Young-Hoo Kwon, Chris Como, Ki Hoon Han, Sangwoo Lee, & Kunal Singhal Biomechanics Laboratory, Texas Woman’s University, Denton, TX Decomposition of the Clubhead Velocity: Assessment of the Contributions of the Joint/Segment Motions in Golf Drives 6th World Scientific Congress of Golf, Phoenix, AZ

Planar Double-Pendulum Model Triple-pendulum model X-Factor Stretch-Shortening Cycle (Cochran & Stobbs, 1968; Hume et al., 2005; Hellstrom, 2009)

Planarity & Functional SP Motion Planes L Shoulder R Shoulder MD R Elbow MF L Hand FSP FSP (Kwon et al., 2012)

New Double-Pendulum Model Hand Path Determined by: Trunk motion & Arm motions Projected Clubhead New Hub Trunk Motion: Flexion/extension Lateral flexion Rotation Elevation/depression Projected Hand Arm Motions: Shoulder motions Elbow motions

New Kinematic Sequence: Joint Angular Velocities Meaningfulness of the trunk rotation and the X-factor?

X-Factor Studies Trends: Issues: Comparison among different skill levels (Cheetham et al. 2000; Zheng et al., 2007; Cole & Grimshaw, 2009) Comparison among different ball velocity groups (Myers et al., 2007) Comparison among different effort levels (Meister et al., 2011) Correlation/regression (Myers et al., 2007; Chu et al., 2010) Training effects (Lephart et al., 2007) Methodology (Joyce et al., 2010) *p < 0.05 Issues: ANOVA/correlation/regression with heterogenous samples No direct relationship between CH velocity and X-factor Influence of the planar swing model / stretch-shorting cycle Projected to the horizontal plane

Purposes To assess the contributions of the joint/segment motions to the clubhead velocity: Homogenous sample Normalized CH velocity Direct relationship between the CH velocity and the trunk motion To assess the relationship between the X-factor parameters and the CH velocity: Projected to the functional swing plane Homogenous sample Normalized CH velocity

Participants 18 Male Skilled Golfers: Clubhead Velocity: Recruited from North Texas (Dallas) area Handicap: -0.6 ± 2.1 Height: 1.81 ± 0.05 m Mass: 82.6 ± 10.4 kg Clubhead Velocity: 45.48 ± 2.85 m/s (102.3 ± 6.4 mph; CV = 6.3%) 25.21 ± 1.82 BH/s (CV = 7.2%)

Data Collection Motion Capture: Laboratory Study: 10-camera VICON system (Centennial, CO) Captured at 250 Hz ‘TWUGolfer’ marker set (65 markers) 2 AMTI force plates (250 Hz) 4 different types of trials (ball plate, club, static posture, & motion trials) captured Laboratory Study: Wiffle balls Ball mat 5 driving trials per golfer collected

Data Processing ‘TWUGolfer’ Body Model: Data Processing: 89 points 13 joints / 24 computed points 18 bodies / 6 additional reference frames Data Processing: C3D importing Kwon3D (Visol, Seoul, Korea) Cutoff frequency: 20/10 Hz Interpolated to 2,000 Hz

Events TB ED MD BI MF Top of BS Early DS Mid DS Ball Impact Mid FT

Functional Swing Plane (FSP) FSP (Kwon et al., 2012): Plane formed by the clubhead trajectory (MD to MF) Projected trajectory Moving FSP Reference Frame: Instantaneous rotation centers & arms Normal, tangential, & radial axis n ro X-Factor Computation: Shoulder & hip lines Projected to the FSP frame

Decomposition of CH Velocity Wrist (2 + 1 DOFs) Elbow (1) 1 Shoulder Joint (3) A 4 Mid-Shoulder (1) D 5 C L4/L5 (3) E B Pelvis Rotation (3) 2 3 6 F 7 Mid-Hip Translation Time Function: Max contribution Contribution at BI Contribution

Tangential Velocity Contribution 100% TB: 0% ED: 67.0% 46.9% MD: 86.9% 16.8% BI: 100% 19.2% 15.7% (1) (12) (5) 18.5%

Velocity Contribution vs. Max CH Velocity (p < 0.05) r = 0.724 r = 0.539 r = 0.501 r = -0.475 (1) (3)

X-Factor Parameters

X-Factor Parameters X-Factor Stretch 1.5 ± 2.2 deg

X-Factor Parameters CV = (15, 79, 18)% CV = (21, 25, 17)% vs. Max CH Velocity r = -0.461* (*p < 0.05) r = -0.486* r = -0.568*

Discussion Velocity Contribution: Velocity Decomposition: Wrist motion: the main source of the CH velocity Pelvis motion: larger contributions than the trunk motion Wrist & pelvis contributions: correlated to the max CH velocity Trunk motion: no notable contribution / correlation to the max CH velocity Velocity Decomposition: Decomposed velocities  causal relationships 3-D modeling studies needed: to establish the causal relationship

Discussion (cont.) X-Factor: Not the X-factor but the hip & shoulder parameters were correlated to the max CH velocity. Direct relationship between max CH velocity and X-factor is questionable. Inter-group difference in X-factor may mean fundamental differences in swing style. The X-factor could be an indicator of the golfer’s skill level.

Discussion (cont.) Golf swing:  a planar motion around a hub (Cochran & Stobbs, 1968) Planar perspective, X-factor, & SSC: Popular menus Time to reassess their meaningfulness Trunk & arms: work together to achieve a planar CH motion in the delivery zone Future studies: trunk-arm coordination

Conclusion Velocity decomposition revealed that contribution of the trunk motion to the max CH velocity was minor. Not the X-factor, but the hip and shoulder line position/ROM showed significant correlations to the max CH velocity. The link between the X-factor/stretch-shortening cycle perspective and CH velocity generation is questionable. Future studies need to focus on hip and shoulder line position/ROM vs. downswing motion patterns.

Thank you for your attention!

Trial Types Static Posture Motion Trial Processed Motion Trial Club Ball Plate

Kinematic Chain Analysis CH Velocity: 1 A 4 D 5 C E B 2 3 6 F 7 Relative Velocity of CH to Wrist:

Segment Perspective: Joint Perspective: 1 A 4 D 5 C E B 3 6 2 F 7 1 A

Decomposition of CH Velocity Wrist (2 + 1 DOFs) Elbow (1) 1 Shoulder Joint (3) A 4 Mid-Shoulder (1) D 5 C L4/L5 (3) E B Pelvis Rotation (3) 2 3 6 F 7 Mid-Hip Translation Time Function: Max contribution Contribution at BI Contribution

Normal Velocity Contribution Up Down

Radial Velocity Contribution Toward

Golf Performance Factors Goal: Accuracy & consistency in distance & direction Maximization of the distance Impact Conditions: Motion of the clubhead (velocity) Orientation of the clubface at impact Location of impact on the clubface Distance: function of the CH velocity at impact

Motion Planes

X-Factor Studies Study Methods Results Cheetham et al. (2000) 10 skilled 9 less skilled ( 15) Skilled > less skilled (max) Zheng et al. (2007) 18 professional (0) 18 low HC (3.22) 18 mid HC (12.5) 18 high HC (21.3) Pro > high (TB) Myers et al. (2007) 21 low ball velocity (15.1) 65 medium ball velocity (7.8) 14 high ball velocity (1.8) Low, med. < high (TB) Low < med. < high (max) Correlation (TB, max) Lephart et al. (2007) 15 golfers (12.1) 8-week golf-specific training Pre < Post (shoulder rotation, x-factor) Cole & Grimshaw (2009) 7 low HC ( 10) 8 high HC (12-18) None

X-Factor Studies (cont.) Study Methods Results Chu et al. (2010) 266 males & 42 females (8.4) Multiple regression (TB) Joyce et al. (2010) Method study Orientation angle approach Comparison among rotation sequences Meister et al. (2011) 10 professional (scratch or better) 5 amateur (4, 15, 30, two novice) 3 effort levels (easy, medium, & hard) Within subject correlation (professional; max, impact) Issues: Heterogenous samples No direct relationship between CH velocity and X-factor Influence of the planar swing model / stretch-shorting cycle No normalization of the CH velocity to body size

Correlation: vs. Max Clubhead Velocity Maximum (BH/s) At Impact Change Clubhead 25.21 ± 1.82 24.86 ± 1.85 (r = 0.997*) -0.35 ± 0.15 Wrist 11.87 ± 2.08 (r = 0.724*) 10.32 ± 2.16 (r = 0.633*) -1.55 ± 1.05 Pr/Sup 4.17 ± 2.23 4.14 ± 2.24 -0.03 ± 0.08 Elbow 1.94 ± 1.10 0.75 ± 1.93 -1.19 ± 1.20 (r = 0.501*) SJ 4.82 ± 0.63 2.71 ± 2.24 -2.11 ± 2.14 Trunk 3.95 ± 0.67 3.25 ± 1.30 -0.70 ± 0.88 Pelvis 4.67 ± 0.84 (r = 0.539*) 3.97 ± 0.94 -0.70 ± 0.58 M Hip 0.35 ± 0.15 (r = -0.402; p = 0.10) -0.04 ± 0.15 -0.39 ± 0.23 (r = -0.475*)

Correlation: vs. Max Clubhead Velocity TB-ED (BH) TB-MD TB-BI Clubhead 0.75 ± 0.10 1.60 ± 0.13 2.41 ± 0.36 Wrist 0.02 ± 0.09 0.34 ± 0.10 0.73 ± 0.17 SJ 0.12 ± 0.06 0.31 ± 0.08 0.41 ± 0.11 Trunk 0.24 ± 0.06 0.36 ± 0.08 0.46 ± 0.08 Pelvis 0.28 ± 0.08 (r = 0.544*) 0.47 ± 0.11 (r = 0.420; p = 0.08) 0.62 ± 0.14 (r = 0.468*)

X-Factor Parameters Correlation: vs. Max Clubhead Velocity (BH/s) Maximum (deg) At BI Change X-Factor 58.2 ± 8.9 10.7 ± 8.5 -47.5 ± 8.5 Hip Line Angle 38.4 ± 7.9 -38.7 ± 9.8 (r = -0.486*) -77.1 ± 13.4 (r = -0.461; p = .05) Shoulder Line Angle 95.1 9.4 (r = 0.415; p = 0.08) -28.0 ± 8.8 (r = -0.400; p = 0.10) -123.1 ± 13.0 (r = -0.568*)

Velocity Contribution vs. Max CH Velocity r = 0.997* (*p < 0.05) r = 0.724* r = 0.633* r = 0.539* r = 0.501* r = -0.475*

Inter-Joint/Segment Correlations (p < 0.05) Pelvis Max Elbow Max Wrist Max Pr/Sup Max MH -0.471 Pelvis -0.553 0.607 Trunk -0.536 El/Depr -0.476 Elbow 0.503 -0.631 Pelvis Max SJ Max Wrist Max Pr/Sup Max MH Max 0.470 El/Depr Max 0.497 Elbow Max 0.493 -0.674

Accumulated Contribution 100% 29.9% 17.1% 19.3% 25.6%

Trajectory Contribution vs. Max CH Velocity (*p < 0.05) r = 0.468* r = 0.544*