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A possible limitation of previous studies examining weight transfer is the lack of examination of swing styles or movement strategies in the golf swing prior to performance analysis. A style or movement strategy is the performance of a skill in different ways to achieve the same aim. Two examples of obviously different styles in sport are single versus double handed backhand in tennis and the slide approach compared with the rotational approach in shotput. In golf, Meadows (2001) reported

three different strategies for gripping the golf club: the interlocking grip, the overlapping grip and the baseball grip.

Less obvious is the existence of styles in the golf swing itself. However, different swing styles of professional golfers are often discussed in the media and have been noted in the coaching literature. For example, Suttie (2006) reported that, based on his “long years of teaching” all golfers fitted best into one of four categories based on the golfer’s physical traits and how the golfer develops power: the upper body, the lower body, the hands and a swing style termed “Classic” by Suttie which displayed an “unusually high degree of rhythm, timing and balance”. Upper body players possess shorter than normal arms and developed power from the shoulder muscles. Lower body players are taller, athletic players with long legs from which power is developed. Hands players possess large hands and forearms from which power is developed. Classic players are smooth, effortless and balanced, as well as being athletic with long arms.

Different styles in the golf swing have been reported, albeit with no objective data, in the scientific literature. Nagano and Sawada (1977) reported two styles of swing arc based on observation of the trace of the club head viewed in the vertical plane parallel to the line of shot. Swing golfers exhibited an elliptical orbit from takeaway to the end of follow through while ‘hitters’ exhibited a horizontal or oblique type swing. This was the limit of the definition of the swing styles. Neal (1998) used a golf coach to identify two styles of swing: a left-to-right and a rotational style of swing, although no definition of the two styles was presented. However, objectively assessed differences in swing styles or strategies do not exist.

Only two golf studies examining weight transfer have considered styles, or movement strategies, in their research design. In Neal (1998), a golf coach subjectively defined two styles in low handicap golfers; a ‘rotational’ style and a ‘left to right’ style. Koslow (1994) used a Sporttech swing force plate data to identify different weight transfer styles in novice golfers and reported three statistically different styles:

1. Normal (balanced at address, towards the back foot in backswing and towards the front foot at ball contact. Koslow reported this sequence as the “coach defined method of weight transfer”).

2. Reverse pivot (balanced at address, on front foot at the top of backswing and on the back foot at ball contact).

3. Incomplete (balanced at address, back foot at backswing and back foot at ball contact).

Koslow (1994) reported that 84% of novice golfers did not exhibit the Normal pattern, producing instead a Reverse pivot or an Incomplete weight transfer. It is important to note that although different weight transfer patterns existed in the

Koslow study, two of the three styles were considered errors by the researchers rather than useful techniques. This is an important distinction because different movement strategies within a skill can be valid methods of performance, or can represent errors in movement that reduce performance. That is, a particular style can be effective or it can be ineffective.

Neal (1998) compared two coach-defined and coach-identified styles among 14 low handicap golfers. These groups were defined as ‘left-to-right’ and ‘rotational’ but the

criterion for each style was not reported. As low handicap golfers (i.e. highly skilled) were used, both of these styles might be considered to be valid techniques and not technical errors, although this was not stated by Neal. Differences were found between these groups in the ratio between the CP range perpendicular to the line of hit (CPx) and CP range parallel to the line of hit (CPy) between the groups (Left to right: 0.29, Rotational: 0.39, p < 0.05). Neal reported that the ‘left-to-right’ style produced greater CPy movement, or movement between the left and right foot (hence the ‘left-to-right’ term for this style) and less CPx movement compared to the

rotational style (p < 0.05). As well, the ‘left-to-right’ group reached maximum forward position of CPy later in the swing (expressed as a percentage of the time between top of backswing and ball contact - Left to right: 99%, Rotational: 87%, p < 0.05). Neal (1998) did not report a description of the styles and, statistical analysis results were limited to alpha levels of p < 0.05 only, limiting further discussion.

If different styles existed in the samples tested in previous weight transfer research, statistical errors would have been made. Styles such as the two described by Neal (1998) occurring within the same dataset could generate type 1 or 2 errors in statistical analyses. Type 1 errors might exist in data due to the existence of two distinct groups (i.e. two distinct styles). Two groups (styles) can produce a large effect in regression statistics (e.g. figure 2.9 a) due only to the relatively large difference between the groups, with no relationship evident within the groups

themselves. It could also produce type 2 errors in the case of comparison of handicap groups by increasing intra-group variance and reducing statistical power. Bates (1996) stated that if different movement strategies exit, then statistical power will be lowered and there is a greater likelihood of falsely supporting the null hypothesis in

group comparison statistical procedures. Type 2 errors might also exist in regression statistics where no significant correlation exists for the whole group while significant correlations do exist within each group (e.g. figure 2.9 b). The lack of attention to possible style differences (or different movement strategies) may be a reason why many studies failed to find significant associations between weight transfer and performance, or why significant results were found in some studies.

a – correlation on a group basis due to the existence of two groups in the data

b – no correlation on a group basis but correlations within two groups within the data

Figure 2.9: Examples of statistical errors that can exist where different styles or movement strategies exist within the dataset.