Biomechanical correlates of club-head velocity during the golf swing

International Journal of Performance Analysis in Sport 2014, 14, 54-63. Biomechanical correlates of club-head velocity during the golf swing Sinclair J 1, Currigan G 1, Fewtrell DJ 1 and Taylor PJ 2 1 Division of Sport Exercise and Nutritional Sciences, University of Central Lancashire 2 School of Psychology, University of Central Lancashire Abstract Golfers are able to attain a competitive advantage when they are able to achieve long hitting distances from the tee. Club-head velocity is perhaps the most commonly reported kinematic variable in the golfing scientific literature. This study aimed to identify 3-D kinematic aspects of the golf swing linked to the generation of club-head velocity using regression analyses. Maximal golf swings were obtained from fifty golfers using an eight camera motion capture system operating at 500 Hz. Full body threedimensional kinematics were obtained. Multiple regression modelling was used to identify the discrete 3-D kinematic parameters associated with the development of club-head velocity. Two biomechanical parameters; sagittal plane wrist velocity and peak transverse plane torso rotation (Adj R 2 =0.58, p 0.01) were obtained as significant predictors of club-head velocity. The findings from this study therefore suggest these parameters are the strongest contributors to ball velocity and potentially overall driving performance. It is conceivable based on these observations, that golfers may benefit from exposure to coaching and conditioning techniques geared towards the improvement of these parameters in order to improve their driving distance. Keywords: 1. Introduction Golfers are able to attain a competitive advantage when they are able to achieve long hitting distances from the tee (Joyce et al., 2012). Therefore, improved driving performance is of importance to most golfers, irrespective of skill level. Club-head velocity is perhaps the most commonly reported kinematic variable in the golfing scientific literature. It is utilized as the sole measure of performance, under the logical assumption that a higher club-head velocity will produce a greater ball release velocity and thus greater distance (Gordon et al., 2009; Keogh et al., 2009; Sprigings & Neal, 2000). Biomechanical analyses through different research modalities have been used to investigate the key contributors to club-head velocity. Club-head velocity has been shown to be related to physical and anthropometric characteristics such as trunk 54

flexibility and height (Kawashima et al., 2003; Fradkin et al., 2004 Doan et al., 2006; Wells et al., 2009). Theoretical and mathematical modelling approaches have been formulated to describe characteristics of the golf swing from a mechanical standpoint (Penner, 2003). The influence of variables such as wrist hinge angle, club release angle, and moments applied by the shoulders and wrists throughout the swing were assessed by altering a double pendulum model which simulated a real golf swing (Miura, 2001; Penner, 2003). Furthermore, previous kinematic investigations have shown that variables including and increased angle of the backswing (Reyes & Rittendorf, 1998), delayed club release (Pickering & Vickers, 1999), greater rotational torque applied at the arms centre of rotation (Jorgensen, 1994), have all been associated with increases in club-head velocity. The separation angle between the pelvis and torso segments orientation in the transverse plane is referred as the X-factor and is a reflection of sequential trunk rotation. This angle of separation has been shown to be larger in professional (Cheetham, Martin, & Mottram, 2000) and low-handicap golfers (Watanabe, Kuroki, Hokari, & Nishizawa, 1998) in comparison to less skilled players. Chu et al., (2010) were the first to use full body kinematic modelling and were able to determine that 44 74% of the variance in club-head velocity could be explained using biomechanical parameters of X-Factor separation angle, trunk forward and lateral tilt, and weight shift magnitude during the swing. But whilst their results were determined from a large and relatively skilled cohort their trunk rotational measures were derived from transverse plane projections which are prone to non-sagittal overestimation in comparison to more contemporary euler methods in which the torso is considered a rigid body (Wheat et al., 2007; Horan et al., 2010). Despite extensive golf specific biomechanical data collection and research, there is a clear paucity of published communications that have comprehensively evaluated the relative importance of 3-D biomechanical parameters and their role in maximizing clubhead velocity. Therefore the aim of the current investigation was to determine the important technical aspects of the golf swing pertinent to the generation of club-head velocity using 3-D kinematic modelling and multiple regression techniques. This study tests the hypothesis that 3-D kinematic parameters will serve as significant predictors of club-head velocity during the full golf swing. 2. Methods 2.1. Participants Fifty participants (thirty-one males and nineteen females) volunteered to take part in this investigation. The mean characteristics of the participants were; age 30.44 ± 6.13 years, height 177.11 ± 6.21 cm, body mass 73.19 ± 8.33 kg and R&A handicap 11.75 ± 1.66. The procedure utilized for this investigation was approved by the University of Central Lancashire, School of Sport Tourism and Outdoors, ethical committee. All participants provided written informed consent in accordance with the principles outlined in the declaration of Helsinki. 55

2.2. Procedure Kinematic data was captured at 500 Hz via an eight camera motion analysis system (Qualisys Medical AB, Goteburg, Sweden). Calibration of the system was performed before each data collection session. Only calibrations which produced average residuals of less than 0.85 mm for each camera for a 750.5 mm wand length and points above 4000 in all cameras were accepted prior to data collection in accordance with Sinclair et al., (2013). The marker set used for the study was based on the calibrated anatomical systems technique (CAST) (Cappozzo et al., (1995). The thorax, pelvis, feet, shanks, thighs, upper arms, forearms and hands were defined. Retro-reflective markers were attached bilaterally to the calcaneus, 1st and 5th metatarsal heads, medial and lateral malleoli, medial and lateral epicondyle of the femur, greater trochanter anterior (ASIS) and posterior (PSIS) superior iliac spines, acromion process, medial and lateral humeral epicondyles, radius, ulna and heads of the 2 nd and 5 th metacarpals. Rigid tracking clusters were positioned bilaterally onto the shank, thigh, upper arm and forearms. Each rigid cluster comprised four 19mm diameter spherical reflective markers mounted to a thin sheath of lightweight carbon fibre with length to width ratios in accordance with Cappozzo et al., (1997). A static trial was conducted with the participant in the anatomical position in order for the positions of the anatomical markers to be referenced in relation to the tracking clusters, following which they were removed (Figure 1). 56

Figure 1: Anatomical model and marker set used to quantify full body kinematics. Each participant was instructed to perform their typical warm-up prior to the commencement of data collection. Data collection consisted of each participant performing full golf swings using a standard driver (Taylormade R1, 9⁰ loft) with a stiff-flex graphite shaft (Grafalloy Prolaunch blue). Each participant performed 10 shots from an artificial turf tee box positioned in the middle of the laboratory. 2.3. Data Processing Dynamic movement trials were processed using Qualisys Track Manager in order to label anatomical and tracking markers, following which they were exported as C3D files. Key elements of the swing that were defined to allow time normalization of the kinematic waveforms were set-up and ball impact which was delineated via the motion capture system using retroreflective tape which covered the golf ball and retroreflective 57

markers that were screwed into the driver head. 3-D Kinematic parameters were quantified using Visual 3-D (C-Motion Inc, Germantown, MD, USA) and filtered at 25 Hz using a zero-lag low pass Butterworth 4th order filter. Angles were created using an XYZ cardan sequence referenced to co-ordinate systems about the proximal end of the segment, where X =sagittal; Y = coronal and Z = transverse plane rotations, the exception to this was the shoulder joint which was quantified using a ZYZ sequence of rotations in accordance with Wu et al., (2005). 2.4. Statistical analyses Multiple regression analyses with clubhead velocity as the criterion and the 3-D kinematic parameters as independent/ predictor variables were carried out using a forward stepwise procedure with significance accepted at the p 0.05 level. The independent variables were examined for co-linearity prior to entry into the regression model using a Pearson s correlation coefficient matrix and those exhibiting high colinearity R 0.7 were removed. All statistical procedures were conducted using SPSS 21.0 (SPSS Inc, Chicago, USA). 3. Results 3.1. Club head velocity and multiple regression analysis Figure 2 presents the mean ± standard deviation kinematic parameters from the torso and wrist in the transverse and sagittal planes. The results revealed a mean ± standard deviation club-head velocity of 151.11 ± 16.98 km.h -1. The overall regression model was significant and yielded an Adj R 2 of 0.58, p 0.01. Two biomechanical parameters, peak transverse plane torso rotation (B=0.62, t=4.91) Adj R 2 =0.37, p 0.01 and sagittal plane wrist extension velocity at ball impact (B=0.47, t=3.67) Adj R 2 =0.21, p 0.01 were obtained as a significant predictors of clubhead velocity. 58

Figure 2: Kinematic parameters linked to the generation of club-head velocity (a = transverse plane torso rotation and b = sagittal plane wrist angular velocity) (LR =left rotation and EXT = extension). 59

4. Discussion The aim of the current investigation was to determine the important technical aspects of the golf swing pertinent to the generation of club-head velocity using 3-D kinematic modelling. This represents the first study to use full body 3-D kinematics to determine the biomechanical predictors of club-head velocity. In support of the hypothesis it was shown that 3-D kinematic parameters served to significantly predict club-head velocity. Most importantly, the regression model revealed that peak transverse plane torso rotation and sagittal plane wrist velocity at ball impact were most strongly related to the generation of club-head velocity. This concurs with the proposition of Chu et al., (2010) who suggest that kinematic measures are important in the development of club-head speed. That wrist angular velocity at ball contact was significantly related to the generation of club-head velocity is interesting as anecdotal coaching literature has highlighted the importance of the un-cocking the wrists in creating high club-head velocity at impact. The linear velocity of the club-head which ultimately governs the resultant driving distance is strongly influenced by the angular velocity of the right wrist in the sagittal plane (Sprigings & Neal, 2000). The linear velocity of the club-head is proportional to the product of the angular velocity and radius rotation of the shaft thus the significant relationship between wrist angular velocity and club-head velocity appears to be a rational one. Furthermore, that the peak transverse plane torso rotation was revealed as a significant predictor of club-head velocity is intuitive and concurs with current propositions from the literature. The transverse plane separation between torso and pelvis which is referred to as the X-factor has been examined extensively in biomechanical analyses of the golf swing (Cheetham et al., 2000; Chu et al., 2010; Joyce et al., 2012). The sequence of the X-factor movement results in the musculature surrounding the pelvis and torso receiving an eccentric stretch before releasing into a concentric action in the early downswing. This mechanism is known commonly as the stretch-shorten cycle (Cole & Grimshaw, 2009). Actively stretching the musculature prior to its primary concentric action facilitates much more positive work than concentric motions alone (Enoka, 1994). Therefore based on the observations of the current investigations it appears that in order to maximize club-head velocity, it is important to maximize the transverse plane separation between torso and pelvic at the top of the backswing (Chu et al., 2010; Joyce et al., 2012). The findings from the current study may permit training modifications to be made with the aim of increasing club-head velocity during the golf swing. It is commonly believed that sport specific strength and conditioning programmes are able to improve performance in golf. Therefore, based on the observations of the current investigation a conditioning program that emphasises the development of strength and power in the forearm and wrist musculature would allow golfers to rotate the wrists at a higher velocity, thus facilitating the generation of greater club-head velocity. Furthermore, it is recommended that golfers also incorporate a flexibility training regimen of the torso 60

into their training regime. It has been shown that flexibility training has provided sizeable increases in club-head velocity in golfers of all levels. Although the regression model in the current investigation was statistically significant, there remains a large proportion of variance (42 %) that could not be attributed to the discrete kinematic entered into the multiple regression model. Therefore, it can be concluded that the current investigation could not account for all of the mechanical factors that contribute to club-head velocity during the golf swing. Whilst the current study performed a comprehensive discrete 3-D kinematic analysis of the golf swing and attempted to relate these parameters to the generation of club-head velocity, there was not any consideration of the kinetic of electromyographical (EMG) potentials that may also be related to club-head velocity transmission. Therefore it is recommended that future analyses attempting to relate biomechanical variables to driving performance in golf consider in greater detail the contribution of kinetic and EMG parameters. A possible limitation of the current examination is that it was undertaken in laboratory conditions. Whilst laboratory based studies are able to standardise the testing conditions, their ecological validity is compromised. This emphasis on laboratory-based studies may change with recent advances in technology allowing comparable levels of analysis to be conducted on the golf course (Neal, Lumsden, Holland, & Mason, 2007), leading to greater ecological validity of these studies. In addition, although club-head velocity has been considered as the criterion variable in a number of biomechanical analyses in golf, there is currently a clear paucity of research examining the parameters associated with accuracy driving during the golf swing. Anecdotal and scientific evidence suggests that there is a trade-off between the generation of club-head velocity and the likelihood of the drive landing in the desired area. Whilst club-head velocity and the driving distance it is associated with has been linked to performance in golf (Belkin et al., 1994; Davidson & Templin, 1986; Jones, 1990), the accuracy of the drive is clearly also important as fairways hit have been shown to be pertinent to good scoring (Belkin, Gansneder, Pickens, Rotella, & Striegel, 1994; Dorsel & Rotunda, 2001). Given the clear paucity of published work investigating the mechanics of accurate driving it is recommended that future investigations consider the discrete biomechanical parameters linked to accurate golf driving. In conclusion this study provides new evidence regarding the discrete 3-D kinematic variables linked to the generation of club-head velocity during the golf swing. The current investigation documents that peak transverse plane torso rotation and sagittal plane wrist velocity at ball impact are most pertinent to the development of club-head velocity. It is recommended that practice and training regimens be modified towards increasing these measures for golfers seeking to improve their driving performance. 61

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