Introduction
Golf has traditionally been viewed as a skill-based sport in which the continual refinement of ball striking and putting skills is emphasised over the development of kinanthropometric (anthropometric and physical fitness) qualities. This is somewhat in contrast to team sports such as Australian rules football (26 27
The ability to generate high linear clubhead velocities (and hence achieve large horizontal ball displacements) has long been thought crucial for golf success (10 r = 0.95) (19 r = 0.41-0.88) (20 13,18,28
According to Newtonian mechanics, linear velocity is a product of angular velocity and the length of the lever, in this case the arm-club system (22 22
The angular impulse-momentum relationship states that angular velocity is proportional to the summation of joint torques (resultant torque) produced by the golfer. Although the resultant golf swing torque is dependent on many factors including the magnitude and direction of the ground reaction force (2,41 37,40 2,37,40 3 3 36,42 23,35 30 13,18,28
While resistance-training appears able to improve clubhead velocity by increasing the resultant muscular torque, the development of flexibility (particularly around the shoulder, trunk, and/or hip joints) has traditionally been emphasized in golf training. The rationale for this emphasis has been that an increase in the range of motion (ROM) in these areas would allow a longer backswing, which then gives the golfer more time to develop high levels of angular velocity (9,44 38,40
Therefore, the purpose of this study was to determine whether a number of selected kinanthropometric variables (many of relevance to the laws and preferences in the Wiren (44
Methods
Experimental Approach to the Problem
The present study used a cross-sectional approach to examine the relationship between a number of kinanthropometric (anthropometry, flexibility, muscular strength, and endurance) measures to golf clubhead velocity in LHG and HHG golfers. Specifically, correlational and between-group analysis of variance analyses were conducted to examine this relationship.
Subjects
A total of 10 male LHG (age 22.9 ± 3.4 years; height 1.80 ± 0.07 m; mass 76.8 ± 8.8 kg; handicap: 0.3 ± 0.5) and 10 male HHG (age 27.8 ± 7.8 years; height 1.77 ± 0.07 m; mass 73.5 ± 11.8 kg; handicap 20.3 ± 2.4) gave informed consent to participate in this study. These groups were balanced so that no significant intergroup differences were observed for age, height, or body mass (p = 0.087-0.484).
All participants were right-handed golfers, had played golf for at least 2 years, and were members of golf clubs. Over recent weeks, each golfer was currently averaging at least 3 hours of golf practice and at least one full round (18 holes) of golf per week. Approximately half of the golfers in each group had been participating in a regular gym program for 1 year or more, with the emphasis of these programs generally being on the development of core stability, muscular endurance, flexibility, and general (overall body) strengthening. Due to their limited resistance training history, only a few of the golfers had regularly performed any power, (e.g. plyometric, weightlifting, or medicine ball throws) or golf-specific rotational exercises (e.g., golf swing-specific cable woodchop [GSCWC] or resisted golf swings) previously in training. For those golfers with a coach or conditioner, no more than two golfers in either group used the services of the same professional. For the purposes of this study, LHG were defined as either professionals (members of the New Zealand Professional Golfers Association) or amateurs who had a handicap of 1 or less. The HHG were all amateurs and had a handicap between 18 and 25. Ethical approval was obtained for all testing procedures from the Auckland University of Technology Ethics Committee.
Procedures
Testing was conducted in early to mid-spring so that all golfers had sufficient practice and/or tournament play in the month(s) prior to testing. All participants were required to attend two testing sessions. The first session involved assessment of the players' kinanthropometric profile, with the order of tests being anthropometry, flexibility, then muscular strength and endurance. All tests were conducted at a similar time of day to ensure consistency of measurement between the LHG and HHG groups. Measures of golf performance (clubhead velocity and accuracy) were obtained during the second testing session, which was conducted approximately 1 week after the kinanthropometric testing session.
Anthropometry
Anthropometric testing used International Society for the Advancement of Kinanthropometry (ISAK) protocols (33
Stretched stature was measured without shoes using a standard wall mounted stadiometer to the nearest 0.1 cm. Body mass was measured to the nearest 0.1 kg, using a calibrated SECA Atrax 770 electronic scale (Seca, Hamburg, Germany). Skinfolds were measured on the right side of the body using a Slim Guide caliper to the nearest 0.5 mm. Arm segment lengths and shoulder breadth were measured using a Siber-Hegner anthropometer to the nearest 1 mm. Girths of the chest and relaxed upper arm were measured using a Lufkin W606PM flexible steel tape to the nearest 1 mm. Each skinfold, length, breadth, and girth was measured three times with the median result used in data analyses. All anthropometric measures were highly reliable, with the intraclass correlation coefficients (ICC) being: skinfolds (ICC = 0.87-0.99), lengths (ICC = 0.89-0.94), bone breadth (ICC = 0.97) and girths (ICC = 0.86-0.90). Further, the technical error of measurement (TEM) for all anthropometric measures was within ISAK requirements of <5% for skinfolds and 1% for other measurements.
A number of derived anthropometric measures were also calculated. Body mass index (BMI) was equal to body mass (kg) divided by height (m) squared. Body density (BDM4) was calculated using the sum of four skinfolds (Σ4SF: triceps, subscapular, supraspinale and medial calf) in the equation: BDM4 = 1.09736 − 0.00068(Σ4SF) (45 39
Flexibility
Trunk rotation, wrist abduction, wrist adduction, and hip internal and external rotation flexibility was assessed using active ROM tests with methods sharing many similarities to Doan et al. (13
The active trunk rotation test was performed in a similar fashion to that of Doan et al. (13
For the active wrist abduction and adduction tests, markers were placed on the metacarpal-phalangeal joint of the third digit of the back (right) hand, the center of the wrist joint between the styloid processes of the radius and ulna, and the medial aspect of the distal portion of the biceps brachii tendon. Golfers knelt on the ground with their right forearm placed on the stadiometer box with the hand in a supinated position, the elbow directly under the shoulder so to create a 90° elbow angle. From this position, the golfer abducted the wrist as far as possible and held that position for 3 seconds, before moving through the neutral position to the maximum wrist adduction position, with this position also held for 3 seconds.
For the hip internal and external rotation tests, markers were placed on the center of the tibial tuberosity of each leg and between the midpoint of the lateral and medial malleoli. Golfers were seated on a plinth (high enough so that the feet could not touch the ground) with their hips and knees bent to 90°. The centers of the knee joints were aligned with the edge of the plinth and the hips and knees were stabilized by tight belts to prevent unwanted movement during the test. A box was also placed behind the golfer so they could not extend or flex their back while performing the movement. The golfers internally rotated their bent leg as far as possible and held this position for 3 seconds, then moved back through the neutral position and externally rotated the same leg as far as possible, and held this position for 3 seconds before moving back to the neutral position. The same movements were completed on the opposite leg.
Joint markers from each of the flexibility tests were digitized using Silicon Coach Professional (Dunedin, New Zealand) to enable calculation of joint ROM (12
Muscular Strength and Endurance
Prior to performing the muscular strength and endurance tests, the golfers completed a standard warm-up of 5 minutes of cycling on a TRUE Z8 stationary bicycle, a series of upper and lower body stretches, and a familiarization set (∼20-40% 1 repetition maximum [RM]) of each of the three muscular strength (GSCWC, bench press, and hack squat) and one endurance (isometric prone hold) tests. Each strength and endurance test was separated by a 2-minute rest.
The muscular strength and endurance tests were selected after reviewing the golf conditioning (13,18,28 3,35,36,42 13,18,28 13 18 28
The three general exercises (bench press, hack squat, and isometric prone) were chosen on the basis of the following factors: a) that they (or very similar derivatives) had been included in training studies that had shown significant improvements in clubhead velocity/ball displacement (13,18,28 3,35,36 16,17 8,9
All golfers completed the series of tests in the same order. For the GSCWC, bench press, and hack squat exercises, the 1RM was estimated from a submaximal (3-6 RM) load using the equation of Brzycki (6 X , where X is the number of repetitions performed. If more than 6 repetitions were performed, the golfer rested for 2 minutes and then performed the same exercise with a heavier load that would likely result in failure in 3-6 repetitions.
The GSCWC test is a rotational exercise that is very similar to the golf swing in terms of posture, range of motion, intended velocity, direction of force (torque) application, and coordination patterns (8 Figure 1 ). In keeping with the mechanics of the golf swing and the kinetic-link principle (22
Figure 1: Golfer performing the golf swing-specific cable woodchop exercise. a) Starting position. b) Mid position. c) Finishing position.
For the bench press test, golfers lay in a supine position on an exercise bench. At all times, the golfers were required to keep their buttocks and shoulders in contact with the bench and their feet flat on the floor. The bar was gripped with an overhand grip ∼1.5 times shoulder width apart, so that when the elbows were bent to 90°, the hands were directly above the elbows. The barbell was lifted off the rack, lowered until it touched the chest, and then pressed back up until the elbows were fully extended.
When performing the hack squat test, the golfers positioned themselves with their back against the padded surface, shoulders wedged beneath the yokes attached to the backrest, feet placed shoulder width apart on the footplate. The golfers then flexed their knees to 90° before extending the knees back to the starting position. During the movement, the heels were required to maintain contact with the footplate and the gluteals, shoulders, and head with the backrest.
The isometric prone hold required the golfers to assume a prone position on the floor with the only contact between the floor being the feet and the forearms. The shoulder was in a flexed position, with the elbows bent to 90° and positioned directly under the shoulders (see Figure 2 ). All golfers were required to hold this position for as long as possible, with the time recorded using a stopwatch. The test was terminated when the first of two criteria was met. The first criterion was when the golfer suddenly collapsed to the floor. The second was when the golfer's hips (anterior superior iliac spine) dropped or lifted more than 2 cm from the starting (neutral spine) position. For the second criteria, the golfer was given an initial warning on the first occurrence; when there was a repeat infringement, the test was terminated.
Figure 2: Golfer performing the isometric prone hold exercise.
Golf Swing Performance
Golf swing testing was conducted at Auckland University of Technology's Golf Swing Clinic, which has eight bays (each ∼20 m long) with an artificial grass Astroturf surface and netting. Prior to performing the golf swing testing, each golfer completed a semistandardized warm-up, which consisted of ∼10-15 minutes of progressively more intense golf swings and stretching. During this warm-up, the subjects were asked to aim at the target to familiarize themselves with the experimental setup. The target, which was positioned 15 m in front of the golfer, was 1 m wide and 1.4 m high, with the bottom of the target 4.2 m above the ground to approximate the expected trajectory of the 5-iron.
After completing their warm-up, each golfer performed 10 swings for maximum velocity and accuracy with their own 5-iron golf club. The 5-iron was chosen over a driver for the following reasons: a) to reduce the ball velocity and hence the chance for the ball to pass through the net (as this had occurred when some LHG used a driver in pilot testing); b) to make it easier to determine the accuracy of the shot; and c) to more easily conduct a 50-Hz video analysis of the golf swing (5 11,15
Maximum clubhead velocity for each golf swing was measured using a Stalker Professional Sports radar gun (Applied Concepts, Plano, Texas, USA) operating at a frequency of 34.7 GHz (29 29 −1 ) for activities up to 300 mph (∼133 m·s−1 ). The intertrial reliability of the players' clubhead velocity was high as indicated by the coefficient of variation (CV) and intraclass correlation coefficients (CV = 3.1% and ICC = 0.88).
Statistical Analyses
Standard descriptive statistics (mean, SD , and range) were calculated for the golf performance (clubhead velocity and accuracy), anthropometric, flexibility (ROM), and muscular strength and endurance test variables. Normality of data (for each group) was assessed using the critical appraisal approach (34 SD test (2SD < mean), b) Shapiro-Wilks statistics (p > 0.05), c) skewness and kurtosis statistics (within 1), and d) skewness or kurtosis/SE (within 1.96). Individual data that breached these criterions were excluded from further analysis.
Significant intergroup differences in these measures were assessed using a one-way analysis of variance. Cohen effect sizes (d ) were also calculated in order to quantify the magnitude of the between-group differences. In accordance with the revised effect size (ES) magnitudes of Drinkwater et al. (12
Relationships between clubhead velocity and the dependent variables for the entire sample of 20 golfers were determined using Spearman's rank correlation coefficients. This test was chosen over the more common and powerful Pearson product moment correlation because the significant between-group differences in a number of the dependent variables made the total group data bimodal in nature. The bimodality of this data violates the assumptions of normality underlying the Pearson product moment correlation (4 p < 0.01 to account for the relatively high number of between-group comparisons.
Power analyses were conducted to determine the number of subjects required in this study. According to Hopkins (20 r = 0.5 can be considered high and equates to an effect size of 1.2. Twenty-two subjects in total would be required for a correlation coefficient of r = 0.5 to be significant, with 80% power and a risk of type I error of 5%. Using the methods of Hopkins (19 2
Results
Compared to HHG, LHG generated significantly greater (12%) clubhead velocity and were significantly more accurate as evidenced by their ability to hit the target more than twice as often (Table 1 ). Low-handicap golfers also had significantly greater GSCWC (28%) strength than the HHG (Table 1 ). Although not statistically significant, LHG also tended to have significantly greater (5%) acromiale-radiale (upper arm) and (4%) acromiale-stylion (total arm) lengths and (30%) bench press strength, but less (24%) right hip internal rotation than HHG (ES = 0.98-1.12, p = 0.023-0.042). No statistically significant intergroup differences were observed for any of the other kinanthropometric variables.
Table 1: Golf swing performance, anthropometry, flexibility (range of motion), and predicted 1RM muscular strength measures of low handicap and high handicap golfers, and correlations between the selected variables and maximum clubhead velocity.
Significant correlations were observed between clubhead velocity and that of handicap, target accuracy and GSCWC strength (Table 1 ). Although not statistically significant, clubhead velocity also tended to be positively correlated to bench press and hack squat strength and to acromiale-radiale and acromiale-stylion length (r = 0.45-0.52, p = 0.019-0.045). No significant correlation was observed between clubhead velocity and any ROM variable.
Discussion
The purpose of the present study was to determine if selected kinanthropometric variables were correlated to clubhead velocity and if these variables could distinguish between LHG and HHG. Results were somewhat consistent with the initial hypotheses, with a small number of kinanthropometric variables significantly (or tending to be) correlated to clubhead velocity and significantly (or tending to be) different between LHG and HHG. Such results suggest that a golfer's performance may be partially related to their kinanthropometric profile.
As hypothesized, the LHG (37.6 ± 1.0 m·s−1 ) had greater 5-iron clubhead velocity than the HHG (33.0 ± 1.8 m·s−1 ). These clubhead velocity values appeared similar to other studies involving a 5-iron (∼34-41 m·s−1 ) (15,24 −1 ) (12,14,17 32
It was apparent that no anthropometric variables were significantly correlated to clubhead velocity and that no significant between-group anthropometric differences existed. Such results may suggest that anthropometry has little influence on clubhead velocity and that the anthropometric profile of LHG and HHG was quite similar. To our knowledge, Kawashima et al. (25 25 r = 0.450-0.453) approached significance (0.01 < p < 0.05). The results of this study and that of Kawashima and colleagues (25 26
Consistent with previous studies (13,24 24 13,18,28
While somewhat speculative, the trend for the LHG to have reduced internal hip rotation ROM may reflect a between-group difference in hip and shoulder rotation (turn) during the backswing and early downswing. Previous research has shown that the greater the relative rotation of the trunk compared to the hips at the top of the backswing or early in the downswing (referred to as the X-factor and X-factor stretch, respectively), the greater the clubhead velocity and ball displacement (7,31 7,31
Results of the present study indicated that GSCWC strength was significantly greater in LHG than HHG and significantly correlated to clubhead velocity. Trends were also evident where bench press strength may have been greater in LHG than HHG (moderate effect size) and significantly correlated (r = 0.500) to clubhead velocity (0.01 < p < 0.05). Such between-group differences in strength were observed even though the LHG's tendency for longer arms would have placed them at a mechanical disadvantage in these exercises compared to the HHG.
The fact that GSCWC strength was more highly related to clubhead velocity than the other muscular strength and endurance tests was consistent with the specificity principle (1,43 8 13,18,28
With respect to the between-group differences in clubhead velocity seen in the present study, it is however unclear if it was the LHG's greater GSCWC strength (and hence ability to generate angular velocity) or arm (lever) length that contributed more to their significantly greater clubhead velocity than the HHG. Regardless, golfers with shorter arms need to generate greater joint angular velocities than players with longer arms in order to achieve comparable clubhead velocities and hence ball displacements (22
High levels of trunk muscular endurance have been proposed to stabilize the spine during the swing, thereby allowing the efficient transfer of ground reaction forces through the trunk and arms to the clubhead (8,9 16,17 r = 0.434). Although not definitive, the results of the present and previous studies (13,16-18
There were a number of limitations within the present study. These include the inability to recruit sufficient subjects to obtain 80% power for all dependent measures. Therefore, some variables that should have been significantly different between groups or correlated to clubhead velocity may not have obtained statistical significance. The relatively low sample size (n = 20) would also mean that the confidence limits of the correlations would be somewhat broad. Thus, a larger sample (n > 50) of golfers would need to be tested to reduce the uncertainty in the true value of the correlations reported in this study. In addition, the present study assessed golf performance with one club and two groups of male golfers of relatively narrow handicap ranges, age, and anthropometric profiles. Thus, further research is required to confirm that similar results would be found when using other clubs (e.g., a driver) and for a different sample, such as female golfers or male golfers of different standards, age, and/or anthropometric profile to that assessed in the present study.
Practical Applications
Results of this study suggest that LHG and HHG have a relatively similar kinanthropometric profile. However, LHG had significantly greater GSCWC strength and trends for greater bench press strength and longer arms than HHG. While GSCWC strength was the only kinanthropometric variable that was statistically correlated to clubhead velocity, bench press and hack squat strength as well as upper arm and total arm length also tended to be correlated to clubhead velocity. These results suggest that the kinanthropometric profile of LHG may confer a competitive advantage and contribute to their greater clubhead velocity. Talent identification programs may wish to select players with higher GSCWC and/or bench press strength as well as longer arms, while conditioners may seek to further improve trunk rotation strength and power via exercises like the GSCWC and/or other plyometric rotational exercises. These conditioning programs should probably not overemphasize the development of muscular hypertrophy because excessive hypertrophy may negatively affect performance by limiting joint ROM and/or by increasing the moment of inertia of particular body segments. The astute conditioner should also include preventative (prehabilitation) exercises that minimize the risk of injury to at-risk areas, such as the lower back and shoulder.
Acknowledgments
We thank Sam Aickin for assisting with data collection and analysis and the subjects who gave up their time for this project. This project was supported by a Faculty of Health and Environmental Sciences, Auckland University of Technology Contestable Research Grant.
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