Analysis of Golf Swing

Introduction

Biomechanics can be described as a scientific discipline that uses the application of

mechanical principles in order to provide an understanding of movement (Hume,

Keogh and Reid, 2005). Golf biomechanics involves applying the principles and

techniques of mechanics to a performer’s own technique in an attempt to improve

their golfing performance. Consequently, a biomechanical evaluation of performer’s

swing may incorporate qualitatative and quantitative analysis of movement, patterns

of muscle activation and the influences of internal and external forces. Researchers

have conducted biomechanical studies investigating the kinematic, kinetic and

electromyographic characteristics of the golf swing in an attempt to symbolise the

ideal golf swing, with their overall aims being to improve performance and reduce

golf related injuries, (Dillman and Lang, 1994).

Cochran and Stobbs (1968), conducted the first real pioneering study into the

biomechanics of the golf swing, they suggested that the golf swing could be

described as a planar-two link system, this system was a based on a mathematical

model which they called the ‘double pendulum’. The ‘double pendulum’ highlighted

the relationship between the pivoting motion of the left arm and the club around the

chest; they described the chest as a fixed ‘hub’. In concluding their study Cochran

and Stobbs (1968) stated that the golf swing should appear as a pendulum motion

moving through a single plain. This study was further built on by the work of

Jorgensen (1970) and Bundey and Bellow (1983). Jorgensen’s (1970) investigation

into the dynamics of the golf swing found that improvements could be made to the

‘double pendulum’ model if movement of the chest (‘hub’) was incorporated. The

study posited that by allowing both vertical and horizontal acceleration of the chest

superior upper body rotation could be achieved which in turn allowed for greater club

head speed to be generated. Bundey and Bellow (1983) suggested that the actions

of the upper body and the arms during both the downswing and the backswing were

conducted in a single plain. They also highlighted the wrist action during the

downward phase of the swing, stating that the cocking and uncocking action of the

wrists as well as torso rotation was crucial in order to achieve maximum club head

velocity.

The general consensus amongst the previous research was that all the movements

carried out during backswing and the downswing phases the golf swing were through

a single plain. These studies all used similar models of varying levels of complexity

in which to perform kinetic analysis of the golf swing. However, with technological

advancements in the equipment used to analyse the golf swing, recent literature has

called into question the validity of these studies, suggesting that the models used

were limited and the golf swing could be better described as a three dimensional

model. Nesbitt and Serrano (2005) proposed that models used by Jorgensen (1970)

and Bundey and Bellow (1983) were restricted to one or two rigid link (double

pendulum) systems which constrained the motions to two dimensions.

Nesbit (2005) conducted a three dimensional kinematic and kinetic study analysing

and comparing the golf swings of 84 males and one female all of whom were

amateur players of various skill levels. The analysis was achieved by using a

variable full-body computer model of a human, combined with a flexible model of a

golf club. The results from the analysis revealed that the golf swing is a highly

coordinated and individual motion where significant subject-to-subject swing

variations exist. The analysis also found that as the club moved through the stages

of the swing it did not appear in one constant plane. This is supported by the work of

Egret et al., (2003) and Coleman and Rankin (2005). Egret et al., (2003) conducted a

three dimensional kinematic analysis of three different clubs during the golf swing

and found that there was evidence to suggest that certain clubs followed different

swing planes. Coleman and Rankin (2005) findings stated that the left arm and the

shoulder girdle do not move in a consistent plane throughout downswing and

therefore previous models of the downswing in golf may be inaccurate.

From reviewing the literature above, it is clear that there are inconsistent findings, so

for a greater understanding of the complex process that is the golf swing to be

obtained a structured analysis of the four different phases of the golf swing needs to

be used in order to provide accurate and understandable feedback. Completing a

quantitative analysis of a performer’s downswing and qualitative analysis of their

stance, backswing, downswing and follow through and making comparisons against

what literature describes as the ‘ideal’ swing will enable this to be achieved. Breaking

down a skill into a series of phases allows both coaches and athletes to identify what

is causing certain errors (Carr, 1997).

Method/Filming Process

Subject. The subject (age, 21 years; height, 178cm; weight, 75kg) an amateur golfer

gave their voluntary and informed consent to participate in the swing analysis, which

was approved by Loughborough College.

Recording of the swing. The video camera (Sony Handycam, model HDR-FX1000)

was mounted on a stationary, rigid tripod following the frontal plane of motion. It was

positioned 5 metres back from the action point in order to reduce the levels of

perspective error. The lens was adjusted to focus the image of the subject; this was

achieved by zooming in on the subject and then zooming out to the required field of

view. The field of view was adjusted to coincide with the area where the subject was

performing the swing. This maximized the size of the subject on the projected image

and allowed for increased accuracy during the digitising process. The camera was

set with a shutter speed of 1/1000 seconds to insure for a sharp image and sufficient

light was directed onto the subject by using three mounted floodlights. One was

positioned near the optical axis of the camera and the other two were situated either

side of the plane of motion at a 30° angle. The subject being analysed wore dark,

close fitting clothes and prior to the start of the filming process joint makers were

placed at the centre of rotation on the subject’s left shoulder joint and left wrist, a

marker was also placed on the club-head. This was so the centre of rotation for each

joint could easily be established for each frame during the digitising process. The

subject was instructed to stand perpendicular to the axis of the camera in order for

the whole swing to be captured. On the camera operators cue the subject performed

a golf swing, hitting the ball perpendicular to the axis of the camera. This filming

process was repeated three times.

Data Collection. The best of the subject’s three swings was chosen. The selected

video clip was then played through a computer software package called Silicon

Coach to create the subject’s swing pattern using the double lever model. This clip

was advanced frame-by-frame until the subject had completed their backswing. On

the initiation of the subject’s downswing the digitising process was started by locating

and clicking on the joint markers positioned on the subjects left shoulder, left wrist

and the club-head. The film was then advanced frame by frame with the process of

clicking on the left shoulder, left wrist and club head being continually repeated until

the end of the swing. The fully digitised image was then printed off.

Qualitatative Analysis. Using the print out of the swing pattern and the video clip, the

subject’s swing was qualitatively analysed. The clip was reviewed in order for

subjective feedback to be provided on the four phases of the subject’s golf swing. In

addition to this, the subject’s swing pattern was visually compared to a swing pattern

of a professional (also derived using the double lever model) and an analysis of the

subject’s timing and technique were made relative to that of the professional’s.

Quantitative analysis. In order to provide objective feedback on the subject’s

downswing, the arm and club angles were measured from the digitised image. The

arm angle is illustrated as in figure 1 and the club angle (angle between the axis of

the arm and the axis of the club) is illustrated as in figure 1. Both the arm and the

club-head angles were measured for every digitised frame using a protractor. When

recording the angles of the arm and the club if the distal part of the arm was down

(hand below shoulder) then the angle was 0°. Any clockwise angle from this point

was recorded as a positive angle and any anticlockwise as a negative.

Figure 1. Determination of the arm and club angles for golf swing analysis.

Results

Frame Number Time (s) Relative Club

Angle

Absolute Arm

Angle

1 -0.76 -127 -142

2 -0.72 -125 -142

3 -0.68 -122 -139

4 -0.64 -120 -138

5 -0.6 -119 -136

6 -0.56 -107 -135

7 -0.52 -100 -132

8 -0.48 -99 -128

9 -0.44 -94 -119

10 -0.4 -89 -112

11 -0.36 -84 -109

12 -0.32 -75 -103

13 -0.28 -73 -94

14 -0.24 -67 -86

15 -0.2 -54 -72

16 -0.16 -48 -68

17 -0.12 -43 -61

18 -0.08 -37 -32

19 -0.04 -24 -12

20 0 -4 -2

21 0.04 12 8

22 0.08 27 14

23 0.12 32 25

24 0.16 41 37

25 0.2 63 45

26 0.24 74 51

27 0.32 84 62

28 0.36 84 70

Table 1. The subject’s relative club and arm angles measured from the digitised

image.

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4

-150

-100

-50

0

50

100Relative club angle Polynomial (Relative club angle)

Angle (Degrees)

Tim

e (

se

co

nd

s)

Figure 2. Graph representing the relationship between the relative club angle and

absolute arm angle during the downswing.

Figure 3. Changes in position and speed during the golf swing of a professional.

Adapted from Budney and Bellow, 1979 and copied from Hay, 1993.

Table 2. Phase analysis model, providing a qualitatative analysis the four different phases of the subject’ swing.

Phase Description Stance Backswing Downswing Follow-throughSub-phase 1 Feet facing forwards

shoulder width apart

allowing for good

stability, with eyes on

top of the ball.

Head is kept still and in

an appropriate position.

Little weight transfer

onto the front foot

caused by lack upper

body and trunk rotation.

Good extension of the

arms through and past

impact.

Sub- phase 2 The right shoulder is

slightly lower than left

shoulder suggesting that

more weight placed on

his back foot.

No vertical or horizontal

acceleration of the ‘hub’

(chest) is present and

there is a slight bend in

the left arm at the top of

the backswing

suggesting that he may

be over swinging.

Wrists are cocked at the

point of impact reducing

the risk of a hook or a

slice.

Head remains in an

appropriate position for

the duration of the follow

through.

Sub-phase 3 Knees are only slightly

flexed.

There is a lack of flexion

in the knees which is

limiting weight transfer

onto the back foot,

negatively affecting the

power of the swing.

Maintains an

appropriate head

position throughout the

downswing and the

arms were fully

extended on impact.

Suitable flexion of the

back knee allows for

rotation of the body.

Figure 4. Digitised images comparing the subject’s swing pattern to that of a

professional. The swing pattern of the professional is taken from William (1969) and

the professional is Bobby Jones. The subject’s swing pattern was created using the

Silicon Coach software.

Discussion

Qualitative analysis is a systematic observation and introspective judgement of the

quality of human movement its purpose is to provide the most suitable intervention in

order to improve performance, (Knudsen and Morrison, 1996). Qualitatative analysis

was completed using video playback to provide subjective feedback on the four

phases subjects swing (table.2). As well as this, a subjective comparison of the

subject’s downswing swing to that of a professional golfer was also completed

(figure.4).

Stance (Set-up)

The subject’s stance was reasonable good. Their shoulders and feet were parallel.

Their feet were wide enough to allow for good stability and the right shoulder was

slightly lower than left shoulder suggesting that slightly more weight was placed on

their back foot. 50-60% of the golfer’ weight should be on the back foot (Barrentine et

al., 1994). However, there was very little flexion of the knees present, which if

maintained in other phases of the swing could inhibit weight transfer, consequently

reducing both swing power and control. A set-up with knees flexed to 20-25° is

thought to be most favourable for generating optimal power and maintaining control

of the golf swing, (Hume, et al., 2006).

Backswing

During the subject’s backswing there is an evident lack of vertical and horizontal

acceleration of the ‘hub’ (chest). Vertical and horizontal acceleration of the ‘hub’ is

central in order to produce greater levels of upper body rotation, which can create

increased club-head speed. By allowing both vertical and horizontal acceleration of

the chest, superior upper body rotation can be achieved, which generates greater

club head speed (Jorgensen, 1970).

A lack of flexion in the knees was also apparent during the subject’s downswing.

This lack of flexion limited their ability to transfer their weight onto their back foot;

consequently having a negative effect on the velocity of the club-head at impact. For

club head velocity to be maximised at impact, considerable ground reaction forces

(Newton’s 3rd law) must be produced (Richards et al., 1985). In order to increase

ground force reactions the legs should be pushed down into the ground.

Subsequently, an apparent lack of flexion in the subject’s back knee suggests a lack

of ground force reaction on the subject’s back leg during the backswing. When

investigating the differences in magnitude of the transfer of weight between golfers of

varying ability Kawashima et al., (1999) reported that during the backswing low-

handicap players had considerably greater GRF on the back leg than higher

handicappers.

Downswing

The main purpose of the downswing is to return the club-head to the ball in the

correct plane with maximum velocity (Hume et al., 2005). During the subject’s

downswing there is little weight transfer onto the front foot caused by a lack of upper

body and trunk rotation. As a result, a lack of club-head acceleration is present

during the subject’s downswing. This corresponds with Newton’s second law, which

states that the acceleration of an object is proportional to a force being exerted on an

object. Applying this theory to the subject’s downswing there is lack of force being

exerted as result of poor upper body and trunk rotation.

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