Traditionally, dynamic balance or weight transfer was the coaching term used to describe how the body’s mass is moved during the swing (Leadbetter, 1990, Mann, 1998). It is also described as the pivot (Leadbetter, 1990, McClean, 1996) the appropriate rotating transfer of weight from its original static position at address to the trail side in the backswing back onto the lead side during the downswing and follow through (Hellstrom, 2009, Hogan, 1985, Leadbetter, 1990, McClean, 1996)
The importance of weight transfer and better golf swing performance has been emphasised in coaching (McMaster, 2009) and scientific literature (Hume, 2005) with consistent links regarding weight transfer, as indicated by centre of pressure movement (McGhie, 2014) correlated with clubhead speed (Ball, K., & Best, R. 2012, Chu, et al, 2010)
Mackenzie suggests that the concept of weight shift was an ambiguous mix of centre of mass motion and foot pressure but with the use of pressure and force-recording devices to quantify a golfer’s interaction with the ground becoming commonplace among golf instructors, the terms ‘pressure shift’ and ‘weight shift’ are now clearly delineated in most popular golf instructor education platforms. (Routledge International Handbook of Golf Science p.1)
Centre of mass and Centre of Pressure
The golfers centre of mass also known as centre of gravity is typically located slightly above the navel in males who are standing upright and slightly below for females. The centre of mass is not a fixed location, it is a point in the body around which its weight is balanced.
The centre of pressure is the average location of the vertical force applied by the golfer’s feet on the ground. When a person is standing still the centre of mass would line up directly above the centre of pressure. For the remainder of the paper centre of mass and centre of pressure will be referred to as COM & COP.
Figure 1 is a face on view of a right handed golfer that illustrates the relationship between COM and COP during a full golf swing. The centre of mass is shown by a blue ball in the middle of the golfer, the two blue arrows are lead and trail foot force and the centre of pressure is located at the base of the yellow combined ground reaction force arrow. The force arrows are scaled so they show magnitude and direction of the force applied by the golfer’s feet.
- At address the golfers COM is directly above their COP.
- During the backswing, the golfer rotates their torso around their spine and shifts pressure to the trail right foot. Their centre of mass has shifted away from the target, partly caused by the mass of the pelvis and torso moving away from the target but also because the golfer is moving their arms to the side as well. The COM has stayed within the COP.
- From the top of the backswing the golfer makes a horizontal push so we see the combined GRF arrow tilt substantially towards the target. This quick sideways push starts the body moving towards the target during the downswing.
- The centre of mass moves as the thighs, pelvis and torso are moving towards the target but the golfer does not want to move too much so a large lead leg vertical push is visible tilting the combined GRF arrow away from the target.
- This is an important feature of good players as it creates dynamic stability, helps resist the centrifugal pulling forces of the club, helps the rotation of the body and increases parametric acceleration at impact.
- The golfer continues to pivot their torso around their spine through impact while applying both pressure and mass into the lead foot
- During the downswing the golfer is pushing against the ground anterior/posteriorly, laterally/medially and vertically, without the ability to produce this torque at the feet the golfer would lose control over both the magnitude and the direction of hip rotation which is instrumental in maximising transfer of force to the club through the sequential link and delivering the clubface square to the target at impact.
- The golfer completes the golf swing in balance.
Dynamic balance influences both distance and direction. It can alter the swing path, the length of the swing arc and the bottom of the swing arc, it also affects the swing principles of timing, release, swing centre and impact.
As nearly all good golfers shift their pressure into their trail leg in the backswing and pivot correctly to produce optimal impact conditions, a reverse pivot is described as the complete opposite, both pressure and mass moving onto the lead side then either shifting to the trail side during the downswing or remaining on the lead side throughout the whole swing. This results in a lack of power and the inability to create a consistent strike on the golf ball.
When the golfer moves their weight and pressure to the trail leg on the downswing (figure 2) it alters the spine angle created at address and shifts the swing centre behind the ball changing the low point of the swing arc producing a shallow attack angle, decreased shaft lean, increased dynamic loft and possibly a ball contact that is low on the clubface.
If the ball is struck in line with the clubhead’s centre of gravity the resulting trajectory will be one that is higher than normal but with decreased ball speed and distance.
Striking the golf ball below an iron clubhead’s centre of gravity will produce a trajectory that is lower than normal. A low face contact on a driver will produce an initial trajectory that is lower than normal but with an increase in backspin rate due to gear effect.
The angle of attack also plays a significant role in determining the club path which could be out-in. A club face that is open to the swing path but closed to the target line will produce a fade ball flight.
A slide is defined as any excessive lateral movement towards the target (figure 3) throughout the downswing. During a slide the golfers mass travels towards the outside of the lead foot which will steepen the angle of attack, increase shaft lean, decrease dynamic loft, cause a trajectory that is lower than normal and produce a swing path that is in-out.
If the clubface is at right angles to the swing path the resulting shot will be a push. A clubface that is closed to the swing path but open to the target line will result in a draw, open to both the target line and path, a push slice and if the clubface is closed to the path and target the resulting ball flight will be a pull hook.
A slide will also decrease clubhead speed therefore decrease distance.
The shape the clubhead makes as it swings around the golfer is technically an ellipse but may be viewed as a circle. At the centre of the circle is the swing centre also referred to as the centre-hub (Cochran & Stobbs, 2005), it is a point located on the thoracic spine – T11 vertebrae (Ferrell, 2017) where the torso pivots around the axis of the spine (Hellstrom, 2009) and a point where which the hands will be swung in a circular arc around (Cochran & Stobbs, 2005). It is greatly influenced by the angle of the spine created at address (Cochran & Stobbs, 2005).
The average golfer forward bends 15˚ at set-up and trail side bends 14˚ as the trail hand is lower on the golf club. During the backswing the golfer rotates their torso 90˚ around their spine and extends by 15˚ but replaces extension with 24˚ of lead side bend which allows the golfer to maintain posture, a centred pivot and a healthy relationship of mass to pressure enabling proper pressure direction in the downswing.
During the golf swing the torso doesn’t move much laterally or vertically, the body rotates and changes angles, but laterally the upper body moves very little, 1-2 inches in the backswing
A Sway is defined as any excessive lower body lateral movement or upper body lateral movement away from the target during the backswing. It forces mass and pressure to the outside of the trail foot and shifts the swing centre making it very difficult to develop a proper weight shift during transition and the downswing.