Kinetic and kinematic analysis of stamping impacts during simulated rucking in rugby union     

Bodil Y Oudshoorn  Heather F Driscoll  Marcus Dunn  David James 《Journal of sports sciences》2018,36(8):914-919

Laceration injuries account for up to 23% of injuries in rugby union. They are frequently caused by studded footwear as a result of a player stamping onto another player during the ruck. Little is known about the kinetics and kinematics of rugby stamping impacts; current test methods assessing laceration injury risk of stud designs therefore lack informed test parameters. In this study, twelve participants stamped on an anthropomorphic test device in a one-on-one simulated ruck setting. Velocity and inclination angle of the foot prior to impact was determined from high-speed video footage. Total stamping force and individual stud force were measured using pressure sensors. Mean foot inbound velocity was 4.3 m ? s^?1 (range 2.1–6.3 m ? s^?1). Mean peak total force was 1246 N and mean peak stud force was 214 N. The total mean effective mass during stamping was 6.6 kg (range: 1.6–13.5 kg) and stud effective mass was 1.2 kg (range: 0.5–2.9 kg). These results provide representative test parameters for mechanical test devices designed to assess laceration injury risk of studded footwear for rugby union.  相似文献   

Threshold frequency of an electrically induced cramp increases following a repeated,localized fatiguing exercise     

Marcus B. Stone  Jeffrey E. Edwards  Kellie C. Huxel  Mitchell L. Cordova  Christopher D. Ingersoll  J. Patrick Babington 《Journal of sports sciences》2013,31(4):399-405

Abstract

Though clinical observations and laboratory data provide some support for the neuromuscular imbalance theory of the genesis of exercise-associated muscle cramps, no direct evidence has been published. The purpose of this study was to determine the effect of local muscle fatigue on the threshold frequency of an electrically induced muscle cramp. To determine baseline threshold frequency, a cramp was electrically induced in the flexor hallucis brevis of 16 apparently healthy participants (7 males, 9 females; age 25.1 ± 4.8 years). The testing order of control and fatigue conditions was counterbalanced. In the control condition, participants rested in a supine position for 30 min followed by another cramp induction to determine post-threshold frequency. In the fatigue condition, participants performed five bouts of great toe curls at 60% one-repetition maximum to failure with 1 min rest between bouts followed immediately by a post-threshold frequency measurement. Repeated-measures analysis of variance and simple main effects testing showed post-fatigue threshold frequency (32.9 ± 11.7 Hz) was greater (P < 0.001) than pre-fatigue threshold frequency (20.0 ± 7.7 Hz). An increase in threshold frequency seems to demonstrate a decrease in one's propensity to cramp following the fatigue exercise regimen used. These results contradict the proposed theory that suggests cramp propensity should increase following fatigue. However, differences in laboratory versus clinical fatiguing exercise and contributions from other sources, as well as the notion of a graded response to fatiguing exercise, on exercise-associated muscle cramp and electrically induced muscle cramp should be considered.  相似文献   

Effect of cluster set configurations on power clean technique     

Justin P. Hardee  Marcus M. Lawrence  Kevin A. Zwetsloot  N. Travis Triplett  Alan C. Utter 《Journal of sports sciences》2013,31(5):488-496

Abstract

The purpose of this investigation was to examine the effects of cluster set configurations on power clean technique. Ten male, recreational weightlifters performed three sets of six repetitions at 80% of one repetition max with 0 (P0), 20 (P20) or 40 seconds (P40) inter-repetition rest. During the first and second set of P0, the catch and first pull were in a more forward position during repetition 6 as compared to repetition 1, respectively. During the second set of P40, differences in horizontal displacement were found between repetitions 1 and 6 for the second pull and the loop. During the third set of P40, differences in horizontal displacement were found between repetitions 1 and 6 for the first pull, transition, and beginning of the second pull. No differences in horizontal displacement were found between repetitions 1 and 6 during P20. During each set of P0, vertical displacement decreased between repetitions 1 and 6 (1.02 ± 0.07 m vs. 0.94 ± 0.06 m; Mean ± s). Cluster set configurations led to the maintenance of vertical displacement throughout all sets. The results demonstrate cluster set configurations with greater than 20 seconds inter-repetition rest maintain weightlifting technique to a greater extent than a traditional set configuration.  相似文献   

Resource constraints as triggers of radical innovation: Longitudinal evidence from the manufacturing sector     

Marcus Matthias Keupp  Oliver Gassmann 《Research Policy》2013

Despite the significant role of radical innovation as a driver of firm growth and performance, the consequences of resource constraints for radical innovation outcomes remain unknown. Our paper addresses this gap. We combine arguments from entrepreneurship theory and the theory of recombinative innovation to construct an overarching theoretical framework that argues why resource constraints can promote, rather than impede, radical innovation. We then build hypotheses on two specific resource constraints, knowledge and financial, and test these by a lagged-variable random-effects Tobit model with longitudinal data from an exceptionally large and detailed innovation survey. Controlling for absorptive capacity, firm age, and firm growth, we find full support for the hypothesis that knowledge constraints spur radical innovation and partial support for the hypothesis that financial constraints spur radical innovation. We discuss the theoretical significance of these findings and point to managerial implications and paths for future research.  相似文献   

Kinematic differences of elite and high-performance tennis players in the cross court and down the line forehand     

Johannes Landlinger  Stefan Josef Lindinger  Thomas Stöggl  Herbert Wagner  Erich Müller 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(4):280-295

This study identified and compared the full body kinematics of different skill levels in the forehand groundstroke when balls were hit cross court and down the line. Forty-three three-dimensional retro-reflective marker trajectories of six elite and seven high-performance players were recorded using an eight-camera 400 Hz, Vicon motion analysis system. The six highest horizontal velocity forehands with reliable kinematics of all participants were analysed for each specific situation (a total of 156 analysed shots). Significant differences (p < 0.01) and large effect sizes were observed between elite and high-performance players in linear velocity of the shoulder (2.0 vs. 1.2 m/s), angular velocity of the pelvis (295 vs. 168 °/s), and angular velocity of the upper trunk (453 vs. 292 °/s) at impact. The elite group showed a tendency towards higher racquet velocities at impact (p < 0.05). No significant differences were found in angular displacement of the racquet, hip alignment, or shoulder alignment at the completion of the backswing; nor did angular displacement vary significantly at impact. Irrespective of the group, different shoulder, hip, and racquet angles were found at impact, depending on the situation. The results should assist coaches when striving to improve their players' forehand.  相似文献   

A comparison of the Rescorla-Wagner and Pearce models in a negative patterning and a summation problem     

Karyn M. Myers  Edgar H. Vogel  Jennifer Shin  Allan R. Wagner 《Learning & behavior》2001,29(1):36-45

In two experiments, we examined two related conditioning problems previously investigated by Red-head and Pearce (1995a) and Pearce, Aydin, and Redhead (1997). Experiment 1 involved an A+, B+, C+, AB+, AC+, BC+, ABC2 discrimination. The Rescorla-Wagner model predicts that response to AB, AC, and BC will be greater than that to A, B, and C at asymptote, whereas the Pearce model makes the opposite prediction. In Experiment 2, we investigated the responding to a novel ABC compound in groups trained with either A+, B+, C+ or AB+, AC+, BC+. The Rescorla-Wagner model predicts greater response to ABC in the group trained with A+, B+, C+ than in the group trained with AB+, AC+, BC+, whereas the Pearce model makes the opposite prediction. In contrast to the findings of Redhead and Pearce (1995a) and Pearce et al. (1997) in pigeon autoshaping, our findings in rabbit eyelid conditioning support the Rescorla-Wagner model.  相似文献   

Learning problems — when arts students encounter computer science     

Helge Dohn  K. D. Wagner 《Higher Education》1987,16(2):231-235

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Learner control of instructional sequencing within an adaptive tutorial CAI environment     

Robert J. Seidel  Harold Wagner  Richard D. Rosenblatt  Michael J. Hillelsohn  John Stelzer 《Instructional Science》1978,7(1):37-80

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Using Student Journals for Course Evaluation     

Zita M. Wagner 《Assessment & Evaluation in Higher Education》1999,24(3):261-272

The evaluation of courses has become more important than ever in the higher education sector. Information is commonly collected from students on their perceptions of a course using questionnaires, discussions or interviews. This paper discusses the use of a student learning journal as a means of collecting data on the effectiveness of a course. Students in a graduate diploma course at the University of Technology, Sydney use learning journals to record and reflect on their development as a teacher/trainer over one semester. The evaluator of the course obtains qualitative data from the journals regarding students’ perceptions of the course content, structure, activities and assessment. The main advantages of this technique include the longitudinal perspective it gives on students perceptions of a course and also that it provides information on the whole course, particularly on whether whole course outcomes are being met. Collecting information from student journals also has the advantage that the data were not written specifically for course evaluation. Issues regarding validity, confidentiality and data analysis using student journals are addressed in this paper as is the place of this technique in a quality assurance scheme for a course.  相似文献   

Exploring the relationship between school discipline referrals and delinquency     

Jeffery Sprague  Hill M. Walker  Steve Stieber  Brandi Simonsen  Vicki Nishioka  Linda Wagner 《Psychology in the schools》2001,38(2):197-206

There is a growing concern about violent and destructive behaviors of youth that require intervention by juvenile justice and youth‐serving agencies. This concern has led many to conclude that schools and community agencies must increase efforts to prevent juvenile delinquency and to provide programs that will facilitate rehabilitation, education, and vocational training for youth already involved. A clear understanding of the nature and range of behaviors that result in juvenile crime is needed in order to develop programs and interventions that can be expected to lead to beneficial changes for youth and for society as a whole. The purpose of this article is to describe the relationship between school behaviors and youth characteristics in school (e.g., discipline referrals, teacher nominations, nomothetic ratings) and referrals to juvenile authorities (e.g., illegal behaviors). We describe a strategy of using teacher nominations, school discipline referrals, and community arrest data to predict delinquent and violent behavior in youth. We outline data from a group of socially maladjusted middle school youth to illustrate the relationship between the two data sources and recommendations for identification and treatment of youth at risk for delinquency and antisocial behavior. © 2001 John Wiley & Sons, Inc.  相似文献