Putting stroke kinematics

Brooks (2002) described three types of putting strokes commonly recommended by golf instructors, in reference to the target line and are; the straight back to straight through; inside to inside; and inside to straight through. After examining the strokes using mathematical models Brooks (2002) did not arrive at a conclusion to which stroke is best, however, a putting stroke where during the backswing the putter head moves inside the aim line, and where the putter face is square to the putter path, which means the putter face is open to the aim line at the end of the backswing was endorsed. Pelz (2000) advocates a different type of putting stroke, where the path is linear and the putter face is square to the path throughout the stroke. Pelz (2000) recommends this type of stroke with the putter face square, as there may be timing limitations, resulting in the inability to square the club face exactly at impact. The main argument against what was proposed by Pelz (2000) is that the straight stroke is more biomechanically complex

than it first seems, as it relies on a fully horizontal axis of rotation for the putter, and/or muscle activity that will compensate for the deviation from the horizontal axis (Karlsen et al. 2008).

Neal and Wilson (1985) modeled the golf putt as a double-pendulum system composed of two arms and the putter. It was described that the shoulder is meant to roll in an up-and-down fashion, and the two hands hold the putter, moving back and forth in a symmetrical pattern (Neal & Wilson, 1985). Delay, Nougier, Orliaguet and Coello, (1997) however observed novices to show the typical pendulum motion, whilst expert players did not. Expert players demonstrated an asymmetrical pattern where a longer follow-through was observed (Delay et al. 1997; Sim & Kim, 2010).

Sim and Kim (2010) analysed the differences between experts and novices accuracy in golf putting in regards to impulse variability. An impulse variability model was developed by Schmidt, Zelaznik, Hawkins, Frank and Quinn (1979), to send a ball close to the target, the magnitude of the impulse applied to the ball by the putter needs to be precise. In putting, the moment of impact is extremely brief, therefore the velocity of the putter at impact becomes extremely important in achieving accuracy (Sim & Kim, 2010). Research has demonstrated that movement at impact is not decided upon the moment of impact, but that movement is attuned and planned from initiation of the movement (Bootsma & van Wieringen, 1988; Coello, Delay, Nougier & Orliaguet, 2000) and through the period of swinging up to impact referred to as downswing (Müller & Abernethy, 2006). Delay et al. (1997) suggests that movement control may not be complete at impact.

Sim and Kim (2010) results showed expert players to have a lower level of velocity in comparison to the novice group, the experts also achieved increased accuracy; Delay et al. (1997) reported the same results. The question raised from both of these sets of results is how the expert group reached the target with a lower velocity. Delay et al. (1997) suggested that energy produced by novices might not entirely be transferred to the ball, with more energy loss at the moment of impact. Sim and Kim (2010) support this claim as it was observed that expert players maximum velocity occurred after impact, which means the ball gained stronger impulse when it left the putter face rather than at the moment of impact. A second explanation was provided by Delay et al. (1997), which concerned the ball roll. During experimentation it was observed that the novice players ball often bounced during rolling, whereas the experts ball glided smoothly. Sim & Kim (2010) further this theory of different types of ball roll; they suggest expert players achieve greater energy efficiency by striking the ball with the putter during the rising phase of the stroke while increasing velocity so that it rolls rather than slides towards the target. This would explain how the

expert players reached the target with reduced impact velocity as a ball will lose less kinetic energy when it rolls in comparison to when it slides (Sim & Kim, 2010).

MacKenzie and Sprigings, (2005) state that a number of elements are needed to hit a successful putt. The first being that the golfer must correctly read the green, to determine the correct target line and establish the optimal speed to impact on the golf ball to project it towards the target (hole). During the execution of the putting stroke the putter should only demonstrate horizontal velocity in the direction of the decided target line, reducing elements of velocity in other directions, which would be undesirable. This will ensure the plane of the putter face with be perpendicular to the original putting line (MacKenzie & Sprignings, 2005). A technique that can be used to read the green is the plumb-bob method; this is where the golfer stands behind the ball straddling an imaginary line that bisects the hole (MacKenzie & Sprignings, 2005). The golfer then suspends the putter at an arm’s length in front of the face allowing gravity to pull the shaft into a true vertical alignment (Foston, 1992). Although it has been proven a success in certain professionals Mackenzie and Sprigings (2005) deem it to be an unreliable method at determining the intended target line due to the high sensitivity of the plumb-bob method to confounding factors.

Karlsen et al. (2008) examined the golf putting stroke and determined three main determinants of direction variability. These were putter face angle that was accountable for 80% of the variability, putter path accounted for 17% variability and the horizontal impact point on the putter face accounted for 3% (Karlsen et al., 2008). Pelz (2000) only considered two factors that contribute to direction variability, firstly, putter face angle (83%) and putter path (17%). Therefore it may be the case that putter face angle may be the most important club head kinematic variable regarding golf ball direction variability as highlighted by Karlsen et al. (2008) and Pelz (2000). To date no study has examined body movements effect on putter face and performance variability.