The Importance Of Wrist Torque In Driving The Golfball (P5)

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Results

The second simulation condition (SIM-2) successfully showed that it is possible to reach the desired impact position with the clubshaft vertical without using muscular wrist torque during the downward swing (Figure 4C). The maximum horizontal clubhead speed reached in SIM-2 was 40.4 m/s (~91 mph; Figure 2), which is approximately 3.6 m/s (8 mph) slower than that achieved using SIM-1, where wrist torque was permitted. As in SIM-1, the onset of the voluntary muscular torque for the torso and the arm segments in SIM-2 was proximal to distal in nature, with the arm’s shoulder torque generator being activated 0.080 s after the onset of the torso’s torque (Figure 5). With the absence of voluntary wrist torque, the time of the downward swing (0.344 s) was slightly shorter by 0.036 s than it was when wrist torque was employed. This difference was somewhat surprising considering that the final velocity reached by the clubhead was significantly greater when wrist torque was applied. The explanation for this finding can be traced to the increased angular displacement of the torso segment observed in SIM-1. By increasing the angular displacement of the trunk, the arm’s rotation relative to the trunk was delayed which, in turn, delayed the uncocking of the wrist (Figure 6). The net result was a higher speed of the clubhead at impact for SIM-1 compared to SIM-2, but developed over a longer time period as a result of the greater use of torso rotation.

Profiles of the joint torque histories when the wrist torque generator was disabled
Figure 5 – Profiles of the joint torque histories when the wrist torque generator was disabled (SIM-2). The clubhead reaches a speed of 40.4 m/s (91 mph).
Angular displacements of the joints of the three segments under two conditions: (a) wrist torque generator enabled
Figure 6-Angular displacements of the joints of the three segments under two conditions: (a) wrist torque generator enabled; and (b) wrist torque generator disabled.

The results of the third simulation condition (SIM-3), in which the force-velocity property of muscle was removed from the torque generators, revealed that a significantly higher clubhead speed (<57 m/s, or 128 mph) could be reached at impact, in a shorter period of time (0.248 s), even while constrained by the same upper torque limits that were imposed on SIM1. However, the asymptotic shape of the associated muscular torque profiles (Figure 7) are unrealistic when compared to the shape of the muscular torque profiles for real golfers that were determined by means of inverse dynamics (Neal et al., 1999). Removing the forcevelocity constraint from the simulation model had the effect of activating the wrist torque later in the simulation. Specifically, for SIM-3, the simulated muscular wrist torque was activated when the arm was approximately 60° below a horizontal line projected through the shoulder joint, as compared to 30° when the force-velocity property was incorporated into the model.

Profiles of the torques produced by the joint generators when the force-velocity property of muscle was not incorporated into the model
Figure 7 – Profiles of the torques produced by the joint generators when the force-velocity property of muscle was not incorporated into the model. The clubhead reaches a speed of 57 m/ s (128 mph).

Discussion

Every model is an approximation to the truth, with many variables being neglected that are judged or calculated to be of minor importance to the conclusions reached (Hubbard & Trinkle, 1984). The necessary level of complexity that one builds into a simulation model depends on the question under study. Alexander (1990, 1992) and Hubbard (1993) caution against the use of complex mathematical models whose results become impossible to interpret because of the large number of inextricably intertwined independent variables. From the general agreement of the results with those of a recognized elite professional golfer, it appears that a simple 2-D, three-segment model, using a single activation control strategy with specialized torque generators at the proximal ends, has sufficient modeling detail to predict the optimal timing necessary to achieve maximum clubhead speed at impact.

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