COMENTARIOS AL CONTRATO DE REPRESENTACIÓN CON GALERÍA COMERCIAL

Posture is also regarded as a dynamic variable of balance and has been defined as the dynamics of body posture to prevent falling (Winter, 1995). Two common measures associated with postural balance are whole body centre of gravity (COG) and centre of pressure (COP). The previous literature on these topics related to the golf swing is discussed below.

The golfers COG is a weighted average of the COG of each body segment in 3D space and is controlled by the balance control system. Burden et al. (1998) is the only study to report the COG path throughout the golf swing using a driver. The COG displayed a consistent path across all right handed golfers in the backswing but there were differences in COG location at IMP. Initially, the COG moved to the golfers right and maximum displacement (range 3.4 cm - 14.4 cm) was completed before or at TB. This was combined with forward movement of the COG which continued into the downswing and was consistent regardless of hip and shoulder rotations. Approximately 0.1 seconds before IMP, the COG moved to the golfers left (target direction) and forward of the set-up position, but at IMP the COG was different for each golfer. The COG was either in front and left of its position at set-up, behind and left of

60 the set-up position or right and in front of set-up position. There was no clear reason given for this movement of COG and there was no relationship with measures of performance or a golfer’s posture (i.e. trunk forward and lateral bend). Centre of gravity investigations of fast bowling in cricket have reported that bowlers who were able to co- ordinate their bowling action with COG deceleration were more likely to generate high ball speeds (Wormgoor et al., 2010).

Centre of pressure is defined as the 2D point location (in the horizontal plane) where the resultant of all ground reaction forces (GRF) act (Winter, 1995). From baseball research, the difference between COP and COG locations (on the horizontal plane) was up to 20 cm at certain phases of the baseball swing (Welch et al., 1995). Furthermore, alignment of these measures determined rotational and linear movements of hitters which, in turn impacted on the bat velocities generated (Welch et al., 1995). Ball and Best (2007a) presented two distinct COP styles observed in the golf swing, ‘front foot’ and ‘reverse foot’. The front foot style was characterised by a balanced position at TA, moving to the back foot (which is the right foot of a right handed golfer) during the backswing then left to the front foot (which is the left foot of a right handed golfer) during the downswing and with the weight predominantly on the front foot at IMP. The reverse foot style was characterised by a shifting of weight to the left from TB through the downswing and then weight was near mid-stance during IMP before moving to the back foot during follow through (Ball & Best, 2007a). Front foot style golfers with greater range of COPM-L movement and increased rate of COP movement to the front foot in the downswing were associated with higher club head velocity. The reverse foot golfers with higher club head velocity had COP measures near mid-stance and greater rate of COP towards the back foot at IMP. The authors stated it was important to identify strategies within each style before links to performance could be deduced. Therefore, it appears that the range and rate of change of COP were points of interest in both COP styles. However, in the 308 golfers examined by Chu et al (2010) only the front foot style, defined using the ratio of vertical GRF between the front and back feet, was observed. Alternatively, the decreasing magnitude of vertical force in the front foot towards impact coupled with an upward translation of the pelvis were stronger predictors of clubhead linear velocity. Therefore, there appears to be disagreement between studies on COP patterns during the golf swing. Nevertheless, Ball and Best (2007b) commented that neither style should be viewed as a technical error as there

61 were no differences in clubhead velocity at impact observed between styles. Instead, it was deemed more important to identify the different strategies used to perform the golf swing in order to make appropriate coaching recommendations. Both these studies only examined part of the notion of postural balance, as variables such as COG and postural kinematics were not examined simultaneously. In addition, perturbations to a normal erect posture (i.e. leaning forward or backwards) during gait has been shown to affect postural responses (i.e. moments) in the hip, knee and ankle based on the inverted pendulum model of balance (Winter, 1995). Therefore, this emphasises the need to collect both kinematic and kinetic data (e.g. GRF data) when examining posture during the golf swing. An area that has not been readily investigated is the ability of golfers to repeat patterns in weight transfer.

The coaches in the perception study also identified the importance of postural balance and discussed the idea in terms of positioning a golfer’s COG correctly and their weight transfer (§‎2.5.4, p32) which echoes Winter’s (1995) definition of balance. Often the coaches would make reference to a golfer’s postural kinematics as a means of creating a balanced position throughout the swing (§‎2.5.4, p32). For example, one coach described the need to “match” certain parameters during the golf swing which may be achieved by collecting both kinematic, kinetic and measures of performance.

3.5.4 Future Research Recommendations

Golf posture has only been partially investigated in the biomechanical literature. The variables defining golf posture need to be more completely identified and their effect on measures of performance, such as shot accuracy or repeatability of measures of performance quantified. This may require the development of new methodologies to describe 3D trunk kinematics through multiple segment models. The relationship between postural kinematics and postural balance also needs to be established. Finally, the relationship between posture and other key technical parameters, such as body rotation require investigation.