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In recent years, golf has experienced a considerable increase
in popularity (Farrally et al., 2003;
Theriault and Lachance, 1998).
Interest in this sport has reached the scientific community and a growing
body of research analyzing the requirements of competitive golf performance
is being published. In a relatively recent review, Farrally et al., 2003
summarized the results of golf-related investigations published by the
World Scientific Congress of Golf (WSCG), and identified the main areas
of interest. One of these areas comprises issues related to physical conditioning,
exercise and nutrition (Carlson et al., 2001;
Crews and Landers, 1987;
Crews et al., 1986;
Cheetham et al., 2001;
Chettle and Neal, 2001;
Etnier et al., 1997).
According to the aforementioned authors, physical demands in golf are
yet not well understood, even though growing attention is being paid to
increasing muscle strength and flexibility to optimize driving distance.
Scientific research about physical conditioning to improve golf performance
is scarce, and most investigations regarding the mechanics of the golf
swing and innovation in golf equipment and materials have been carried
out by golf manufacturing companies (Farrally et al., 2003).
It is generally accepted that one of the most important determinants of
golf performance is the resulting combination of accuracy and driving
distance (Hetu et al., 1998;
Hume et al., 2005;
Sthromeyer, 1973;
Yoon, 1998).
The drive shot is especially relevant given that it usually has to cover
the longest possible distance. The strategy to play the hole must be adjusted
depending on drive shot success (Thompson et al., 2007).
Driving distance correlates with average score in elite golfers, (r =
-0.24 to -0.50) which may determine the difference in total score (Hale
and Hale, 1990;
Riccio, 1990;
Wells et al., 2009;
Wiseman and Chatterjee, 2006).
This finding is in agreement with those obtained by Cochran and Stobbs,
1968,
who concluded that a 17 m increase in drive distance alone (no change
in accuracy) would result in an improvement in golf score of 2.2 strokes
per 18 hole round.
Driving distance is influenced by many factors, the most important being:
skill, kinematics, shaft and club head characteristics, segmental sequence
of action and power output reached (Fletcher and Hartwell, 2004;
Milburn, 1982;
Wiren, 1968;
Yoon, 1998).
Thus, it seems clear from these factors that a better understanding of
the muscular implications and strength requirements of the swing would
contribute to optimize physical conditioning for improving golf performance.
Several studies have analyzed the effect of different resistance-only
training programs or combined routines (also including endurance, flexibility
and balance training) on swing performance variables (Doan et al., 2006;
Fletcher and Hartwell, 2004;
Hetu et al., 1998;
Landford, 1976;
Lennon, 1999;
Lephart et al., 2007;
Seiler et al., 2006;
Thompson et al., 2007;
Thompson and Osness, 2004;
Westcott et al., 1996).
Despite quite different methodological designs, these studies seem to
indicate a positive influence of strength and power development on golf
performance.
The aim of this review is to examine the existing scientific literature
regarding strength training and golf in healthy, non-injured, subjects.
The strength assessment and training methods commonly used will be discussed
and new lines of investigation suggested. It is expected that some conclusions
can be reached that provide valuable guidance to coaches and fitness trainers
on how to train muscle strength for improving golf performance.
Literature
search
A literature search was conducted in the following databases: PubMed (National
Library of Medicine, USA), SPORTDiscus (Sport Information Resource Centre,
Ontario, Canada) and UMI Dissertation Service (ProQuest, Canada) using
the keywords 'golf', 'swing performance', 'driving distance', 'ball speed',
'club head speed', 'strength', 'resistance training' and 'power'. The
'Science and golf' peer-reviewed proceedings of the WSCG book series between
1990 and present was reviewed. Manual searches in reference lists of selected
published papers were also performed. The search yielded a total of 45
relevant documents which were carefully examined.
Relationship
between skill level, swing performance and muscle strength
Relationship
between swing performance and skill (handicap and score)
Several variables commonly used as outcome measures in golf research are
closely related to one another and may be considered equivalent in terms
of golf performance: club head speed (CHS), driving distance and ball
speed. A relationship between these swing performance variables and handicap
(HCP) has already been established. Fradkin et al., 2004
found a negative relationship between 5-iron CHS and handicap (r = -0.95;
p < 0.001). Age and frequency of play, on the other hand, were found
to have no significant impact on handicap variance. These results indicate
that golfers with lower handicap (better skill level) have a faster CHS,
regardless of age and training frequency. Even though this study did not
test golfers' accuracy, the authors acknowledged its great importance
in the game since players not only need to hit the ball a long distance
but they also require their shots to be accurate. Smoliga et al., 2006
analyzed swing performance indicators for three groups of golfers differing
in skill level: low (n = 56, HCP < 8), middle (n = 25, HCP: 8-14.9)
and high handicap (n = 9, HCP = 15). Significant differences were observed
in ball speed, carry distance and total driving distance between high
handicap golfers and the most skilled group. No significant differences
were found between groups for backspin or club speed. The authors suggested
that consistent ball flight characteristics are a key contributor to golf
proficiency. In a similar study, Keogh et al., 2009
found that a low-handicap group (LHG) (n = 10; HCP 0.3 ± 0.5) had faster
(+12%; p < 0.001) CHS than a high-handicap group (HHG) of golfers (n
= 10; HCP 20.3 ± 2.4), which coincides with the results obtained by Fradkin
et al., 2004.
Wiren, 1968
found that handicap was the best single predictor of driving distance
(r = -0.61) while Sell et al., 2007
reported a significant correlation between CHS and driving distance (r
= -0.48; p < 0.001). Therefore, a positive relationship seems to exist
between handicap and swing performance variables, although there are still
relatively few studies that have examined this issue.
Relationship
between muscle strength and skill (handicap and/or golf score)
Studies that relate skill (handicap or score) to muscle strength are scarce.
Kras and Abendroth-Smith, 2001
studied the relationship between some fitness variables (body composition,
flexibility, balance, cardiovascular endurance, grip endurance, grip strength
and leg power) and an average score based on the last six reported golf
scores during league completion in a group of 56 junior high-school golfers.
Handicap was not considered. With regard to muscle strength, significant
relationships were found between average golf score and leg power (standing
long jump test) (r = -0.36; p < 0.05). Similarly, Wells et al., 2009
observed a significant correlation between total score and muscle performance
(vertical jump, push-ups/pull-ups in 60 s and grip strength). Grip strength
showed the highest correlation to score, both in the dominant (r = 0.68;
p < 0.001) and non-dominant arm (r = 0.71; p < 0.001). Tsai et al.,
2004
measured isometric hip abduction and adduction strength in side-lying
with the hip joint in neutral position and normalized to body weight for
both legs using a dynamometer. They found a negative correlation between
left hip abduction and handicap (r = -0.33; p < 0.05). Sell et al.,
2007
analyzed a sample of 257 male golfers and found that players with scratch
(zero handicap) or better handicap obtained significantly better results
in hip muscle, trunk and shoulder strength (isokinetic strength at 60º·s-1)
than less proficient golfers. Taken together, and despite that the strength
assessment procedures greatly differed between studies, these results
suggest that there is a positive correlation between skill (handicap or
golf score) and muscle strength, especially grip strength. This relationship
seems to be observed in adult golfers as well as in junior players. Further
investigations should be carried out to confirm these findings.
Relationship
between muscle strength and swing performance
Studies investigating the relationships between physical fitness variables,
ball speed and performance (Bayios et al., 2001;
Carlson et al., 2001;
Ferris et al., 1995;
Forthomme et al., 2005;
Heitman et al., 2000;
Pugh et al., 2003;
Pyne et al., 2006;
Signorile et al., 2005)
are common for sports such as baseball, tennis, volleyball and handball.
Table 1 summarizes the results of
a limited number of studies which analyzed the relationship between muscle
strength and golf swing performance variables.
Yoon, 1998
measured muscle strength and its relation to swing speed. He observed
a significant correlation between swing speed and combined leg and hip
muscle power (r = 0.37), grip strength (r = 0.29), trunk power (r = 0.63)
and combined trunk and arm strength (r = 0.33). In a stepwise multiple
regression analysis, power factors (trunk power, hand grip strength and
normalized leg and hip power) were meaningful in predicting swing speed,
with trunk rotation strength as the most significant predictor. Thus,
a significant relationship was observed between muscle trunk power and
swing speed in elite golfers (HCP < 3). However, one possible drawback
of this study would be the small sample size (n = 14) and the wide age
range (18-38 yr) of participants. Wu et al., 2007
observed a significant correlation between ball speed and left hip (abduction
r = 0.56; flexion r = 0.60), trunk (flexion r = 0.52; extension r = 0.56)
and right shoulder (internal rotation r = 0.63; external rotation r =
0.60) muscle strength. These findings agree with those of Tsai et al.,
2004
who found that left hip abduction strength correlated to driving distance
(r = 0.32; p < 0.01). Even though the number of participants (n = 82)
was high, some important limitations were observed: the authors did not
report the players' age and driving distance was not evaluated but self-reported.
Other recent studies have correlated swing performance indicators to muscle
strength and power, in addition to other physical fitness variables such
as flexibility, endurance, balance and anthropometric measurements. Wiren,
1968
examined factors that could influence driving distance and categorized
them under four different headings: strength, anthropometry, flexibility
and timing. As a result, 13 strength-related items showed correlation
with driving distance, the most significant ones being: right wrist palmar
flexion strength (r = 0.59), right ankle plantar flexion strength (r =
0.49) and left shoulder horizontal extension strength (r = 0.48). Age
showed a correlation of r = 0.55. Wiren, 1968
suggested that strength and timing seem to be the factors most related
to driving distance. Wells et al., 2009
linked several physiological measures to golf performance. The authors
established the following categories of analysis: balance, flexibility,
abdominal muscle performance, peripheral muscle performance (upper- and
lower-body) and golf performance. When analyzed by gender, female results
revealed trends and significant correlations between dominant leg vertical
jump and drive ball speed (r = 0.57; p < 0.05) and driving distance
(r = 0.61; p < 0.01). Results from male participants indicated significant
correlations between vertical jump and drive ball speed (r = 0. 50; p
< 0.05) and driving distance (r = 0.62; p < 0.01); between pull-ups
and drive ball speed (r = 0.55; p < 0.05) and distance (r = 0.53; p
< 0.05); between push-ups and drive ball speed (r = 0.48; p < 0.05);
and between grip strength and drive ball speed (r = 0.65; p < 0. 01).
Gordon et al., 2009
investigated the relationship of strength, power and flexibility to CHS.
The results showed a significant correlation between chest strength and
CHS (r = 0.69; p < 0.05), and between total body rotation power (distance
reached with a 3 kg medicine ball with a hip toss movement) and CHS (r
= 0.54; p < 0.05), in a group of 15 male golfers (HCP 4.9 ± 2.9). Keogh
et al., 2009
compared a group of 10 LHG (HCP 0.3 ± 0.5) with a group of HHG male golfers
(HCP 20.3 ± 2.4). Results showed that strength in golf-specific cable
woodchop exercise was significantly greater in LHG than HHG, and significantly
correlated to CHS. Trends were also evident for bench press strength,
greater in LHG than in HHG and significantly correlated to CHS. Thompsom
(2002)
observed that strength variables (10RM in chest press, leg press, lat
pulldown, shoulder press, biceps curl, and seated row exercises) in recreational
older golfers (n = 31) showed a significant relationship with CHS. In
this case, it would have been adequate to consider the addition of skill
level (handicap or score) to the list of dependent variables in order
to analyze strength in differently skilled subjects.
After reviewing all these studies, a relationship seems to exist between
muscle strength and golf performance variables (i.e. driving distance,
CHS, ball speed). However, it must be taken into consideration that the
methodological approach of the examined studies was very different. While
Gordon et al., 2009,
Keogh et al., 2009,
Wells et al., 2009
and Yoon, 1998
measured muscle power at least in one golf-specific exercise, other investigations
(Tsai et al., 2004;
Wiren, 1968;
Wu et al., 2007)
determined muscle performance from strength values obtained from various
types of isometric or isoinertial tests which bear little resemblance
to golf actions. After reviewing the results, and due to the differences
in assessment methodology (different muscle groups and type of muscle
groups and actions evaluated), it is not possible to determine whether
driving distance or swing/ball speed are more related to trunk and upper-body
or to lower-body strength. Nevertheless, the results suggest that leg,
hip and trunk power, as well as grip strength are especially relevant
to golf performance. It is also worth noting that the profile of the participants
in these studies is quite heterogeneous in relation to handicap (skill
level) and age, which makes it difficult to generalize the obtained conclusions
to other populations. Most of the reviewed papers analyzed the relationship
between some physical fitness variables and swing performance, which is
critical to establish the physical conditioning requirements of golf.
However, only three of the aforementioned studies (Tsai et al., 2004;
Wu et al., 2007;
Yoon, 1998)
have delved into the relationship between muscle strength and swing performance,
which proves insufficient to establish causality. Further research should
address the relationship between muscle strength and power in trunk, upper-
and lower-extremities and swing performance in order to understand how
these variables affect the kinematic sequence of the golf swing, especially
in elite golf players.
Changes
in swing performance as a consequence of strength training
Most
of the studies that have analyzed changes experienced in golf swing following
a training program emphasizing muscle strength, power, flexibility, plyometrics,
balance, or a combination of any of these physical fitness components,
have showed statistically significant improvements in some or all of the
variables related to swing performance. Although some exceptions do exist
(Pinter, 1992;
Reyes, 2002),
when an improvement in strength has occurred, a subsequent increase in
ball speed has always been observed regardless of the type of strength
training program undertaken.
Following training, increases in club head speed (1.6-6.3%) have been
observed (Doan et al., 2006;
Fletcher and Hartwell, 2004;
Hetu et al., 1998;
Lennon, 1999;
Lephart et al., 2007;
Seiler et al., 2006;
Thompson, 2002;
Thompson et al., 2007;
Thompson and Osness, 2004;
Westcott et al., 1996).
Lephart et al., 2007,
Thompsom et al. (2007),
Seiler et al., 2006,
Hetu et al., 1998
and Westcott et al., 1996
obtained the most noticeable improvements. It is worth mentioning the
results obtained with regards to driving distance, where increases of
4-5% have been reported (Fletcher and Hartwell, 2004;
Landford, 1976;
Lephart et al., 2007;
Wenzel, 1968).
Results
obtained following a strength training program
Landford, 1976
studied the effects of a 10-wk strength training program (Table
2) on driving distance and accuracy (approach test), in a sample of
42 subjects (32 males and 10 females) who were divided into two groups:
experimental and control (HCP < 10). Significant improvements (p <
0.01) were observed in all analyzed variables except the approach test.
According to the author, strength training had a positive influence in
driving distance, without having negative effects on accuracy. In contrast,
Reyes, 2002
did not find any significant increase in driving distance in low- and
high-handicap golfers (HCP 19 ± 9 vs. 21 ± 8 for the experimental and
control groups, respectively) following a training-induced increase in
maximal isometric strength. However, since the swing implies a complex
kinetic chain of muscle actions, using maximum isometric force measurements
to assess muscle strength for golf is somewhat questionable.
Due to the very few existing studies that have analyzed changes in golf
swing performance following a resistance-only training program, it is
not possible to discern whether the observed improvements are related
to strength gains or other factors. Thus, the results obtained so far
are inconclusive and additional research is warranted.
Results
obtained following a combined training program
Several studies have analyzed changes in swing performance indicators
following a conditioning program in which strength training was combined
with other physical fitness components (flexibility, balance, cardiovascular
endurance, etc.). In the study of Fletcher and Hartwell, 2004,
11 golfers (29 ± 7.4 yr; HCP 5.5 ± 3.7) took part in an 8-wk combined
training program of general strength and plyometrics (Table
2). Following training, an improvement in golf performance (+1.5%
in CHS and +4.3% in drive distance) was observed in the experimental group
(n = 6) whereas no significant changes were found in the control group
(+0.5% in CHS and -0.7% in drive distance; n = 5). Authors assumed that
changes in drive performance were due to an increase in muscle strength.
In the investigation of Seiler et al., 2006,
the experimental group followed a 9-wk core and rotational stability training
program while the control group performed a standard strength training
program for the same time period. The experimental group obtained better
results with an increase of 3.8% in CHS (95% CI: 2.6-4.8%; p < 0.001)
compared to 1.2% for the control group (95% CI: 0.0-1.0%; p < 0.05).
Nevertheless, in these two studies no physical conditioning assessments
were conducted, thus it is impossible to determine if the observed changes
in driving performance and club head speed are a consequence of strength
or balance training. Doan et al., 2006,
observed significant (p < 0.05) pre- to post-training improvements
in all measures, after an 11- wk strength (Table
2), power and flexibility program (+7-24% in strength, and +7-16%
in flexibility). In this study, qualitative video analysis and putting
distance control tests were used. Contrary to their hypothesis, there
were no differences between pre- and post-training putting test values.
The results showed an increase in CHS (+1.6%) without a negative impact
on putting consistency in elite golfers, even though relationships between
strength changes and CHS were not indicated. Lephart et al., 2007
examined the effects of strength (Table
2), balance and flexibility following an 8-wk golf-specific exercise
program. A biomechanical analysis of swing mechanics was included. Results
showed significant improvements (p < 0.05) for right torso rotation
strength at speeds of 60º·s-1 (+7.5%) and 120º·s-1
(+13.3%), and left torso rotation at 60º·s-1 (+8.9%), isometric
hip strength (left hip abduction: 8.6%; right hip abduction: 9.9%; left
hip adduction: 8%), range of motion, and left-leg balance between pre-
and post-training. These changes led to an improvement of the effectiveness
indicators of the swing (+7.7% carry distance; +6.8% total distance; +5.0%
ball velocity; +5.2% club speed). Thompson and Osness, 2004
examined senior golfers involved in an 8-wk strength and flexibility program.
Following training, significant improvements were observed in club head
speed (+2.7%). Strength measurements improved significantly (+60.4% biceps
curl, +35.6% chest press, +38.3% shoulder press, +36.9% seated row, +41.1%
leg press and +38.5% leg extension; p < 0.05). In a second study (Thompson
et al., 2007),
improvements in club head speed were observed (+4.9%) following strength,
cardiovascular endurance, flexibility and dynamic balance training. Improvements
in 30-s chair stand test and 2-min step test were also significant (p
< 0.05). These results are similar to those reported by Hetu et al.,
1998
and Westcott et al., 1996
who studied changes in golf performance following a strength (Table 2) and flexibility training program. Significant increases
in several physical fitness measurements (+6.2% grip, +14.2% chest press,
+18.1% leg extension and +47.3% trunk rotation) were related to an improved
drive performance (+6% in CHS). Research carried out by Lennon, 1999
included two studies: in the first one, subjects participated in an 8-wk
strength and flexibility training program; while the second one showed
the effects of a 1-yr strength, flexibility, endurance and balance training
program (details of the programs were not disclosed). The author suggested
that an improvement in physical condition and golf performance was observed
in both cases, but he did not report a detailed description of the extent
of the improvements (Table 2). Pinter, 1992
examined the effects of strength (n = 6), flexibility (n = 6) and a combination
of both types of training (n = 7) on drive CHS. Following 8-wk training
(Table 2), the author did not find
any significant differences between pre- and post-tests in ball speed.
This lack of statistical significance could be explained by the low number
of subjects included in each group as well as the instructions to 'swing
as in competition' as opposed to 'swing for maximum distance' when the
drive test was performed. Moreover, since in this study there were no
pre-post strength assessments, it is not possible to determine whether
the results were a consequence of changes in muscle strength levels.
From the above data, it would seem that improvements in strength, combined
with flexibility and balance training can lead to an increase in CHS,
ball speed, carry distance and total distance. However, these investigations
present several methodological limitations worth noting. In some studies
no strength assessments were conducted. In addition, there is a lack of
analysis of changes in muscle strength levels following training and its
results on swing performance. Indeed, this may be the reason why it is
not possible to reach significant conclusions about the relationship between
both variables. Carefully controlled studies with better experimental
designs should be carried out in order to assess the influence of different
types of strength training on golf swing performance.
Methodological
issues
Strength
assessment in golf
Investigations examining strength and its relationship to golf performance
have been characterized by the use of different methodologies to assess
muscle strength and/or power. Transversal and descriptive studies have
employed all kinds of tests: isometric (Keogh et al., 2009;
Tsai et al., 2004;
Wells et al., 2009;
Wu et al., 2007),
isokinetic (Sell et al., 2007),
isoinertial (Gordon et al., 2009;
Keogh et al., 2009;
Kras and Abendroth-Smith, 2001;
Thompson, 2002;
Wiren, 1968;
Wu et al., 2007),
muscular endurance (Keogh et al., 2009;
Wells et al., 2009),
muscle power (Yoon, 1998),
medicine ball throwing distance (Gordon et al., 2009)
and jump tests (Kras and Abendroth-Smith, 2001;
Wells et al., 2009;
Yoon, 1998).
Studies where a longitudinal
analysis of strength training was performed opted for isometric (Tsai
et al., 2004),
isokinetic (Lephart et al., 2007)
or isoinertial (Doan et al., 2006;
Hetu et al., 1998;
Keogh et al., 2009;
Landford, 1976;
Sthromeyer, 1973;
Thompson and Osness, 2004;
Westcott et al., 1996)
tests, as well as rotational trunk power by throwing a medicine ball with
subsequent qualitative video analysis (Doan et al., 2006;
Hetu et al., 1998).
Equipment used to assess strength consisted mainly of dynamometry (used
in free-weight exercises as well as weight-training machines), isokinetic
machines (Byodex System; Cybex), force platforms, 3D electromagnetic motion
analysis system (trunk rotation), digital video cameras and, in one occasion,
a potentiometer (Yoon, 1998).
Moreover, few of the previously discussed studies (Gordon et al., 2009;
Kras and Abendroth-Smith, 2001;
Wells et al., 2009;
Yoon, 1998)
actually analyzed strength variables which are able to explain performance
in sports training or competition settings.
Most research seems to support the idea that using isometric (constant
angle) or isokinetic tests (constant velocity) to assess dynamic performance
is not adequate since these types of muscle actions usually have a relatively
poor relationship to dynamic athletic performance (Abernethy et al., 1995;
Baker et al., 1994;
Murphy et al., 1995;
Murphy and Wilson, 1996;
Wilson and Murphy, 1996).
Therefore, dynamic actions in isoinertial conditions (constant gravitational
load) together with adequate testing protocols would seem more appropriate
to evaluate muscle strength and power for golf, where the swing is characterized
by high accelerations. However, although there exist large neural and
mechanical differences between isometric and isokinetic tests and functional
movements (Harris et al., 2007),
several studies indicate that the ability to exert maximal isometric force
appears to have some common traits with the ability to generate force
rapidly, at least in sports with high strength demands such as Olympic
weightlifting, football, throwing and track sprint-cycling (Haff et al.,
1997;
McGuigan and Winchester, 2008;
Stone et al., 2003,
2004).
Characteristics
of the participants
The performance level and characteristics of participants may influence
the results of the investigations. With regards to performance represented
by handicap, the samples used in the previously analyzed studies are quite
heterogeneous: studies with high-performance level (HCP < 5) subjects
(Gordon et al., 2009;
Pinter, 1992;
Yoon, 1998),
low-performance level (Fletcher and Hartwell, 2004;
Lephart et al., 2007;
Wiren, 1968;
Wu et al., 2007),
or studies with participants of different handicap (Doan et al., 2006;
Keogh et al., 2009;
Landford, 1976;
Sell et al., 2007;
Thompson and Osness, 2004;
Tsai et al., 2004)
are found. Other studies did not indicate the participants' handicap (Hetu
et al., 1998;
Kras and Abendroth--Smith, 2001;
Thompson, 2002;
Thompson et al., 2007;
Wells et al., 2009;
Westcott et al., 1996).
In addition, while some studies opted for young participants (Doan et
al., 2006;
Kras and Abendroth-Smith, 2001;
Lennon, 1999;
Seiler et al., 2006;
Wu et al., 2007)
or seniors only (Hetu et al., 1998;
Thompson, 2002;
Thompson et al., 2007;
Thompson and Osness, 2004;
Westcott et al., 1996),
other investigations chose samples of varying (22-84 yr) age (Fletcher
and Hartwell, 2004;
Gordon et al., 2009;
Keogh et al., 2009;
Landford, 1976;
Lephart et al., 2007;
Reyes, 2002;
Sell et al., 2007;
Wells et al., 2009;
Wiren, 1968;
Yoon, 1998).
There were even studies where neither age nor gender was indicated (Tsai
et al., 2004)
or where males and females were mixed (Wells et al., 2009).
In the study of Wells et al., 2009
both males (n = 15) and females (n = 9) were included in the same analysis,
thus artificially inflating the correlation between muscle strength and
golf performance variables because although the two groups were high-level
amateur golfers, they were heterogeneous in terms of absolute performance
level. The wide age range sample (17-73 yr) and very different HCP (0-14)
used in the study of Wiren, 1968
facilitates finding correlation between variables but does not guarantee
that within a highly competitive age range (approximately 18-35 yr) such
a correlation exists. Studies in which driving distance was not actually
measured but self-reported by the participants (Sell et al., 2007;
Tsai et al., 2004)
should not be worth considering. The accessibility of the participants
is a factor that must also be taken into account. It is generally problematic
to find a suitable group of elite players, regardless of age. The size
of the sample is another important issue because a larger sample implies
a narrower confidence interval which allows generalizing the
observed correlations to the target population (Hopkins, 2006).
However, in the majority of the reviewed studies sample sizes were too
small to draw sound conclusions about the importance of various expressions
of muscle strength to improve golf swing performance.
Methodological designs have to be carefully considered when attempting
to generalize research results. The sample profiles employed in these
studies are too heterogeneous to allow extrapolation to different populations
(e.g. amateurs vs. professionals, young vs. adults, men vs. women).
Training
design: longitudinal studies
Regarding training methodology, all the investigations were of short duration,
ranging from 4 to 11 weeks, except Lennon, 1999,
with a majority of 8-wk training programs, 2-4 sessions per week, 35-90
minutes per session. Even though the training programs significantly differed
between studies, the strength protocols show some common traits: 2-3 sets
x 10-12 repetitions and/or 2-3 sets x 6-8 repetitions. Some of these programs
included plyometric exercises (Doan et al., 2006;
Fletcher and Hartwell, 2004;
Hetu et al., 1998)
and only one used isometric training (Reyes, 2002).
Although the results of these studies showed significant improvements
in some or all of the strength exercises evaluated, some studies did not
include a control group (Doan et al., 2006;
Hetu et al., 1998;
Jones, 1999;
Wenzel, 1968), or in some cases the information was not disclosed (Lephart
et al., 2007). Of the investigations that used a control group, only
some of them assigned the participants randomly (Fletcher and Hartwell,
2004; Landford, 1976; Lennon, 1999; Sthromeyer, 1973;
Thompson et al., 2007;
Thompson and Osness, 2004).
When a control group is not used, it is difficult to ascertain whether
the observed improvements are actually due to training or to naturally
occurring changes, learning effect between tests or biological maturation
in the case of youngsters. An analysis of the relationship between changes
of these variables could possibly help to overcome the aforementioned
limitations.
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,
Luis Sánchez-Medina3 and Juan J.
González-Badillo3
