Explain the importance of biomechanics in transforming our understanding of the golf swing, golf instruction and physical conditioning. 

Understanding various aspects of biomechanics is crucial to knowing why certain movements or patterns of movement are necessary features of any effective and efficient golf swing. For example, properties of our muscles such as their “force-velocity” characteristic and their ability to produce increased work when an eccentric muscle contraction is followed immediately by a concentric one determines, respectively, optimal “sequencing” or “timing” in the downswing as well as the types of movements that are most efficient and powerful. Once you understand these types of ideas, the flow on to instruction is (almost) obvious! Instruction needs to focus on the movements of the body that utilize the principles, allowing the body to “self-organize” and produce efficient movement sequences. Similarly, a person’s physical state will predicate the amplitudes of movements. That is, a person’s levels of strength, flexibility, power, control and coordination will dictate their optimal golf swing. It makes no sense, a coach asking their student to put their body into a certain position or to move it a certain way if they do not have the physical capability to do that. Flexibility is an obvious one (e.g., someone may just not be flexible enough to get a large X-Factor or coil at the top of the backswing) where the length of the muscles and tightness of the body control how much coil can be generated. Similarly, if a person does not have good single leg control (i.e., is not good at balancing on one leg), then they are unlikely to transfer weight from one leg to the other very well because they are unable to do so and at the same time maintain good balance and stability.

I first heard about practical methods of quantifying the biomechanical movements in the golf swing at the World Scientific Congress of Golf, at St Andrews in 1994, in a paper about the SportSense system. However, I understand that your thesis (originally using cameras) predates this. Please briefly discuss the background of your work and the development of the 3D system.

The first published papers investigating golf swing kinematics and kinetics appeared in the early 1980’s. My Master’s thesis and subsequent published work (Neal & Wilson, 1985) was pioneering work in 3D biomechanical analysis of the golf swing. In these early works, high speed film cameras were used to create images of the golfers from a variety of angles as they swung in a “calibrated” volume. Once the films were processed at a lab, every film frame from each camera view was projected and digitized (i.e., XY coordinates of key parts of the body were determined). These data were “combined” mathematically such that 3D coordinates of these landmarks were available for analysis. Standard mechanics principles were then used to generate the important variables required to describe the golf swing (angular and linear kinematics). This whole process of analysis took approximately 8 hours to complete (depending on the number of cameras that were used and the sophistication of the model). These days, depending on the type of system that is used, this whole process can be completed in close to real-time. Thus the efforts these days focus on making sense of the data and interpreting the information for the benefit of the coach and the player.

How has the concept moved on since those early days, and how does the magnetic field principle of the 3D system differ from the electronic and light/laser measuring principles of other biomechanical systems (SportSense, Biomeca, Taylor Made MATT system etc)?

As stated above, various systems have evolved over the last 20 years for measuring movement kinematics. These measurement systems can be basically classified into two classes: active and passive marker systems. Passive systems (VICON™, Motion Analysis Corporation™ and TaylorMade’s MATT™ system) are based around the tracking of retro-reflective (passive) markers, attached to body landmarks, by multiple (4 – 10) high speed cameras. These cameras are usually permanently mounted around a laboratory. The major benefit of such systems is that the golfer is free to move anywhere (within a calibrated volume) without any wires attached. On the down side, ‘real-time’ 3D movement analysis is not possible (post-processing would typically take approximately 20 min per swing). Further, since only the 3 translational DOF are possible with spherical markers, substantial analytics need to be performed to get true 6DOF movement kinematics. Thus, real-time biofeedback is NOT possible with such systems. Importantly for golf, passive marker systems cannot be used when direct sunlight falls on the subject.  Another weakness (overcome by using many cameras – at increased cost of course!!) is that a camera cannot see markers that are obscured by the body.  For example, if a camera is placed down the target line, any marker on the left hand side of the body could not be “seen” by this camera when the golfer is at address (or a similar body orientation).

Active marker systems (e.g., Polhemus™ & Ascension™) can be wireless or tethered and rely on actual transducers of some form inside the sensor that is attached to the body. The size of these sensors has, over the last 15 years, decreased while both their accuracy and sensitivity has improved; a result of developments in microchip technology. These systems are now capable of producing full 6-DOF 3D measurements in real-time. The greatest benefit of such systems is that they can then be used for real-time biofeedback. These systems rely on the well-known and documented physical principle that a metal object, when moved within a magnetic field, induces an electric current. Since magnetic fields are not blocked by the human body, markers can always be “seen” and the task of capturing the data is much simpler. On the down side, the best systems require that the sensors be hard-wired to the computer and large metal objects, close (<25 cm) to the magnetic field can distort the readings. Golf BioDynamics feels that these two limitations are minor tradeoff for the gains of real-time, 6DOF accurate 3D motion measurement!

Please briefly mention a few technical points about the hardware/software, including: the number of sensors; the difference between 6-degree and 3-degree standards; and the accuracy of the data, especially compared to wireless systems i.e. K-Vest, IClub.

To completely describe the movement of a rigid body in 3D space requires the measurement of both its linear movement, usually along the 3 axes of an XYZ coordinate system, as well as its orientation, often the rotations about these same axes. These six parameters (3 translations and 3 rotations) are known as the degrees of freedom (DOF) of movement. A measurement system, such as the one used by Golf BioDynamics (Polhemus) is capable of measuring all 6 DOF. Recently a number of “wireless” sensing systems have appeared on the market with their marketing materials making ambit claims about their capabilities. These types of sensors (based on the use of gyroscopes, magnetometers, accelerometers and inclinometers) do a very good job at measuring the three rotational DOF’s (i.e., the orientation of the sensor attached to the body part) but they do NOT measure the other 3DOF (the linear movement of the sensor!). What does this mean for their use in analyzing the golf swing? Simply put, you will not be able to measure any of the forward/backward, up/down and sideways movements of the body! Thus, based on the output of these types of sensors alone, you will have no insight into these VERY important features of the movement!

The accuracy of the 3DOF systems (e.g., K-vest or I-club) at measuring rotational movement is supposed to be quite good (at least according to one of the companies that makes the transducer, InterSense – www.intersense.com) with an accuracy of 1^o. We have yet to test this.  Another limitation of these sensors is that the maximum rotational speed that they are capable of measuring (accurately) is 1200 ^o/s which means that these sensors are suitable for use on the large parts of the body (e.g., hips, torso, head, legs) but not for the arm, forearm, hand and golf club where rotational speeds are higher than the rated speed of the device!

There is only one company (to my knowledge) that has a portable, wireless 6DOF tracking system that does not require large setup times and is capable of working in virtually all environments, including full sunlight. This system is produced by Polhemus Inc. (www.polhemus.com), the same company that produces the tethered version that Golf BioDynamics uses at all its locations. We have not migrated to this system for a number of reasons including, primarily, it is not accurate enough (yet), particularly when more than two sensors are being used! Once Polhemus has overcome these limitations (and if the cost is not preclusive!) we would consider migrating to this technology.

How did you arrive at the data that defines the respective acceptable ranges/‘corridors’ for each parameter? How many golfers, and of what standard, were measured to arrive at the databank on which the figures are based? 

GBD initially tested approximately 75 golfers from mostly the Australasian and European Tours measuring the 3D kinematics for each. Six of the best coaches/Teaching Professionals in Australia were asked to rank these golfers on their ball striking ability.  The averages of the top ten ranked male golfers and female golfers were used as the starting point in an optimization program that I wrote.  This optimization process had certain constraints (e.g., characteristic properties of muscles and the maximum torque a muscle can produce) and an objective function of MAXIMUM POWER, MAXIMUM CONSISTENCY and MINIMUM INJURY RISK.  Once an optimal solution was derived, a set of corridors was produced based on this solution plus and minus the average variability of the data of the ten best ball-strikers. Since then we have measured about 250 Golf Professionals from around the world and found that 75% of them fall within the corridors of our “ideal model”.  In fact, having now measured over 5000 amateur golfers crossing the entire spectrum of skill level we are assured that the better the player the closer they are to our “ideal corridors”.  These corridors are based on the fact that there must be certain fundamentals present in a quality golf swing; however, there is enough flexibility in the system to allow for individual idiosyncrasies. Recently (approximately three years ago), I modified the corridors so that they were age and sex dependent.

NEW Questions Answered:

Am I right in understanding that your Golf Swing Analysis 3D Report automatically adjusts the precise corridors for each person according to their height and weight?

No! It currently adjusts the corridors based on the age and sex of the golfer. Future versions will also include an adjustment for height, although this adjustment is relatively small – a couple of degrees and a few centimeters for some variables – not all of them!

The quantification of the various parameters of the golf swing is obviously an incredible benefit to both golfers and teaching professionals. Is it fair to say that even the best teachers cannot accurately assess the more subtle rotations when simply watching a player swing, and therefore such numerical measures are really an essential tool for teaching? Which parameters in particular are hard to spot with just the naked eye? 

This is an excellent question. Yes, even the VERY best teachers cannot accurately know, using their eyes alone or with the assistance of video, subtle but important inter-swing differences in movement as well as body orientations when the body is moving fast! We believe that the ones that are hard to spot with the naked eye include the following list

1. ‘Bending’, ‘tilting’ and ‘rotation’ of the pelvis and shoulders throughout the entire swing, but particularly at impact

2. Pelvic (Hip) ‘lifting/dropping’

3. Head ‘thrusting’ (movement towards or away from the target line)

4. Hip turn

5. The timing sequence (kinematic sequence) and timing lags of the lower body / upper body and hands

6. Body speeds – (hips, shoulders and hands)

Can you help me clearly distinguish between X-Factor and X-Factor ‘Stretch’?  My understanding is that X-Factor is the amount by which the torso rotates more than the hips on the backswing (as measured at the point of maximum hip rotation). While X-factor ‘Stretch’ is the extra rotation of the torso beyond this, ‘in transition’ i.e. in the time between the hips completing their maximum backswing rotation but before they start their downswing rotation. Can you discuss the importance of these parameters?

At every instant in time in the swing, one can calculate the angular difference between the hip and shoulder rotations. Research has shown that the size of this differential is significant at two points in the swing. The first of these is at the top of the backswing (as you correctly state, when the hips reach their maximum rotation) and is called the X-Factor (this was coined by Jim McLean back in the early 1990’s).  We usually look for an X-Factor value between 40-50 degrees.  Much less than this range can often indicate a lack of trunk rotational flexibility.  When the differential is much higher than the range it is often an indicator of excessive flexibility and an inability to ‘control’ the movement within this range i.e. lack of ‘core strength’.  This is often seen in younger developing players.

The other point is when that differential reaches its maximum – this is the X-Factor Stretch. In good golfers, this point occurs about halfway through the downswing. The sequence of movement in these players can be described as follows:

1. The hips reach their maximum rotation (top of backswing);

2. The shoulders are often still rotating (only slowly as they approach the point when they start to rotate back toward the target);

3. The hips accelerate very rapidly in the opposite direction (bump toward the target to initiate weight transfer followed by rotation), thereby increasing the angular difference between the hips and shoulders

4. The shoulders eventually begin their acceleration and decrease or close the gap between them and the hips, so that they are relatively close in terms of their rotation by impact (generally we expect that the hips are slightly more rotated than the shoulders by impact).

The X-Factor Stretch, therefore, is the amount of “lead-out” the hips gain on the shoulders in the first part of the downswing. It is calculated as the difference between the value at the top of the backswing (X-Factor) and the maximum differential between the hips and the shoulders.  For example, the average X-Factor Stretch of PGA Touring Professionals (that we have measured on our 3D System) is 16-17 degrees with the greatest measure being 27 degrees!  While this variable has a high correlation with distance, there are other important variables to consider in the ‘power equation’.  It is certainly one of the major differences seen between the playing professional and the weekend golfer!

Is it fair to say that, on the one hand, that 3D swing analysis confirms that all golfers have different swings and different areas that they need working on, with the 3D system helping Teaching Professionals to prioritise these areas.  But, on the other hand, does the 3D system also help us generalise to a certain extent by identifying certain crucial parameters that distinguish tour pros from amateurs (especially with regard to generating distance, ( X-Factor etc.)?

Yes it does. My research over the last 25 years but in particular, during the last seven years has been able to identify numerous key movement characteristics required for an effective and efficient golf swing. These include positional parameters such as a good X-Factor and X-Factor Stretch, a well-rotated body at impact, etc. Other kinematic variables such as body segment speeds (hips, shoulders and hands), acceleration and the timing of the peaks in speed are as important as the positional data but cannot be “seen” by eye (i.e., you cannot see an acceleration and you can only get a qualitative sense of speed of movement). Biomechanical analysis and description of these higher order kinematic variables has helped identify the underlying movement features that distinguish tour pros from their amateur counterparts. 3D swing analysis has definitely assisted both the player and the coach in prioritizing interventions, whether they be technical, physical or a combination of the two.

Has 3D Swing Analysis helped to dispel certain myths about the golf swing and settle arguments among golf teachers? E.g. the head does move during the swing; the hips and torso are not orientated the same at impact as at address; the hips do lead the downswing; the spine angle doesn’t remain constant during the swing.

Yes, to some degree it has and the examples that you have provided are good ones.  There are many top Teaching Professionals, Jim McLean for instance, who are strong advocates of scientific research and understand its importance in confirming their sound teaching principles.  Unfortunately the industry is still littered with those who either ignore the scientific data or are ignorant of it.  For example, an article that recently appeared in Golf Illustrated, claimed that the average golfer could drive the ball another 20 m within moments of reading the article by using their arms and hands to initiate the downswing rather than the legs and proximal body parts. This concept is flawed since the greatest amount of energy is generated by the large muscles of the body, not the small ones. Further, consistency of movement is increased when one relies on movement created by the larger muscles (e.g. torso and gluteals) as opposed to the smaller muscles (e.g. hand and wrist).  Is it worth hitting the ball a few yards further if your shot dispersion is increased!

Are their tour pros that do actually start their downswing with their upper body?

There are NO tour players whom we have measured who start their downswing with the upper body (despite what they think!). There is a big difference between feel and real! As with any population (even some of the best golfers in the world), there are outliers. Thus, some touring professionals swings may not necessarily fit perfectly into all our ideal corridors (e.g., some players keep do not have much lateral movement of their heads on the backswing; others drop their head more than is ideal on the downswing, etc.). Some players’ swings are more efficient than others and some players’ swings are “under-powered” compared to their body size and shape.  There is simply a lot of variation!

What, for you, has been the single most important thing that 3D Analysis has helped reveal about the nature of the golf swing?

The most important aspect that the 3D system has allowed us to understand is the timing or kinematic sequence of body speeds on the downswing (i.e. hips, shoulders and hands). Having these data, presented in graphical form, allows insight into the mechanical efficiency of the body’s movements as well as the overall energy and power produced during the downswing.   

What does the future hold for biomechanical swing analysis systems in golf?

Like most computer based programs I believe the evolution will be to a simpler operating system.  We hope that it will include an automated reporting system that has an ‘Artificial Intelligence’ engine capable of learning relationships amongst the data that are calculated.  For coaches and their golf athletes to take advantage of the biofeedback training capacity of the 3D system it certainly needs to be simpler than it is at the moment. Currently, a very specialized skill set is required to operate the 3D system, interpret the information (knowledge in the area of biomechanics, exercise science, computers and golf instruction at a minimum) communicate this in a manner in which is easy to understand and then implement an intervention strategy for technical change which may likely include advice on their physical make-up.

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