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Golf Science

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This chapter aims to provide an overview of some of the key issues and developments in golf science over the last few years - essentially by reviewing some papers leading up to the last World Scientific Congress of Golf (2002) and others subsequent to the publication by Farrally et al (2003) on golf science at the beginning of the 21st century. As such, it is recognised that the material presented is by no means inclusive of all worthwhile golf research during this time period, rather it is intended to reflect on the main research domains in golf performance of the authors, namely biomechanics and performance measures, psychology, and technology. Cochran (2002) stated that whilst the benefit of high-tech equipment based on genuine science is real, it is nonetheless small. Anecdotally, golfers often report greater performance benefits than testing and theory suggest, supporting the self-efficacy brought to the game by technologically advanced equipment. Furthermore, enhanced teaching, improved fitness and course maintenance have all contributed to improved performances in the game.
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Golf Science
Eric Wallace, Sport and Exercise Sciences Research Institute,
University of Ulster, Newtownabbey, Co Antrim BT37 0QB.
Kieran Kingston, Cardiff School of Sport, University of Wales
Institute Cardiff, Cardiff CF236XD.
Martin Strangwood, Sports Materials Research Group, Department of
Metallurgy and Materials, University of Birmingham, Edgbaston
Birmingham, B15 2TT.
Ian Kenny, Biomechanics Research Unit, Physical Education & Sport
Sciences Department, University of Limerick, Ireland.
1.1 INTRODUCTION
This chapter aims to provide an overview of some of the key issues and
developments in golf science over the last few years - essentially by reviewing some
papers leading up to the last World Scientific Congress of Golf (2002) and others
subsequent to the publication by Farrally et al (2003) on golf science at the
beginning of the 21st century. As such, it is recognised that the material presented is
by no means inclusive of all worthwhile golf research during this time period, rather
it is intended to reflect on the main research domains in golf performance of the
authors, namely biomechanics and performance measures, psychology, and
technology. Cochran (2002) stated that whilst the benefit of high-tech equipment
based on genuine science is real, it is nonetheless small. Anecdotally, golfers often
report greater performance benefits than testing and theory suggest, supporting the
self-efficacy brought to the game by technologically advanced equipment.
Furthermore, enhanced teaching, improved fitness and course maintenance have all
contributed to improved performances in the game.
1.2 GOLF BIOMECHANICS AND PERFORMANCE MEASURES
Farrally et al (2003) indicated that the four world congresses to date had attracted
considerable biomechanical research (with 29 studies reported in total in the
Proceedings of the WSCG), yet they claimed that understanding of the golfer’s
interaction with the club was still too crude to fit clubs properly and we were still a
long way from understanding the complex movement pattern of the golf swing. The
biomechanics of the golf swing has remained a popular area of study, with a number
of research publications appearing in a range of journals and refereed conference
proceedings. A comprehensive review article on the role of biomechanics in
maximising distance and accuracy of golf shots has since been published (Hume et
al. 2005) Experimental work involving single-subject and group designs has also
been published, as well as mathematical and computer modelling studies. There has
been considerable interest in the traditional areas of kinematics and kinetics of the
golf swing, for a range of players of varying ability, but with little consideration of
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the female golfer. The mechanisms by which players generate high club head
velocity have also been further investigated, along with a number of studies on
putting techniques and putting devices. The utilisation of high specification launch
monitors has permitted investigations into player/ equipment interactions and
performance measures, while biomechanical analysis methods of the swing and the
nature of swing planes have also received attention. Biomechanical analysis of the
golf swing has sought to characterise swing patterns for elite and non-elite golfers,
and more recently, describe the interaction between the golfer and club.
The descriptive kinematic analysis of shoulder motion during the swing by
Mitchell et al. (2003) provided a baseline reference on the range of motion of the
shoulders for college, middle-aged and senior golfers. Senior golfers were observed
to demonstrate 38º less rotation and 18 º more right arm abduction at the top of the
backswing compared to college golfers. Wallace et al. (2004) examined the effects
of long drivers on selected body kinematics and temporal aspects of the golf swing,
and found no driver length effects on transverse hip rotation at key positions during
the swing, but significant effects on shoulder rotation at impact. Longer club length
resulted in an increase in overall swing duration, yet the temporal phasing of the
backswing and downswing components was unaffected. In one of the few studies to
include an examination of female golf swings, Egret et al. (2006) observed females
had wide swings with larger hip and shoulder rotations at the top of the backswing
compared to men, and concluded that two kinematic patterns existed yet there were
no significant differences in club head speed between the male and female golfers.
An important methodological paper by Wheat et al. (2007) showed that thorax
alignment using Cardan angles would not be affected by out-of-plane motion,
whereas transverse plane alignment of the upper body calculated using the inter-
acromium vector (commonly used in many previous studies) while valid at the
address position was not an accurate measure at the top of the backswing or at
impact.
In relation to swing planes, Coleman and Rankin (2005) utilised 3-D
kinematics to demonstrate, contrary to many previous models and coaching theories,
that the left arm and shoulder girdle do not move in a consistent plane throughout the
downswing, thereby calling for more complex and realistic models for future
simulations. In a subsequent study, Coleman and Anderson (2007) concluded that it
was mathematically possible to fit a single plane to the 3-D downswing motion of the
golf club for experienced golfers, but the fit varied between golfers and also between
clubs (driver, 5-iron and pitching wedge).
The means by which high club head speed is generated has remained topical.
The kinematic chain involving hip and thoracic rotations followed by sequential
actions of the arms, forearms and wrists has been studied. In an experimental study,
Teu et al. (2006) provide a novel method of velocity analysis using dual Euler
angles, which they showed provides an option in assessing the contributions of
individual segment rotations in the production of the relevant velocity of the end-
effector. Sprigings and Mackenzie (2002) carried out a simulation study to examine
the effects of a delayed wrist release technique (uncocking) and to identify the
sources of power that account for increasing club head speed. These authors showed
a small advantage in employing this delayed release at the wrist, but the magnitude
of the gains were significantly less than previously reported. Their simulations also
provided muscle power magnitude values for the shoulders, wrist and torso that
contributed to the swing.
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Combined with biomechanical analysis, research using launch monitors has
permitted investigations into the mechanisms by which club head velocity is
generated, and the subsequent ball launch characteristics. Fradkin et al. (2004) found
a strong linear relationship between golfers’ mean club head velocity at impact and
handicap. As handicap increased, club head velocity at impact decreased. An
equation was derived (Equation 1.1) whereby, using the 45 golfers studied, club head
velocity could be derived from handicap, thus:
Mean club head velocity = e 4.065 – 0.0214 x handicap (1.1)
Previously, Wallace and Hubbell (2001) studied 84 golfers with a wide range of
handicaps to determine relationships between club head speed for 5-irons and
various anthropometric measures, physical fitness factors and handicap. The
regression equation for statistically significant partial correlations with club head
speed is given in (Equation 1.2).
CLUBHEAD SPEED = [90.05 (+/- 16.06)] – [0.898 (+/-0 .29) HANDICAP] +
[0.109 (+/- 0.07) BACK STRENGTH] + [11.82 (+/- 7.75) LEG POWER]. (1.2)
Wallace et al. (2007) described the ball launch characteristics of ball velocity,
spin and launch angle for skilled golfers using long drivers using a stereoscopic high
speed launch monitor. They concluded that all drivers demonstrated similar ball
launch characteristics, but the longest driver of 52" yielded small, but significant,
gains in ball velocity compared to the other drivers studied. Similarly, Kenny (2006)
reported increased club head velocity when elite golfers used a driver of 50", some
2" longer than the current length limits. Recently, the role of the upper torso and
pelvis rotation in producing high ball velocity has been re-visited with 3-D
kinematics combined with launch monitor data (Myers et al., 2008). These authors
refer to the ‘X-factor’ term commonly used by teaching professionals and reported in
many scientific studies, or ‘segment separation’ as the difference in axial rotation
between the upper torso and the pelvis at the top of the backswing. However, while
using the global x-axis, as opposed to employing Cardan angles as outlined by
Wheat et al. (2007), Myers et al. (2008) showed torso-pelvis separation during the
swing contributes to greater upper torso rotation velocity and torso-pelvis separation
velocities during the downswing, thereby resulting in greater ball velocity. McCloy
et al. (2006) also characterised ball launch conditions and club head velocity for a
range of irons and elite level golfers. They found that as loft increased, club head
velocity decreased, as would be expected, but also that club head angle of attack, or
dynamic loft, increased. These findings contribute towards a baseline reference for
future studies that may seek to determine specific iron club features, such as shaft
dynamic stiffness effects. Research relating to driver shot performance appears to
have concentrated on club head velocity and ball velocities as they relate to distance.
Few studies have investigated accuracy, except for example those by Werner and
Greig (2000) and Kenny (2006). Another issue relates to ecological validity (Wheat
et al., 2007) due to the bulk of biomechanical analyses being conducted in the
laboratory.
Ball and Best (2006) in their examination of weight transfer patterns using
cluster analysis identified two major centre of pressure (COP) patterns during the
downswing that were evident in both professional, highly skilled golfers as well as
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high handicap players, thus indicating neither style was a technical error. Later, Ball
and Best (2007) demonstrated specific and unique positioning and range of COP for
each style, leading them to the conclusion of the importance of identifying different
movement strategies before evaluating performance measures. Biomechanics
researchers such as Hatze (2005), and noted by Farrally et al. (2003) have indeed
discussed the need for subject-specific investigation into human motion by means of
computer models and movement simulation. Development of models that are
anthropometrically tailored for individual subjects are called for, thereby providing a
better correlation between experimental and theoretical results. Kenny et al. (2006)
developed a large-scale full-body musculoskeletal model to investigate the
kinematics and kinetics of the golf swing for an elite golfer. The model was driven
using three dimensional movement data from one subject (a plus-1 handicap golfer).
Computer simulations replicated the swing of the golfer with a correlation of 0.999
between experimental kinematic data and simulated kinematics. Figure 1.2.1 shows
an image of a simulated swing using a driving club. Such a model could be used to
further investigate the hip and shoulder kinematics, characterisation of swing planes
and timing, as well as club-hand kinetics and muscle forces generated.
Figure 1.2.1 Musculoskeletal golfer model
Similar models have been developed using biomechanical modelling software by
Nesbit (2005) and Nesbit & Ribadeneira (2003) investigating the work and power
outputs by the golfer during a golf swing. They found that joint torque was markedly
different between subjects, but concluded that factoring in different swing speeds,
the energy losses at impact, and club aerodynamic drag resulted in a reliable
simulation of the kinetics of the golf swing.
1.3 GOLF PSYCHOLOGY
Since Farrally et al.’s (2003) review of golf science at the start of the 20th Century,
research into the psychology of golf has continued to flourish. In the context of this
chapter, golf psychology research encompasses studies that use golfers as the
participant population, as well those explicitly utilising golf tasks to examine a
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specific psychological aspect of sport. This is not to say that there are not numerous
studies across the gamut of theoretical areas comprising sport psychology, the
findings of which would readily transfer to golfers and golf type sports. The research
has taken (and appeared in) a number of forms, however, for the purpose of this
overview, we are only going to describe research findings communicated through
peer-reviewed academic research journals. Broadly speaking, the three areas of sport
psychology that have received concerted attention with respect to golf are: stress and
coping; the use of imagery; and focus of attention. We are not in any way suggesting
that there has not been other golf related research in sport psychology since 2003;
indeed, within conference presentations and on-line sport science resources, work
has been presented in the areas of motivation, the yips and choking, and the
caddie/golfer relationship, for example.
Players and coaches continue to recognise the importance of psychological
skills in golf, particularly at the highest level (Thomas, 2001). Indeed, it is a
relatively recent phenomenon to observe at least four or five practising sport
psychologists supporting clients at a typical European Tour golf event. This ‘coming
out’ of the discipline at an applied level makes it incumbent upon the academic
community to ensure that applied sport psychology is supported by good science
practised within meaningful, well conceived, ecologically valid research studies.
Farrally et al. (2003) in their review acknowledged that there had been significant
research in the areas of: stress and anxiety; performance routines; process goals;
mood state; personality; attention; and imagery. It would be reasonable to suggest
that in a few areas this work has moved forward, however, in others the status quo
has remained. As mentioned previously, our search of the peer-reviewed journal
literature illustrates significant developments in the areas of: imagery; stress
(specifically sources and coping strategies); and focus of attention it is this work,
we will now briefly review.
Imagery, as well as being identified as a pivotal psychological skill for
golfers, has in recent years become very popular amongst sport psychology
researchers. The efficacy of a structured imagery training programme has been
consistently supported (Munroe et al. 2000). Building upon this momentum, Smith
and Holmes (2004) sought to identify the most effective imagery modality for
enhancing putting performance using a sample of 40 male golfers (mean handicap =
3.54). Their results indicated that in comparison to self teaching (through reading)
and following a script, video (self-modelling) and audio modes were more effective
in improving performance. They concluded that imagery training should allow the
participant to experience the motor representation of the skill as fully as possible.
This supports the proposal that imagery of movement exercises and encodes the
relevant brain areas which in turn facilitates performance (cf. Smith and Holmes,
2004). Gregg and Hall (2006) examined the magnitude of, and the influence of age
and skill level on imagery use. Supporting the contentions of Cumming and Hall
(2002), with regards to the relationship between imagery use and deliberate practice,
Gregg and Hall found that as handicap level increased (i.e. players were less skilled),
imagery use decreased. They also reported that imagery use decreased with
advancing years, suggesting that imagery training should be an integral part of
physical skill development in golf. Finally, they noted that, factors such as setting
(i.e. practice versus competition), time of season, and confidence levels also impact
on imagery use.
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Previous research has illustrated the potentially debilitating effects of
psychological stress on golf performance (e.g. Hardy and Mullen, 2001; Masters,
1992). Clarifying this relationship, Hassmen et al. (2004) suggested that variability
in athlete perceptions of their physiological arousal (somatic anxiety) was
significantly related to variability in actual performance, suggesting that self-
regulation and coping strategies are critical for effective performance. Associated
with this proposal, there is an increasing body of research literature concerned with
sources of such stress, and more specifically the strategies for coping with stressors
in golf. Nicholls et al. (2005), examined the coping strategies of eighteen
international age-group golfers, and found that effective cognitive coping strategies
were employed. These included, for example; rationalising mistakes, thought
blocking, reappraising, positive self-talk, and adhering to their routine. These
paralleled many of the findings of Giacobbi et al. (2004) who, in examining the
coping responses of skilled and moderately skilled golfers, found that golfers used
more than one coping strategy; further, their strategies included such things as
maintaining a positive perspective in the face of adversity, interpreting information
positively, and/or retaining a positive focus. Again, in terms of frequency, Nicholls
et al. (2005) found that, although a wide range of specific stressors have been
identified in the literature, for any given athlete, there were actually a relatively small
number of acknowledged stressors, but these were experienced repeatedly.
Furthermore, as the season progressed, golfers reported that mental errors occurred
more frequently than physical errors, illustrating the value of ongoing sport
psychology support for athletes throughout the season.
In the past ten years there has been a thrust in attempts to identify and
clarify the most appropriate focus for a performer’s attention while executing skills.
Based on the work of Wulf and associates (e.g. Wulf et al. 1999; Wulf and Prinz,
2001), it has been argued that a focus on bodily movements (an internal focus of
attention) is less effective than paying attention to the anticipated environmental
effects of one’s movements (an external focus of attention), for example, the
proposed target. More specifically, Perkins-Ceccatto et al. (2003) using a golf
pitching task, found that highly-skilled golfers performed better with an external
focus of attention, yet low-skilled golfers performed better when focusing on the
form of their swing and the force required to hit the ball a set distance. They
concluded that, once the fundamentals of the skill have been learned, performers will
benefit most from concentrating on the effects of their movement, rather than by
attending to the action of the golf stroke. Conversely, before the fundamentals are
grasped, it is better to concentrate on the movements required to achieve this
objective. Clearly this has important implications for coaching golf.
In addition to carrying out research using refined and more ecologically
valid methodologies to build on previous work, preliminary theory-building work in
other areas of sport psychology has opened the door for future research in golf. This
research has the potential to prove fruitful in further informing applied practitioners.
The efficacy of pre-performance routines is not in any doubt (see, Jackson, 2001)
however, understanding the mechanisms behind their positive effects may enable
them to be taught more efficiently. Further, there have been a number of major
theoretical developments in areas such as: sources of confidence, motivational
profiling, and mental toughness. These advances will enable those with a specific
interest in golf science to engage in research that is both well-grounded conceptually,
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and also has the potential to inform teaching, coaching, and skill development within
the sport.
1.4 GOLF TECHNOLOGY
The development of golf equipment has been a feature of the history of golf and
continues apace. Whilst much historical development has been empirical, recently
there has been much more systematic study into equipment and its operation aided
by increased development of high-speed imaging and measurement equipment.
These techniques have allowed a more quantitative determination of the dynamic
performance of equipment and of materials properties. Knowledge of more
appropriate properties means that models, such as finite element, are more accurate
and can be used in a more predictive capacity in optimising equipment design and
tailoring it to specific golfers.
Throughout most of the 1990s, one of the major issues in equipment
technology was that of high coefficient of restitution (CoR) drivers, which, coupled
with the introduction of Titleist ProV1 and ProV1x solid golf balls, resulted in a
steady increase in drive distances. As Fig. 1.3.1 shows the major increases in drive
distances occurred between 1993 and 2000 as titanium-based alloys were used in
hollow, oversized drivers. During this period the use of forged metastable β-Ti
alloys with higher strength / modulus ratios than the cast α + β titanium-based alloys
originally used, coupled with control of the size and position of joints between face,
crown and sole resulted in drivers approaching the USGA / R&A CoR limit. Thus,
the rate of drive distance increase has slowed considerably over the period 2003 –
2007, Fig. 1.4.1.
Average US PGA Tour Drive Distances
Year
1980 1985 1990 1995 2000 2005
Drive distance (yards)
255
260
265
270
275
280
285
290
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Figure 1.4.1. Variation in average US PGA drive distances with year (each point
represents around 32,000 measurements). The increases prior to 1993 are largely
associated with golfer conditioning and training, whilst the sudden increases in 2001
and 2003 are associated with ball variations. [Graph constructed from data on US
PGA website - accessed 5/06/07]
Drive distances are largely associated with ball speed off the driver face,
which is achieved by reducing head stiffness so that viscoelastic ball deformation,
which loses energy during impact, is replaced by linear elastic head deformation
(with negligible energy loss). As fully metallic alloy heads are reaching the
conformance limit, then the focus of research has moved away from outright distance
to increased control and modified launch conditions. This increased ‘forgiveness’ of
drivers is achieved through both mechanical design and material usage. The change
in materials is often achieved through combination of a titanium-based alloy face and
sole with a carbon fibre composite crown. The introduction of a polymer matrix
composite increases the viscoelastic nature of deformation during impact of the head
which will increase the energy loss during impact and so will compromise absolute
CoR. However, the substitution of lower density composite material (1.7 g cm-3) for
β-Ti (4.7 g cm-3) results in the ability to re-distribute mass lower in the head to
modify launch conditions, particularly increasing launch angle. In mixed material
heads the face and sole are constructed from Ti-based alloys due to the poor wear
resistance of epoxy resin matrix systems. Whilst allowing mass redistribution the
incorporation of polymer matrix composites introduces potentially greater material
variability, as has been noted in carbon fibre composite shafts (Huntley et al., 2006),
Fig. 1.4.2, as well as a greater rate-dependence to the head properties.
(a)
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(b)
Figure 1.4.2. (a) Variation in fundamental bending frequency around the
circumference of a carbon fibre composite shaft associated with variations in fibre
volume fractions through the cross-section of the shaft (b); the fibres appear as light
dots.
The strain rate-dependence of composite material properties has
traditionally been limited to static and crash situations, i.e. mainly at very low and
very high speeds, which are not appropriate to sporting situations such as golf, tennis
and skiing. Investigations into dynamic properties over more representative
deformation rates have identified relationships between material properties and
performance for shafts and balls (Strangwood et al., 2006) leading to more accurate
and predictive models (Rowe, 2007). Extension of these studies to composites in
drivers along with improved homogeneity in properties may lead to incremental
improvements in the performance of drivers, but are unlikely to give effects as large
as those seen in the 1990s. The majority of work in this area has been carried out by
major manufacturers, leading to clubs such as the Mizuno MX-500 (Mizunousa,
2007), but with few open reports apart from patents.
The use of lower density materials with higher strength allows downgauging
of sections increasing the amount of mass available for redistribution as well as
facilitating less traditional head shapes. This has allowed ‘squarer’ heads, such as the
FT-i (Callaway, 2007) and Sasquatch (Nike, 2007) with larger moment of inertia
(MoI) values to be developed. Higher MoI values reduce the rotation of the head
during the downswing and impact and so reduce the variability in impact conditions
for a range of swings. As such, they offer little in terms of performance increase for
golfers with consistent swings, but are more forgiving of golfers with less consistent
swings. This effect will also have its limit (USGA and R&A conformance limits), but
there will be incremental improvements as the materials (e.g. higher strength
nanocomposites), their homogeneity and their dynamic properties are optimised to
high MoI designs.
Whilst the head is important, much work is continuing into increased
understanding of the behaviour of golf shafts during the golf swing, particularly with
a view to optimising shaft performance to individual golfer’s swings. This is
concentrating on carbon fibre composite shafts due to the design flexibility provided
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by sheet laminate lay-up (Lee and Kim, 2006; Kim et al., 2006). These studies will
need to address the inhomogeneity and dynamic issues mentioned above, but
indicate greater interest in the dynamic interaction of the golfer and their equipment.
This will assume more importance in future research with enhanced
interdisciplinarity between materials, mechanical engineering, biomechanics and
psychology.
Finally, the use of high-speed imaging has allowed the interaction of golf
balls with normal and inclined plates (grooved and un-grooved) to be quantified and
related to material properties and ball construction. This has been accomplished for
both normal impact, i.e. distance (Johnson, 2005; Strangwood et al., 2006), and
oblique impact, i.e. spin generation (Monk et al., 2005; Cornish et al., 2006). These
studies have identified material property ranges necessary for spin generation –
interaction of a soft cover with grooves on the face, with a soft core to give a large
contact area on impact, but separated by a hard mantle to reduce viscoelastic losses
and maintain speed off the face. These trends and the greater understanding of the
effects of graded material properties are borne out by the performance of recent
three- and four-piece balls. Coupled with better models of ball behaviour (Rowe,
2007; Tanaka et al., 2006) and more appropriate data (Mase and Kersten, 2004) the
design of balls appropriate to particular swing speeds is possible.
1.5 CONCLUSION
Golf remains a popular and topical sport for research. Since 2003, biomechanical
studies have continued to examine the kinematics of the swing with some additional
knowledge gained in terms of kinematic chain motion. A rationalised coordinate
system for studying hip and torso rotations during the swing has been suggested, that
may provide a further understanding in the future of the generation of end-effector
velocity. The need for consideration of human variability in the golf swing has been
reinforced, with some advancement made in terms of representative simulation
models. Future work should aim to validate laboratory-based tests so that further
‘ecologically’ sound experimental investigations can be conducted, which in turn
could be used with simulation models that have the sophistication to produce
realistic results, yet without unnecessary compromising complexities. In psychology,
post Farrally et al.’s (2003) review, a number of significant developments have been
identified in, for example, the fields of: imagery, sources of stress and coping, and
identifying an optimal focus of attention. The major implications of this work
suggest that: a) imagery training should be an integral part of golf skill development,
and the nature of this training should be tailored according to the context, and the
confidence and the skill level of the performer; b) in absolute terms, individual
golfers experience a small number of stressors, but these stressors often reoccur
throughout their round they also use a variety of strategies even to cope with the
same stressor; c) once the fundamentals of the golf swing are mastered, learners will
benefit most from focusing their attention on the effects of their swing, rather than
attending to the action itself. Future work, as well as building on current knowledge
bases, should consider theoretical developments in, for example areas of confidence,
motivation and mental toughness. The large market for golf equipment and for
technology to aid golfers means that this will continue to be a fertile ground for
innovation. Recent studies have shown a more systematic approach to enhance
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understanding of the dynamic phenomena involved. This has allowed real effects to
be determined and optimised through materials, design and construction. Future
trends appear to be towards greater understanding of the interaction of the golfer
with their equipment so that tailoring of equipment for a wider range of abilities
rather than just the elite will become possible.
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