Spine rotation

As a hugely significant segment both anatomically and within the golf swing, understanding healthy spine movement is vital for multiple reasons such as pain avoidance, force production/application as well as areas including club delivery as for some, how the spine moves will be critical in helping control and influence how the club is delivered through impact. Over the next four articles, we’ll discuss what is healthy spine movement in golf as well as explore common patterns of spine dysfunction often seen in golf and possible influences behind such movements.

How the spine is defined and measured in 3D.

Before we discuss spine movement in golf, it is important to recognise and understand how spine values are both produced and calculated with most 3D motion capture systems. Many commercial systems use single segment sensors to produce spine values, now although this does provide a global value of how the segment that the sensor is attached to is moving, this method is simply not accurate to produce actual spine values as there are 24 main vertebrae in the spine therefore to measure and track exactly the patterns the spine moves through with one sensor is simply not achievable. Also of vital importance is the mathematical model used to calculate the values, perhaps a better question to ask of any 3D motion tracking system is not to ask what is does capture, ask what it doesn’t capture and how does it give spine movement from only one sensor? Therefore, in the Bull3D system, these patterns are called pelvis thorax interaction as this is a much more accurate definition relative to the sensor numbers available than spine rotation as to accurately produce spine values requires a sensor on each individual vertebra and some very complex mathematical modelling. However, from the three orientation values the thorax and pelvis produce in the Bull3D system, we are able to accurately predict spine movement from the global movements produced by these two segments by relating once to the other, although of much more significant influence is the understanding and knowledge the end user has both of the biomechanics of the spine as well as the anatomical considerations behind spine movement. These articles will look to enhance and develop this knowledge allowing for more accurate reading of the plots and greater understanding of what the plots are reflecting.

Spine rotation in the swing.

For clarity, in this article we will purely be discussing healthy anatomical spine movement, therefore where as in previous articles we have explored the influences behind many movements, such as concept, schema, constraints etc. this article is dedicated simply to how the spine is moving anatomically. Also, the next three articles in this series on spine movement will look at typical dysfunctional patterns therefore these will not be acknowledged in this article, however they will be discussed at length in the next editions. Also, in the future articles we will acknowledge and share other influences behind spine movement such as lower limb function as well as the movements produced around the neck (cervical spine) as this article is directed purely towards the contribution provided by the ribcage and pelvis.

For the spine to rotate, it moves through three dominant rotational patterns – rotation (rotation around the Z axis), lateral flexion (rotation around the Y axis) and flexion/extension (rotation around the X axis). To provide a very short and extremely brief review, when humans are standing upright and in good anatomical posture (spine has maintained its three natural curves – cervical, thoracic and lumbar) for the spine to rotate it moves essentially through rotation, however as soon as the human moves into their start position, two significant changes occurs, firstly the muscular activity through the paraspinals (the muscles that run up both sides of the spine) increase as this is the bodies way of preventing gravity for pulling us down and secondly, because there are elements of flexion across the three main spinal segments, this changes the mechanical position the vertebrae can move from and the ranges they can now move through. A short and crude way of experiencing this, stand upright with your arms folded across your ribcage, rotate both clockwise and anti- clockwise and reference how far you can rotate. Now, with your arms still folded across your ribcage, bend from your hip joints as far forwards as you are able and then repeat the rotation, reference how far you can rotate compared to when standing upright, it should be considerably less. Therefore, when in the start position in golf, due to the changes in muscular activity and vertebrae position compared to upright standing, to achieve rotation as coaches would colloquially describe requires a very different spine movement than if the golfer was standing completely upright. In the Bull3D system, the plots are produced by the numerical differences between the relative orientations of the pelvis and thorax (ribcage), for example if the ribcage is rotated 10° open and the ribcage is 5° open, the spine (pelvis thorax interaction) will return and display a value of 5° open as the values are the thorax orientation relative to the pelvis.

Start

At set up, due to the task demands of golf, the spine is placed into two evident orientations, (for right handed golfer) lateral flexion to the right and flexion. Flexion in our world and definition is being defined by the ribcage being further forwards (flexed) than the pelvis, therefore due to the numerical difference this place the spine in flexion, lateral flexion being the ribcage is more laterally flexed to the right than the pelvis.

Backswing

Throughout the backswing, to achieve rotation as referred to by coaches, the spine moves through two predominant patterns, left lateral flexion and extension. These two movements combined help produce rotation. In the graph below, you will see how through the backswing phase (A-T), the spine is moving through left lateral flexion (grey plot) and extension (green plot), combined they help produce and provide the rotation which is shown by the blue plot. Two of the main areas of interest when looking as these two movements are the shape of both plots, essentially, they follow and track similar patterns and secondly, although the spine is extending is does not actually achieve and move into extension, this is seen and reflected by the green plot not moving below the horizontal zero line, therefore to reinforce, the spine starts in flexion, it extends as it rotates however it does not move into extension.

Downswing

During the downswing, you will observe how the three plots once more follow a similar shape, also at a similar rate, with the slight exception at mid-point in downswing where the blue plot (rotation) shows the pelvis is rotating anti clockwise more than the ribcage. On impact, again with the slight exception of the blue plot, the grey and green plots have returned to similar (not exact) values produced at start. Typical external influences for the slight change in spine shape are the weight of the club which can increase up to 95 kg on impact due to the influence of gravity and centrifugal/centripetal force leading to small deformations in the spine. Even for the most robust and durable humans the spine will still deform slightly due to the extreme forces both internally and externally the spine is being subjected to.

Post impact to finish

Post impact, asides from the rotational plot as at this point for many, the pelvis and ribcage are now rotating at a similar rate, the descent in the grey and green plots are closely matched reflecting equal amounts of extension and lateral flexion (returning close to upright) as the golfer approaches the end of the through swing.

Summary

This short article is designed to accomplish and achieve one main objective, to provide a reference to relate to when looking at the spine data (pelvis thorax interaction) of what healthy spine movement looks like in plot format. Over the next three articles in this series, as mentioned earlier I will share common dysfunctional patterns and the typical influences behind these movements. Attached to this article is a good example of spine/ribcage movement in animation format as this will hopefully provide a good visual reference of how the ribcage moves when the spine is anatomically functioning well.