Kmatics Golf Swing References Book 1

Nesbit, using a full-body modeling approach, determined that the hub path deviated considerably from constant radius motion. The study found that the ratio of the radius of the path at the top of the backswing to the radius at impact correlated strongly with skill level. Miura, studied the effects of the inward pull action of the golf club at impact and determined that this action increased the energy transfer to the club and the resulting club head velocity. Miura also determined that this action was a characteristic of a skilled golfer. It is hypothesized the hub path is geometrically complex yet purposefully and uniquely configured, and that the non- circular aspect of the hub path is integral to the control of the club trajectory, the generation of maximum club head velocity, and the transference of the kinetic quantities generated by the body to the club.

Thus the objectives of this study are to analyze and describe the geometric and kinematic characteristics of the hub path of the golf swing, and to determine the particular functions of the hub path geometry in transferring the force, torque, work, and power generated by the golfer to the club. The approach taken in this study is to comprehensively analyze, interpret, and present the results for a small group of diverse subjects. Analyzing a large pool of subjects and performing a subsequent statistical analysis of the phenomena is beyond the scope of this study.

Figure 1 illustrates the free-body-diagram of the model used to perform this study.

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The model with representative mass and inertia properties, constrains the swing to one non-moving plane Colman and Anderson, , ignores rotations about the club shaft, and treats the shaft as rigid. The X-Y coordinate system is in the plane of the swing and fixed to the ground global coordinate system. The N-T coordinate system local coordinate system is attached to, and moves with grip point A along the hub path, and orients normal to the path pointing towards the center of curvature N-component , and tangent to the path in the direction of motion T-component.

The following equations of motion were developed from Figure The acceleration of the club mass center is given by the following relative acceleration vector expression:. Data to kinematically drive the model are obtained from subject golf swings. The system tracks passive-reflective markers that are placed on the golfer and the club.

Only the data from the markers on the club are necessary to drive this model. The three markers on the club are arranged in a rigid triad that is attached to the shaft just below the handgrip. Two of the markers are aligned with the long axis of the club shaft, and the third is offset perpendicular to the club shaft and parallel to the club face see Figure 1. The three-dimensional marker triad paths are recorded at Hz then smoothed and processed to yield global body angular motions of the club and the three-dimensional global positions of the hub path using methods described in Nesbit, The orientation of the swing plane X-Y plane during the downswing is established from the angular motion data Coleman and Rankin, The global position data of the hub path and global orientation of the club are mapped onto this plane using methods described in Kane et al.

With the accelerations of the club specified, Equations 1 through 3 are solved to determine the time histories of the applied linear force F X and F Y and the swing torque T. Note that the linear force and hub accelerations are also resolved into normal and tangential components since these components align well with the changing direction of the hub path normal component and changing speed along the hub path tangential component. From the linear force components and swing torque at the club handle, the total work done by the golfer on the club is determined from the following:.

The total power is determined by numerically differentiating the work expression of Equation 7. The total work and power quantities are comprised of the contributions from the linear force linear work and power and swing torque angular work and power. Four amateur golfers, three males and the one female had their golf swings analyzed for this study. All subjects are right-handed and their relevant data are given in Table 1. A diversity of skill levels and swing styles was the criteria for selecting these subjects in an attempt to yield a range of results Nesbit and Serrano, ; Nesbit, Stylistically, the male scratch and male 5H subjects had aggressive, powerful, and quick swings, whereas the male 13H and female 18H subjects had smoother, longer, and slower swings.

Informed consent for the following procedure was obtained from all subjects. Each subject had reflective markers placed upon their body. A rigid triad of markers was attached to the club near the top of the shaft.

Kmatics Golf Swing References Book 1 eBook: Christopher Myers: www.newyorkethnicfood.com: Kindle Store

The Motion Analysis system was calibrated until the combined 3D residual for all cameras was under 1. The subjects were asked to execute a series of swings that included hitting a ball into a net. The subjects were advised to swing the club in a manner similar to hitting a driver in a competitive situation where distance and accuracy were both important. Subsequently, several swings from each subject were recorded and tracked then presented to the subjects for their review. The subjects each selected what they considered to be their most representative swing in terms of club head velocity, impact feel, partial flight of the ball, and overall visual assessment of the motion capture data.

This single self-selected swing from each subject was then analyzed for this study. This manner of conducting trials and selecting swings for subsequent analyses is consistent with previous studies Nesbit and Serrano, ; Nesbit, Superimposed illustrations of the subject swings are shown in Figure 2.

The swing is shown starting from thetop of the backswing through a significant portion of the follow through. Each frame represents 0. The kinematic and kinetic quantities predicted by the model that are of interest for this study are given in Table 2 for all subjects. The data represent the maximum values that occurred during the downswing.

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The table also gives the relevant references for previously reported data where applicable. The hub path during the downswing for all subjects is shown in Figure 3.

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The radius of the hub path as a function of time before ball contact is shown in Figure 4. Referring to Figure 4 , phase I starts with the initiation of the downswing which generally corresponds to the first local radius maximum, and ends with the first local radius minimum roughly halfway through the downswing. Phase II goes from the first local radius minimum to the second local radius maximum near ball contact. Phase III goes from the second local radius maximum to ball contact.

These three phases of the downswing are shown for the scratch golfer in Figures 5a, b, c. The figures also show the path and direction of movement of the center-of-curvature. The data are normalized to a percentage of the maximum value experienced during the downswing see Table 2. The percent change refers to the difference in the value from the beginning to the end of the phase. Note that not all quantities were initially zero at the beginning of phase I. The following discussions are limited to the downswing portion of the golf swing.

Much of the kinematic and kinetic data output by the computer model Table 2 have been previously reported. There appears to be sufficient agreement with published data to yield confidence in the model output. The range of the kinematic and kinetic quantities among the subjects is considerable and quantitatively emphasize the differences in their swing mechanics, a finding supported by Nesbit, Of note is the individual nature of the inner hub path, its non-constant radius, and shifting center of rotation for all subjects.

Thus the goal of analyzing a diverse set of swing styles from a mechanics point of view was achieved. Figure 3 demonstrates that there are considerable differences in the size, shape, changing radii, and shifting center-of-curvature of the hub path among the subjects. Figure 4 illustrates that that the radius of the hub path changes significantly during the downswing, and that the minimum, maximum, and range of radii values for the subjects vary considerably. However there appears to be a pattern associated with the changing hub radius.

For all subjects, the local maximum radii occur near the top of the backswing 0. All subjects exhibit a sharp reduction in radius near ball contact as identified by Miura, which has been related to skill level Nesbit, For the male scratch subject, from the initiation of the downswing until the hands are halfway around the swing hub 9: The club remains fairly close to tangent to the path during this phase as the golfer is primarily pulling the club along the hub path. Here, the radius of the hub path starts at a local maximum and decreases during the entire phase to its first local minimum.

Phase II Figure 5b begins with the hands at the 9: This phase sees considerable outward movement or un-cocking of the club relative to the path. During Phase III, which takes the club to ball contact Figure 5c , the center of curvature moves sharply downward as the path radius decreases to its minimum value at ball contact Here, the club continues to move outward relative to the path and becomes perpendicular to the path at ball contact.

A three-phase delineation of the downswing is presented by Miura, which loosely corresponds time-wise with this demarcation, however it is based upon relative wrist movement, arm rotation, and energy transfer, not hub path characteristics. In the discussions that follow, the reader should refer to Figures 5a, b, c to relate the phases to the relevant portion of the downswing, and note that the quantities in parentheses are for the subjects as follows: The maximum hub path linear grip velocities were found to be very similar among the subjects A slight but distinct increase in the slope of the velocity profile was evident at the transition between phase I and phase II for all subjects.

The increasing path radius during phase II appears to enhance the rate of increase in hub velocity. Three of the four subjects reached their peak grip velocity values at the end of the phase II. The grip velocity remained nearly constant during phase III for the male scratch subject, reduced slightly for the male 5H and male 13H subjects, and increased slightly for the female 18H subject. Relationships between the linear acceleration components of Equations 5 and 6 , and hub radius phases can be better identified when the accelerations are resolved into tangential and normal components.

The differences in the maximum tangential acceleration values were a result of the relative smoothness of their swings which had little effect on the maximum hub path velocities. The tangential component of the hub path accelerations had similar phase related characteristics as hub path velocity. The tangential acceleration was initially 6.

Here again, the increasing path radius during phase II appears to enhance the rate of increase in tangential acceleration. The tangential acceleration dropped during phase III and reached 0, These values imply that a relative delay then more rapid increase of the tangential acceleration is desirable. The differences in the profiles and maximum values of the normal acceleration for the subjects resulted primarily from differences in the hub path radius profiles since the velocity profiles were similar.

The increase during phase III was a result of the significant reductions in hub radii for all subjects since their linear velocities were relatively constant during this phase. The normal acceleration was nearly maximum at ball contact for all subjects even in cases when hub path linear velocity was not maximum.

This occurrence was a result of all subjects reaching a local minimum radii at ball contact. The rate of increase of normal accelerations was fairly uniform over the three phases for three of the subjects. This uniformity requires a complex interaction between hub path velocity and radius during the downswing. The maximum swing torque values differed considerably among the subjects All subjects initiated the downswing with a relatively high percentage of their maximum swing torque Even though the swing torques were relatively high during phase I, there was little outward movement of the club relative to the hub path.

The low club handle velocity coupled with the initial large hub path radius minimized the centrifugal loading on the club thus reducing the tendency of the club moving outward. For all subjects, the initiation of phase II coincided with their first local hub radius minimum, while applying the majority of their respective maximum swing torque, and reaching about half of their respective maximum grip velocity. During phase II, as the club moved outward, the wrist torques continued to increase accelerating the angular motion of the club. The increase in hub path radius during this phase may be a result of the golfer shifting the effort from controlling the hub path to applying maximum wrist torque, or it could simply be a third-law reaction to the rapid outward movement of the club.

During phase III, all subjects experienced a significant reduction in swing torque - , During phase III when the hub radius reduced rapidly, the wrist torques decreased toward zero at ball contact. During this phase, the wrist torques continued to contribute somewhat to the acceleration of the club.

Relationships between the linear force and hub radius phases can be better identified when the force is resolved into its tangential and normal components see Figure 6. The maximum value of the linear force , , , N, the tangential component maximum , , , N, and the normal component maximum , , , N showed considerable differences among the subjects. For all subjects, the maximum normal force component exceeds the maximum tangential force component by nearly a two-to-one ratio.

Thus the golfer exerts considerably more effort in controlling the path of the club than linearly accelerating the club. The direction of the linear force is initially tangent to the path and at ball contact is normal to the path. Thus the direction of the force moves progressively inward relative to the hub path as the downswing progresses. At the end of phase I, the direction of the force is still mostly tangent to the path.

By the end of phase II, the direction is about 45 degrees inside the hub path, and by the end of phase III, it is normal to the hub path. The tangential component is initially During phase III the tangential force drops rapidly - , The function of the linear force appears to change as the downswing progresses.

During phase I, the majority of the force is tangent to the path and primarily functions to accelerate the club. The subjects apply the majority of their respective maximum tangent force by the end of phase I while applying little of their respective maximum normal force in controlling the hub path. Only modest effort is required to reduce the path radius during this phase because of the low club velocity. The tangential force continues to increase during phase II and reaches maximum at the end of the phase which coincides with the subjects reaching their local maximum radii.

During this phase the normal force increases more slowly and reaches between a quarter and half of maximum by the end of the phase. Even though the club head velocity is quite high at this point Write a product review. Get to Know Us. Not Enabled Word Wise: Enabled Average Customer Review: Be the first to review this item Would you like to tell us about a lower price?

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