Comparing the pre- and post-impact ball and racquet kinematics of elite tennis players' first and second serves: a preliminary study   总被引：1，自引：0，他引：1  

Chow JW  Carlton LG  Lim YT  Chae WS  Shim JH  Kuenster AF  Kokubun K 《Journal of sports sciences》2003,21(7):529-537

The aim of this study was to compare the pre- and post-impact three-dimensional kinematics of the ball and racquet during first and second serves performed by elite tennis players. Data were collected from four male and four female right-handed professional players during competition using two high-speed cameras (200 Hz). For each player, one first serve and one second serve from the 'deuce' or right service court that landed within the specified target area were analysed. To test for significant differences between the first and second serves, Wilcoxon tests (P < or = 0.05) were performed on selected parameters. The results indicate that the ball travelled forward and to the left during the flight phase of the toss in all but one trial. The average pre-impact ball forward location for the first serve was significantly more in front and had a higher associated forward ball velocity than the corresponding values for the second serve. On average, the decrease in post-impact ball speed from the first to the second serve was 24.1%. No significant differences between the first and second serves were found in the pre-impact racquet head speed and orientation, which was represented as a unit vector perpendicular to the racquet face. The major adjustments made by the players when going from the first to second serve were a decrease in pre-impact ball forward location (P < or = 0.01) and an increase in the pre-impact racquet vertical and lateral velocities (both P < or = 0.05). This implies that the players tossed the ball closer to the body and imparted topspin and sidespin on the ball by changing the racquet vertical and lateral velocities when going from the first to the second serve.  相似文献   

Chronic flexibility gains: effect of isometric contraction duration during proprioceptive neuromuscular facilitation stretching techniques     

Rowlands AV  Marginson VF  Lee J 《Research quarterly for exercise and sport》2003,74(1):47-51

The aim of this study was to assess the effect of to isometic contraction durations during propiceptive neuromuscular facilitation stretching on gains inflexion at the hip. Forty-three women (M age = 20.0 years, SD = 1.3) were assigned to one of three groups: 5-s isometric contraction (5-IC), 10-IC, and control. Flexibility was assessed at baseline and Weeks 3 and 6. Analysis of covariance, controlling for pretest differences, showed a significant interaction, F(2, 33) = 44.1, p < .001. Flexibility was significant lower in the control group relative to the 5-IC and 10-IC groups and in the 5-IC group relative to the 10-IC group at 3 and 6 weeks (3 weeks = 101.2 +/- 1.4 degrees, 114.3 +/- 1.5 degrees, 120.5 +/- 1.3 degrees; 6 weeks = 103.0 +/- 1.4 degrees, 126.1 +/- 1.6 degrees, 133.3 +/- 1.4 degrees for control, 5-IC and 10-IC groups, respectively). A longer contraction time led to greater increases in flexibility.  相似文献   

Book Reviews     

Olivia Remie Constable  Eleanor A. Congdon  Andrew J. Lane  Sharon E. J. Gerstel  Ann Chamberlin  G.A. Loud 《Al-Masaq: Islam & the Medieval Mediterranean》2007,19(2):199-215

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The Psychology of the Week‐Day Religious School     

E. Leigh Mudge 《Religious education (Chicago, Ill.)》2013,108(6):305-307

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Feedback complexity and corrective efficiency     

Raymond W. Kulhavy  Mary T. White  Bruce W. Topp  Ann L. Chan  James Adams 《Contemporary educational psychology》1985,10(3):285-291

College undergraduates read a 2400-word passage, responded to 16 multiple-choice questions, and received one of four types of feedback following their responses. Complexity of feedback was inversely related to both error correctability and criterion efficiency taken as a ratio of feedback study time to post-test corrects. The results were discussed in terms of depth of processing and instructional comprehension.  相似文献   

Editorial: NATE the Sum of its Parts     

Ann Shreeve 《English in Education》1998,32(2):1-3

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Editorial     

Ann Shreeve 《English in Education》1990,24(3):1-2

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Confounding compression: the effects of posture,sizing and garment type on measured interface pressure in sports compression clothing     

Ned Brophy-Williams  Matthew William Driller  Cecilia Mary Shing  James William Fell  Shona Leigh Halson 《Journal of sports sciences》2015,33(13):1403-1410

The purpose of this investigation was to measure the interface pressure exerted by lower body sports compression garments, in order to assess the effect of garment type, size and posture in athletes. Twelve national-level boxers were fitted with sports compression garments (tights and leggings), each in three different sizes (undersized, recommended size and oversized). Interface pressure was assessed across six landmarks on the lower limb (ranging from medial malleolus to upper thigh) as athletes assumed sitting, standing and supine postures. Sports compression leggings exerted a significantly higher mean pressure than sports compression tights (P < 0.001). Oversized tights applied significantly less pressure than manufacturer-recommended size or undersized tights (P < 0.001), yet no significant differences were apparent between different-sized leggings. Standing posture resulted in significantly higher mean pressure application than a seated posture for both tights and leggings (P < 0.001 and P = 0.002, respectively). Pressure was different across landmarks, with analyses revealing a pressure profile that was neither strictly graduated nor progressive in nature. The pressure applied by sports compression garments is significantly affected by garment type, size and posture assumed by the wearer.  相似文献   

Child and Adolescent Predictors of Personality in Early Adulthood          下载免费PDF全文

Maria Wängqvist  Michael E. Lamb  Ann Frisén  C. Philip Hwang 《Child development》2015,86(4):1253-1261

This study investigated development of the Big Five personality traits from early childhood into adulthood. An initial group of 137 Swedish children were assessed eight times between ages 2 and 29 years. Initial decreases in extraversion leveled off in early adulthood; agreeableness and conscientiousness increased from ages 2 to 29; neuroticism initially increased, leveled off in later childhood and adolescence, and decreased throughout early adulthood; while openness to experience showed an initial increase, then decreased and leveled off in early adulthood. Individual developmental trajectories varied significantly, particularly in relation to gender. Personality traits became increasingly stable, and the fact that childhood scores predicted scores in adulthood indicated that personalities are fairly stable across this portion of the life span.  相似文献   

Investigating Microadaptation in One-to-One Human Tutoring     

Stephanie Ann Siler  Kurt VanLehn 《Journal of Experimental Education》2015,83(3):344-367

The authors investigated whether some advantages of tutoring over other instructional methods are due to microadaptation, or, tutors basing their actions on assessments of tutees they develop during tutoring. In a 2 × 2 between-subjects experiment, independent variables were shared experience (tutors either worked with the same or a different tutee in each of four segment of the tutoring session) and communication context (face-to-face or computer-mediated). Although there were no overall learning differences across experience conditions, tutees who worked with the same tutor demonstrated better learning of concepts initially discussed during the final tutoring segment. Shared experience led to accurate competence assessments only in the computer-mediated context, suggesting that cognitive load influences assessment development. However, there was no evidence of micro-adaptation.  相似文献