When analysing the golf drive biomechanically the swing can
be broken down into five distinct phases. These phases include: the address,
back swing, top of back swing and beginning of down swing, downswing and contact
and follow through.
Address
The address refers to the static position the golfer is in before
they play the shot, optimal biomechanical positioning should align the golfer
to the target, establish dynamic and static balance and provide the optimal
shaft angel and grip on the club. In preparation
for the dynamic movement of the swing the golfer’s legs should be slightly bent
and pushed firmly into the ground, preparing to counter act the ground reaction
force and Newtons third law of equal and opposite reaction.  |
| Figure 1. Optimal address |
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| Figure 2. Reverse k stance |
Back Swing
The
golf swing consists of 3 parallel points pivotal to both force creation and
accuracy, these include: parallel point 1, consisting of the club shaft being
parallel to the ground at the beginning of the back swing (figure 3), parallel
point 2, when the front arm is parallel to the ground (figure 4) and parallel
point 3 related to parallel point 1 but on the downswing. The primary role of
the back swing is to provide a base link for the kinetic chain and to prepare
the muscles for force preduction in the downswing. ( Hume, Keogh, & Reid, 2005) As the golfer
begins to rotate in the back swing torque, defined as Force X distance is
delivered in an up down process. (Blazevich,
2007)
From the commencement of the back swing through to parallel point 1 a one piece
take away is considered optimal. As seen in figure 5 a one piece take away
refers to maintaining the triangle formed by the two arms and the chest
through to the end of the takeaway period at parallel point 1. Chua, Sella, & Lepha, 2010 found that the delayed release of the club and increased
back swing angle created from the one piece takeaway increased torque applied at
the mid-point of the shoulders resulting in improved club rotation and an
increase in club head velocity. As mentioned in the address phase, the reverse k stance
allows the golfers weight to shifted laterally onto to the back foot as the
range of hip rotation is increased as the left hip turns the pelvis away from
the target resulting in the arc of the swing being flattened. (Maddalozzo,
1987)
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| Figure 3. Parallel point 1 |
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| Figure 4. One piece take away |
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| Figure 5. Parallel point 2 |
Top of back swing and
beginning of down swing
In terms of force production the top of the back swing and
the beginning of the downswing is the most crucial point of the golf swing,
through a point known in golf as the X factor. The X factor refers to the
maximisation of the hip and shoulder angle, resulting in increased rotational
velocity and increased club head speed. Figure 6 outlines the correlation between
x factor stretch (shoulder rotation - hip rotation) and swing speed, reviling
that golfers should focus on creating separation between backward rotation of
the upper torso and pelvis. (Chua, Sella, & Lepha, 2010) In addition to
shoulder rotation research has reviled the benefit of left knee flexion for
right handed golfers at the top of the back swing, with results indicating that
for every one standard deviation increase in leading knee flexion angle, ball
velocity increased 0.203 standard deviations. (Chua, Sella, & Lepha, 2010) In order to maximise
distance at this stage of the swing considerable ground reaction forces should
be produced as the body weight is transferred from the back foot to the front
during the downswing. Optimal performance results in the effective utilisation
of momentum generated by bodily movements during the golf swing. ( Hume, Keogh,
& Reid, 2005)
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| Figure 6. X factor stretch |
Downswing
The purpose of the downswing is to return the club head
through the slot angle at the maximum velocity. Preceding the X factor the golfer
vigorously releases and rotates forward, as the body weight is shifted to the
leading foot, bringing the club head to the ball in 0.30 to 0.06 tenths
of a second. Figure 7 highlights
the slot angle created from the position of the shaft at address and the
position of the shaft at parallel point 2, figure 8 demonstrates the optimal
downswing through the centre of the slot angle. As the golf swing is a throw
like movement the kinetic chain in the downswing works sequentially in a bottom
up process as the swing progresses
from the legs, through the hips, lower back, upper back, shoulders, arms, and
then wrists. ( Nesbit & Serrano, 2005) When performed
optimally summation of forces is in play as the amount of kinetic energy
is greater than the sum of the parts. ( Hume, Keogh, & Reid, 2005) As the club travels from parallel point 3
to impact and the wrists unlock, the torque components rapidly decrease as the
wrists cannot keep up with the rotational speed of the club at contact,
resulting in all torque components working negatively. It is at this point that
the wrists transition into a free hinge arrangement as the golfer simply holds
on to the club as its momentum carries it to impact. In an example of Newtons 3rd
law, as the wrists begin to work negatively the straightening of the shaft
continues to accelerate the club head resulting in club head velocity peaking precisely
at impact. ( Nesbit & Serrano, 2005)
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| Figure 7. Slot angle |
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| Figure 8. Downswing through the slot angle |
Contact and follow
through
As the club comes through the slot angle during the
downswing not just velocity is important but also club face angle leading into contact.
As Newton's laws of motion predict during the golf swing significant
correlations are apparent between club head speed and total work, with total
work being classified as the ability to apply forces and torques in the
direction of motion during the downswing. Optimal performance results in higher
total work and the point of impact. As mentioned in the down swing it’s at this
time that arms take over from the wrists, pulling inwards and decreasing the
distance from the club to the upper torso, increasing acceleration (figure 9). (Hellstrom,
2009)
During impact the club face and the ball produces torque that can twist the
club face if the sweet spot of the club doesn’t make contact with the ball,
resulting in the ball loosing accuracy. When driving off the tee the golfer can
take advantage of moment of inertia, to counter act the torque of the contact.
Moment of inertia refers to the resistance an object has to torque. (Blazevich, 2007) In order to
eliminate excess torque golfers need to strike the ball where the moment of
inertia is largest, referred to as the sweet spot. After contact is made with
the ball and Newtons Third Law has occurred the golfer continues on the designated
swing path as the body decelerates the club head by using eccentric muscle
actions. The golfer should finish in a balanced position with the trunk facing
the target with the hips and left angle rotating to absorb the weight transferal.
( Hume, Keogh, & Reid, 2005)
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| Figure 9. Decrease of club distance |
Looking at Newtons Second Law: ‘the acceleration of an
object is proportional to the net force acting on it and inversely proportional
to the mass of the object’. (Blazevich, 2007) Using the club speed produced during the
previous phases of the swing, the subsequent ball speed and impact time of the
club on the ball can be used to work out the acceleration and force required to
move the ball at that speed.
F= ma
Change in acceleration
/ collision time = ball acceleration X the mass of the ball
For the sake of these calculations the ball will be taking
off at 283kph or 78.7 metres per second, approximately 1 and a half times the
club speed at impact with a contact time of 0.0005 seconds and golf ball mass of
.0459kg.
78.7 m/s / .0005
= 157,400 m/s/s
157,400 X .0459
= 7224.66n or 736.710kg
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