Analysis of Golf Swing Rob Webb
Transcript of Analysis of Golf Swing Rob Webb
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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