine moves, causing the head and eye sockets to move. Use of the eyes to control the stroke is relatively difficult.
Theoretically, if the player stands erect with the spine vertical to the ground, the rotation plane of the stroke is vertical. If the player leans forward, the rotation plane leaves the vertical, with the top of the plane moving toward the ball and the bottom toward the body.
The rotation circle centre is somewhere between the shoulder sockets and the ball, and most likely around the abdomen/wrist area. This diagram above illustrates this point. This radius when standing erect is closer to that of the wrist stroke than other strokes. The small radius accentuates problems related to the non-vertical plane of the stroke. The problem is increased because the arms need to be at an angle to the spine. The greater the angle, the smaller the rotation circle radius. Consequently, the stroke is best performed when the arms are at a relatively small angle to the spine.
The rotation centre is steady only when the left and right contractions cause equal movements of the spine to both the left and right. Without inherent steadiness in the rotation centre, the stroke is prone to inconsistency.
The stroke is most vertical when performed standing erect. This means the eye position cannot be over the ball, as the ball will be too far away.
The side bends are limited in extent. In addition, the rotation radius is relatively small. Both factors will limit the power of the putting stroke.
There is no necessity to lean forward. In fact, the stroke is performed best without the forward lean. However, excessive side bending on, for example, long putts, could be problematic.
To get the most out of the spinal tilt stroke:
This is a simple stroke with potential for a relatively vertical swing plane and good line. However, it is intrinsically inconsistent, as it does not provide a steady eye position, nor does it allow the "eye over target" setup opportunity. In addition, it is not powerful.