Different centre of pressure patterns within the golf stroke I: Cluster analysis.

Weight transfer research in the golf swing has produced conflicting and inconclusive results. A limitation of previous studies is the assumption that only one swing "style" exists within the golf swing. If different styles, or movement strategies, exist and if the different styles are analysed together in a single group, statistical errors will result. The aim of this study was to determine if different weight transfer styles exist in the golf swing by applying cluster analysis to centre of pressure (CP) patterns in the direction of hit (CPy) and to evaluate cluster analysis issues. Sixty-two professional to high handicap golfers performed simulated drives, hitting a golf ball into a net, while standing on two force plates. Centre of pressure position relative to the feet (CPy%) was quantified at eight swing events identified from 200-Hz video. Cluster analysis identified two major CPy% styles: a "Front Foot" style and a "Reverse" style. Both styles began with CPy% positioned evenly between the feet, moved to the back foot during backswing, and then forward during early downswing. Beyond early downswing, the Front Foot group continued to move CPy% to the Front Foot through to ball contact, while the Reverse group moved CPy% towards the back foot through ball contact and follow-through. Both weight transfer styles were evident across skill levels from professional to high handicap golfers, indicating that neither style was a technical error. Cluster analysis should include hierarchical and non-hierarchical clustering and use objective measures combined with theoretical assessment to determine the optimal number of clusters. Furthermore, a number of validation procedures should always be used to validate the solution.

Different centre of pressure patterns within the golf stroke II: group-based analysis.

Although the golf coaching literature stresses the importance of weight transfer during the swing, research has been conflicting or lacking statistical support. A potential problem with previous studies is that no attempt was made to account for different movement strategies in the golf swing. This study evaluated the relationship between centre of pressure measures and club head velocity within two previously identified swing styles, the "Front Foot" and "Reverse" styles. Thirty-nine Front Foot golfers and 19 Reverse golfers performed swings with a driver while standing on two force plates. From the force plate data, centre of pressure displacement, velocity, range, and timing parameters were calculated. Correlation and regression analysis indicated that a larger range of centre of pressure and a more rapid centre of pressure movement in the downswing was associated with a larger club head velocity at ball contact for the Front Foot group. For the Reverse golfers, positioning the centre of pressure further from the back foot at late backswing and a more rapid centre of pressure transfer towards the back foot at ball contact was associated with a larger club head velocity at ball contact. This study has highlighted the importance of identifying different movement strategies before evaluating performance measures, as different parameters were found to be important for the Front Foot and Reverse styles.

The short golf backswing: effects on performance and spinal health implications.

BACKGROUND: Full recoil golf swings have been implicated in back pain and injury in golfers. Evidence suggests that a restricted backswing may reduce the potential for injury without compromising performance. OBJECTIVE: To examine both golf swing performance and selected muscular actions of the trunk and shoulder during a full recoil swing as compared with a modified short backswing. METHODS: Electromyographic (EMG) recordings were taken bilaterally from the lumbar, external oblique, latissimus dorsi, and right pectoral muscles in 7 golfers during a full recoil swing and a modified short backswing. High-speed videotape was used to measure back swing angle reduction. Clubhead velocity (CHV) and ball-contact accuracy were quantified by using a swing speed indicator and clubface contact tape, respectively. RESULTS: Shortening of the backswing by 46.5 degrees +/- 24.7 degrees had no effect on stroke accuracy as measured by mean deviation from the target spot on the club (19.0 +/- 7.8 mm vs 19.3 +/- 9.2 mm). CHV was not significantly reduced (33.9 +/- 2.5 m/s vs 31.2 +/- 2.2 m/s). However, EMG root-mean-square was decreased 19% in the right oblique muscle from 750 to 250 ms before impact (P < .05). During the acceleration phase, activation of left lumbar muscle decreased by 12%, whereas activation of right latissimus muscle increased by 21%. Although left lumbar muscle activity during the follow-through increased 14%, there was a substantial (17%) but nonsignificant decrease of activation of trunk muscles (P = .11). There was a general trend toward an increased activation of the shoulder musculature from 250 ms before impact to 500 ms after impact. CONCLUSION: These data support the idea that short backswings in golf may reduce trunk muscle activation and possibly reduce back injury and pain without negatively impacting swing accuracy or CHV. However, the short swing increases shoulder muscle activation and may, in turn, promote risk for shoulder injury.

Classification of errors in locating a rigid body.

This paper discusses the manner in which random Gaussian errors affect the determination of body segment kinematics. For the process of modelling rigid body (RB) motion, three types of kinematic errors, input, measured and theoretical, are identified. These correspond to errors in: the determination of three-dimensional observed points, the RB fit of those points, and the estimation of true RB positions, respectively. Of these, the theoretical error is most critical and most pivotal. Accuracy is provided when the theoretical error is minimised, yet only the measured error can be minimised by RB modelling algorithms. In computer simulations one may determine the effect that such manipulations have on theoretical error, yet in most experimental conditions this value may not even be calculated. Fortunately, computer simulations can be performed to determine the inter-relationships between types of RB modelling errors. Such simulations can also be used to investigate the effects of RB shape. In this paper, Monte Carlo simulations were performed on three unit radius RBs; a triangle, a square and a tetrahedron. Although the use of the triangle provided the lowest measured error, this also coincided with the greatest theoretical error. The use of redundant points was found to yield superior theoretical accuracies. A slight advantage was gained with use of the non-planar point arrangement on the tetrahedron, both the measured and theoretical errors were reduced. Finally, the superiority of RB modelling over individual point tracking was reflected in all of the results; between 33 and 50% of the input error was eliminated with the use of RB modelling.

The basics of laser technology.

As the use of laser systems increases, the nurse must be able to cope with the many changes that this new technology brings. An understanding of laser biophysics provides a foundation for laser safety. The nurse must also be aware of the organizational elements needed to provide a comprehensive laser program. Laser technology has definitely revolutionized modern health care delivery, and the nurse is instrumental in the continuing advancement of this science.

Effect of load, cadence, and fatigue on tibio-femoral joint force during a half squat.

Ten male university student volunteers were selected to investigate the 3D articular force at the tibio-femoral joint during a half squat exercise, as affected by cadence, different barbell loads, and fatigue. Each subject was required to perform a half squat exercise with a barbell weight centered across the shoulders at two different cadences (1 and 2 s intervals) and three different loads (15, 22 and 30% of the one repetition maximum). Fifty repetitions at each experimental condition were recorded with an active optoelectronic kinematic data capture system (WATSMART) and a force plate (Kistler). Processing the data involved a photogrammetric technique to obtain subject tailored anthropometric data. The findings of this study were: 1) the maximal antero-posterior shear and compressive force consistently occurred at the lowest position of the weight, and the forces were very symmetrically disposed on either side of this halfway point; 2) the medio-lateral shear forces were small over the squat cycle with few peaks and troughs; 3) cadence increased the antero-posterior shear (50%) and the compressive forces (28%); 4) as a subject fatigues, load had a significant effect on the antero-posterior shear force; 5) fatigue increased all articular force components but it did not manifest itself until about halfway through the 50 repetitions of the exercise; 6) the antero-posterior shear force was most affected by fatigue; 7) cadence had a significant effect on fatigue for the medio-lateral shear and compressive forces.