Golf players exhibit changes to grip speed parameters during club release in response to changes in club stiffness

Reliability of repeat golf club testing sessions with modified club moment of inertia

The moment of inertia of a golf club, quantified about an axis at the butt of the handle, normal to the swing plane, has the potential to influence both clubhead and ball velocity. The purpose of this study was to assess the reliability of clubhead and ball velocity with changes to moment of inertia over repeat testing sessions and, if reliable, to quantify the effect of modifying moment of inertia. Eleven skilled male golfers hit 20 golf shots with three golf clubs, each with a different moment of inertia achieved through adding mass inside the club shaft and repeated this protocol over three sessions. A commercially available launch monitor was used to measure both velocity variables. Test–retest reliability was assessed via (1) limits of agreement, to determine reliability from a change in magnitude perspective and (2) linear-weighted kappa, to determine reliability from a directional perspective. The effect of moment of inertia on clubhead and ball velocity was determined using one-way, repeated measures analysis of variance tests, with partial eta squared being used to quantify the size of the effect. Increasing golf club moment of inertia reliably decreased clubhead and ball velocity, with fair to substantial kappa results revealed between sessions. The magnitude of decrease in these velocities, however, could not be reliably quantified. Statistically, the influence of moment of inertia was considered large (η2 ≥ 0.662 and 0.404) and significant (p < 0.001 and ≤ 0.006) for both clubhead and ball velocity, respectively.

A preliminary investigation of trunk and wrist kinematics when using drivers with different shaft properties

It is unknown whether skilled golfers will modify their kinematics when using drivers of different shaft properties. This study aimed to firstly determine if golf swing kinematics and swing parameters and related launch conditions differed when using modified drivers, then secondly, determine which kinematics were associated with clubhead speed. Twenty high level amateur male golfers (M ± SD: handicap = 1.9 ± 1.9 score) had their three-dimensional (3D) trunk and wrist kinematics collected for two driver trials. Swing parameters and related launch conditions were collected using a launch monitor. A one-way repeated measures ANOVA revealed significant (p ≤ 0.003) between driver differences; specifically, faster trunk axial rotation velocity and an early wrist release for the low kick point driver. Launch angle was shown to be 2° lower for the high kick point driver. Regression models for both drivers explained a significant amount of variance (60-67%) in clubhead speed. Wrist kinematics were most associated with clubhead speed, indicating the importance of the wrists in producing clubhead speed regardless of driver shaft properties.

The influence of golf shaft stiffness on grip and clubhead kinematics

The purpose of this study was to investigate the influence of shaft stiffness on grip and clubhead kinematics. Two driver shafts with disparate levels of stiffness, but very similar inertial properties, were tested by 33 golfers representing a range of abilities. Shaft deflection data as well as grip and clubhead kinematics were collected from 14 swings, with each shaft, for each golfer using an optical motion capture system. The more flexible shaft (R-Flex) demonstrated a higher contribution to clubhead speed from shaft deflection dynamics (P < .001), but was also associated with significantly less grip angular velocity at impact (P = .001), resulting in no significant difference in clubhead speed (P = .14). However, at the individual level, half of the participants demonstrated a significant difference in clubhead speed between shafts. The more flexible shaft was also associated with significantly different magnitudes of head rotation relative to the grip. More specifically, both bend loft (P < .001) and bend lie (P < .001) were greater for the R-Flex shaft, while bend close (P = .017) was greater for the stiffer (X-Flex) shaft. However, changes in grip orientation resulted in no significant differences in face orientation, between the shafts, at impact.