Measurement of grip force and evaluation of its role in a golf shot

This study was conducted with the aim of establishing a method to measure time-varying forces at multiple locations at the hand-grip interface, using this method to record how golfers of varying abilities grip the club during a standard tee shot and investigating a potential link between the variations in vibration seen at the grip and the grip force applied near impact. It is hoped that additional knowledge about grip force during a golf shot will lead to improved training techniques and grip design in the future. An assortment of technologies were available for the measurement of grip force, but thinflexible sensors were chosen as they could be applied to the grip or gloves without altering the characteristics of the club. Reliability and performance for these sensors were not well established and, therefore, a novel set of tests were developed to evaluate their capabilities. Thin-film force sensor performance was examined under controlled laboratory conditions to give an indication of each sensor's quasi-static accuracy, hysteresis, repeatability and drift errors, dynamic accuracy and drift errors, and the effects of shear loads and surface curvature. With this newly developed set of tests, five varieties of thin-film force sensor utilizing four different technologies were assessed. The sensors had varying levels of success under the controlled conditions of the evaluation tests. Three of the sensors performed well under static and quasi-static loading conditions, with accuracy errors of 10% or less, hysteresis errors near 6%, repeatability near 6% or below, and drift at 60 s after load application under 15%. Two of these sensors were further tested and demonstrated little change in sensor output to loads applied over curved surfaces, although shear sensitivity and dynamic accuracy errors were more substantial. It was also found that some of the sensors lost sensitivity with repeated loading. Even with these drawbacks, the potential of these sensors to provide useful grip force information was clear. With an understanding of sensor performance in controlled laboratory settings, one sensor type was used to determine regions of peak pressure at the hand-grip interface and three others were used in player tests to obtain time-varying measurements of grip force during a swing. During the player tests, grip force was measured for 10-12 tee shots and impact time was determined Total force was computed for each shot taken by summing the force output of all the sensing elements positioned on either the grip or gloves. When these total force traces were aligned by impact and plotted for each of the golfers tested, an interesting and previously unreported phenomenon became apparent. Each player appeared to have their own grip force 'signature', i.e. total grip force for a particular golfer was very repeatable, but varied considerably between golfers. A grip force signature existed for all players tested regardless of ability, and the level of consistency for an individual golfer and the similarities between golfers was analysed using a cross correlation. It was found that nearly all of the golfers tested had swings that were dominated by the left hand, and that the most notable contributions of the right hand occurred after impact. Variations in grip force were also related to key phases of the swing using high speed video footage. Previously it has been noted that for the same ball, club, and impact location that the vibration on the shaft is remarkably consistent for many different golfers but there is a much greater variation in the vibration at the grip. It was hypothesized that the way a golfer grips the club affects the way vibration is transmitted into their hands and arms. A final set of player tests was therefore conducted with the aim of identifying how grip force affects vibration transmission from the shaft to the hands and the players' perceptions of this vibration. Vibration was measured on the shaft just below the grip and on the golfer'S left thumbnail, force was monitored at 18 locations on the hands, and impact location and clubhead speed were recorded. Each golfer's perceptions of the vibration caused by impact were also noted for two standard drivers. It was found that changes in the amount of vibration travelling from the shaft into the hands is affected by the grip force applied by the golfer. This is the first study to analyse the effects of grip force on vibration transmission into the hands and arms due to a golf impact.