Golf Coaches’ Perceptions Of Key Technical Swing Parameters (P7)
In the golf biomechanical literature, body rotation, typically quantified by axial rotation of the central body segments, has been widely investigated and linked to performance outcomes, such as clubhead velocity. Many studies have reported pelvis and trunk axial rotational angles at various stages of the swing including at TA, TB, IMP, middownswing, last 40ms prior to impact as well as the peak magnitudes. Hume reported trunk axial rotation of 78 – 102º and pelvis axial rotation of 47-55º at TB depending on golfer ability and the club being used and also suggested that trunk flexion, lateral bend and knee angles should be observed as they could influence axial rotation.
Several authors have suggested that the separation between pelvis and trunk axial rotation (i.e. X-factor) was more important for power generation. Chu reported that X-factor at TB explained approximately 25% of ball velocity with a driver and the authors suggested that golfers should focus on increasing separation between trunk and pelvis rotation in order to increase ball velocity. Maximum X-factor during the downswing was shown to strongly correlate with clubhead linear velocity at IMP (~ 74%) and a moderate correlation was found between ball velocity using a driver and X-factor at TB (~ 30%). The authors concluded that X-factor at TB and downswing maximum contributed to the rotation velocities of the upper torso which, in turn contributed to increased club and ball velocity.
The difference in X-factor between TB and downswing maximum value (termed X-factor stretch), has been suggested as more important than the maximum X-factor alone. The greater X-factor stretch (mean 13.4º) in highly skilled golfers (handicap < 0) compared to a lower skilled golfer (handicap > 15) (mean 0.5º) was considered to contribute to the greater shot distance for the higher skilled golfers. It is important to note that the differences in how TB is defined could affect the value of X-factor at this part in the swing and subsequent X-factor stretch calculations. The rate of stretch and recoil describes the speed with which the trunk and pelvis separate and align providing a measure of rotational power. Golfers with greater driving distance are suggested to display greater maximum rates of recoil in the downswing. Nevertheless, there are limited studies that have investigated this idea further. The proposed mechanism for increased separation between trunk and pelvis and the timings of rotations was due to a stretch-shorten cycle within the spinal rotator muscles, leading to increased trunk acceleration and in turn increased club acceleration. In contrast, studies on female golfers have not provided support for the stretch-shortening mechanism of trunk muscles during the downswing for increasing clubhead linear velocity.
The repeatability of rotational parameters have also been investigated. Peak trunk axial rotation has been shown to have lower variability as shot intensity increased, while peak pelvis rotation repeatability was greater than trunk rotation repeatability across all shot intensities. The rotational par ameters at IMP displayed larger coefficient of variation (COV) than the peak values, which may be a consequence of consistently identifying the IMP position or how COV is defined. Horan et al. examined movement variability of rotational parameters using standard deviations (SD) at key stages of the swing (TB, mid-downswing, IMP) and using spanning sets across continuous phases of the swing in male and female golfers. Female golfers were reported to have greater axial rotation variability for the pelvis at mid-downswing and IMP and trunk at IMP than males. However, the authors could not explain these differences in variability.