The influence of club-head kinematics on early ball flight characteristics in the golf drive     

Matthew Sweeney  Peter Mills  Jacqueline Alderson  Bruce Elliott 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(3):247-258

Despite many coaching and biomechanical texts describing how the kinematics of the club-head at impact lead to distance and accuracy of the ball flight, there is limited quantitative evidence supporting these assertions. The purpose of this study was to quantify the relationships between club-head kinematics and subsequent early ball flight characteristics during the golf drive. An opto-reflective system operating at 400 Hz was used to capture the swings of 21 male golfers using their own drivers. The 3D displacement data permitted the calculation of club-head kinematics at impact, as well as subsequent early ball flight characteristics. Using regression analyses, club-head kinematics at impact (velocity, orientation, path, and centeredness) were used to explain the variability in five dependent variables of early ball flight characteristics (resultant velocity, launch angle, side angle, back spin, and side spin). The results of the study indicated that club-head kinematics at impact explained a significant proportion of early ball flight characteristics (adjusted r ² = 0.71–0.82), even when generalized across individual clubs.  相似文献   

Effect of skill decomposition on racket and ball kinematics of the elite junior tennis serve     

Machar Reid  Bruce Elliott 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(4):296-303

Whole body kinematics of the tennis serve have been reported extensively in the literature, yet comparatively less information exists regarding the kinematic characteristics of the swing and toss. In attempting to develop consistency in placement of the toss and racket trajectory, coaches will often decompose the serve and practice it in separate parts. A 22-camera VICON MX motion analysis system, operating at 250 Hz, captured racket, ball and hand kinematics of the serves of five elite junior players under three conditions. The conditions were flat first serves (FS) directed to a 1 × 1 m target bordering the ‘T’ of the deuce service box, a ball toss (BT) in isolation and a free swing (SW) in isolation. Players were instructed to perform BT and SW as in the FS. Paired t-tests assessed within-group differences in hand, racket and ball kinematics between the discrete skill and the two decomposed conditions. Vertical displacement of the ball at its zenith increased significantly during BT compared with the FS and temporal associations between racket and ball motion during the FS (r = 0.861) were affected during task decomposition. This study questions the pervasive use of task decomposition in the development of the tennis serve.  相似文献   

A biomechanical comparison of the topspin and backspin forehand approach shots in tennis     

Bruce Elliott  Tony Marsh 《Journal of sports sciences》2013,31(3):215-227

Three‐dimensional (3‐D) high‐speed cinematographic techniques were used to record topspin and backspin forehand approach shots hit down‐the‐line by high‐performance players. The direct linear transformation (DLT) technique was used in the 3‐D space reconstruction from 2‐D images recorded via laterally placed phase‐locked cameras operating at 200 Hz. A Mann‐Whitney U‐test was calculated for the different aspects of the topspin and backspin shots to test for significance (P<0.05).

A significant difference was recorded between topspin and backspin shots in the angle of the racket at the completion of the backswing. The racket was taken 0.48 rad past a line drawn perpendicular to the back fence for topspin trials, but only rotated 0.86 rad from a line parallel to the net in the backspin shot. Maximum racket velocities occurred prior to impact and were significantly higher in topspin (26.5 m s‐¹) compared to backspin (16.6 m s^‐1) trials. This resulted in the topspin trials recording a significantly higher ball velocity compared to backspin trials (27.6 m s^‐1 vs 21.7 m s^‐1). Pre‐impact racket trajectories revealed that in topspin shots the racket moved on an upward path of 0.48 rad while in backspin shots it moved down at an angle of 0.34 rad. In the topspin trials impact occurred significantly further forward of the front foot than in backspin shots (0.26 m vs 0.05 m) while the angle of the racket was the same for both strokes (0.14 rad behind a line parallel to the net). The mean angle of the racket‐face at impact was inclined backwards by 0.11 rad for backspin strokes and rotated forward by 0.13 rad for topspin strokes. Angles of incidence and reflection of the impact between the ball and the court showed that backspin trials had larger angles of incidence and reflection than topspin strokes.  相似文献   

Long-axis rotation: The missing link in proximal-to-distal segmental sequencing     

R. N. Marshall  B. C. Elliott 《Journal of sports sciences》2013,31(4):247-254

Most assessments of segmental sequencing in throwing, striking or kicking have indicated a proximal-to-distal sequencing of end-point linear speeds, joint angular velocities, segment angular velocities and resultant joint moments. However, the role of long-axis rotations has not been adequately quantified and located in the proximal-to-distal sequence. The timing and importance of pronation-supination in the development of racquet head speed have been examined in the tennis serve and squash forehand drive and considered in relation to conventional concepts of proximal-to-distal sequencing. Both long-axis rotations reached their peak angular speeds late in both strokes, typically after shoulder flexion-extension, shoulder abduction-adduction and elbow extension. These results clarify and confirm the importance of upper limb long-axis rotations in the production of racquet head speed. It appears that traditional proximal-to-distal sequencing concepts are inadequate to describe accurately the complexity of the tennis serve or squash forehand drive. It is essential to consider upper arm and forearm longitudinal axis rotations in explaining the mechanics of these movements and in developing coaching emphases, strength training schedules and injury prevention programmes.  相似文献   

The penalty throw in water polo: A cinematographic analysis     

Bruce C. Elliott  Julie Armour 《Journal of sports sciences》2013,31(2):103-114

Three‐dimensional (3‐D) high‐speed cinematography was used to record the penalty throw in water polo by six elite male (M) and six elite female (F) players. The direct linear transformation technique (DLT) was used in the 3‐D space reconstruction from 2‐D images recorded via laterally placed phase‐locked cameras operating at 200 Hz. Five of the twelve subjects lifted the ball from underneath at the start of the throw whilst the remaining subjects opted for a rotation lift. As the ball was brought behind the head the females used very little hip and shoulder rotation compared to the male players so that four of the six female subjects were square on to the target at the rear point. At the completion of the backswing the wrist was flexed to a similar angle (M‐162°; F‐158°); the elbow angle showed significantly greater flexion for females (85°) than males (107°).

During the forward swing, from rear point to release, the wrist joint of the female players flexed from a rear point angle of 158° to 148° at release. The wrist movement for male subjects was different from the females in that it flexed from 162° to 147°, 0.10 s prior to release and then extended to 159° at palmar release before again flexing to 156° at release. The amount of elbow extension during the forward swing was 48° for both groups; however, the females actually released the ball with the forearm vertical (89°) compared to the male forearm angle of 78°. Maximum angular velocity of the wrist and elbow occurred at release for 9 of the 12 subjects. Both the wrist and elbow joints (F‐148°; M‐156° at wrist and F‐126°; M‐148° at elbow) demonstrated greater flexion at release in female subjects, compared with males. Maximum linear endpoint velocities for the forearm and hand segments occurred at ball release resulting in mean ball velocities of 19.1 m s ^‐1 and 14.7 m s^{‐ 1} for male and female subjects respectively.  相似文献   

Prevalence and psychological sequelae of self-reported childhood physical and sexual abuse in a general population sample of men and women     

Briere J  Elliott DM 《Child abuse & neglect》2003,27(10):1205-1222

OBJECTIVE: This study examined the prevalence and psychological sequelae of childhood sexual and physical abuse in adults from the general population. METHOD: A national sampling service generated a geographically stratified, random sample of 1,442 subjects from the United States. Subjects were mailed a questionnaire that included the Traumatic Events Survey (TES) [Traumatic Events Survey, Unpublished Psychological Test, Harbor-UCLA Medical Center, Los Angeles] and the Trauma Symptom Inventory (TSI) [Trauma Symptom Inventory Professional Manual, Psychological Assessment Resources, Odessa, FL]. Of all potential subjects, 935 (64.8%) returned substantially completed surveys. RESULTS: Sixty-six men and 152 women (14.2% and 32.3%, respectively) reported childhood experiences that satisfied criteria for sexual abuse, and 103 males and 92 females (22.2% and 19.5%, respectively) met criteria for physical abuse. Twenty-one percent of subjects with one type of abuse also had experienced the other type, and both types were associated with subsequent adult victimization. After controlling for demographics, adult history of interpersonal violence, and other child abuse, childhood sexual abuse was associated with all 10 scales of the TSI, and physical abuse was related to all TSI scales except those tapping sexual issues. Sexual abuse predicted more symptom variance than did physical abuse or adult interpersonal victimization. Various aspects of both physical and sexual abuse experiences were predictive of TSI scores. Abuser sex, however, both alone and in interaction with victim sex, was not associated with additional TSI symptomatology. CONCLUSIONS: Childhood sexual and physical abuse is relatively common in the general population, and is associated with a wide variety of psychological symptoms. These relationships remain even after controlling for relevant background variables.  相似文献   

Goal orientations in Russian university students: from mastery to performance?     

Richard Remedios  Zoya Kiseleva  Joe Elliott 《教育心理学》2008,28(6):677-691

Research in the UK has shown that students start their university career with the goal of mastering their subject, but this focus shifts as they progress through their degree program. Studies have suggested that unlike students in the UK, Russian students continue to take a strong mastery approach to their work. The main aim of this study was to assess whether the effects observed in UK studies could be found in a Russian context. In a cross‐sectional study, 618 students across four years of a degree program in a Russian university completed an achievement‐goal questionnaire. Results revealed patterns similar to the studies in the UK; Russian students’ levels of mastery were significantly lower after Year 1. The results are discussed in terms of potential changes in Russian culture. Methodological issues relating to the relative failure of some questionnaire items to validate fully within their hypothesised constructs are also discussed.  相似文献   

Differential Ability Scales – Second Edition (neuro)psychological predictors of math performance for typical children and Children with Math Disabilities     

James B. Hale  Catherine A. Fiorello  Ron Dumont  John O. Willis  Christopher Rackley  Colin Elliott 《Psychology in the schools》2008,45(9):838-858

Concerns about the ability‐achievement discrepancy method for specific learning disability (SLD) determination led to alternative research‐based methods, such as failure to respond to intervention. Neither of these regulatory methods address the statutory SLD definition, which explicitly includes a deficit in basic psychological processes. Examining neuropsychological processing differences among typical children and children with math SLD, commonality analyses revealed that Differential Ability Scales – Second Edition (DAS‐II) predictors accounted for more achievement variance in typical children (46% to 58%) than in children with math SLD (33% to 50%), with substantial loss of predictive validity when General Conceptual Ability was used instead of subcomponent scores. Results suggest that differences in typical predictor‐outcome relationships may provide a foundation for developing specific cognitive and academic interventions for children with math SLD. © 2008 Wiley Periodicals, Inc.  相似文献   

Evaluating the validity of the Automated Working Memory Assessment     

Tracy P. Alloway  Susan E. Gathercole  Hannah Kirkwood  Julian Elliott 《教育心理学》2008,28(7):725-734

The aim of the present study was to investigate the construct stability and diagnostic validity of a standardised computerised tool for assessing working memory: the Automated Working Memory Assessment (AWMA). The purpose of the AWMA is to provide educators with a quick and effective tool to screen for and support those with memory impairments. Findings indicate that working memory skills in children with memory impairments are relatively stable over the course of the school year. There was also a high degree of convergence in performance between the AWMA and the WISC‐IV Working Memory Index. The educational implications are discussed.  相似文献