1. 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

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

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

4. 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

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

6. 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

7. 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

8. 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%)

9. 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

10. 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

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

12. 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

13. 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

14. 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%

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

16. X-Factor Parameters

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

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

19. 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

20. 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.

21. 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

22. 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.

23. Thank you for
your attention!

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

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

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

27. 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

28. Normal Velocity ContributionUp
Down

29. Radial Velocity Contribution
Toward

30. 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

31. Motion Planes

32. 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

33. 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

34. 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 = ; p = 0.10)
-0.04 ± 0.15
-0.39 ± 0.23
(r = *)

35. 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*)

36. 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 = *)
-77.1 ± 13.4
(r = ; p = .05)
Shoulder Line Angle
(r = 0.415; p = 0.08)
-28.0 ± 8.8
(r = ; p = 0.10)
± 13.0
(r = *)

37. 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 = *

38. 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

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

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