Ground reaction forces,kinematics, and muscle activations during the windmill softball pitch     

Gretchen D. Oliver  Hillary Plummer 《Journal of sports sciences》2013,31(10):1071-1077

Abstract

The aims of the present study were to examine quantitatively ground reaction forces, kinematics, and muscle activations during the windmill softball pitch, and to determine relationships between knee valgus and muscle activations, ball velocity and muscle activation as well as ball velocity and ground reaction forces. It was hypothesized that there would be an inverse relationship between degree of knee valgus and muscle activation, a direct relationship between ground reaction forces and ball velocity, and non-stride leg muscle activations and ball velocity. Ten female windmill softball pitchers (age 17.6 ± 3.47 years, stature 1.67 ± 0.07 m, weight 67.4 ± 12.2 kg) participated. Dependent variables were ball velocity, surface electromyographic (sEMG), kinematic, and kinetic data while the participant was the independent variable. Stride foot contact reported peak vertical forces of 179% body weight. There were positive relationships between ball velocity and ground reaction force (r = 0.758, n = 10, P = 0.029) as well as ball velocity and non-stride leg gluteus maximus (r = 0.851, n = 10, P = 0.007) and medius (r = 0.760, n = 10, P = 0.029) muscle activity, while there was no notable relationship between knee valgus and muscle activation. As the windmill softball pitcher increased ball velocity, her vertical ground reaction forces also increased. Proper conditioning of the lumbopelvic–hip complex, including the gluteals, is essential for injury prevention. From the data presented, it is evident that bilateral strength and conditioning of the gluteal muscle group is salient in the windmill softball pitch as an attempt to decrease incidence of injury.  相似文献   

Comparison of pitching kinematics between youth and adult baseball pitchers: a meta-analytic approach     

Jason Wicke  David W. Keeley  Gretchen D. Oliver 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(4):315-323

Coaches teach proper mechanics at a young age in an effort to increase pitching efficiency (i.e., proper pitching mechanics). Unfortunately, the mechanics taught to beginning pitchers are based on the findings from adult pitchers and may result in techniques that are detrimental to younger pitchers. The purpose of this study was to compare kinematics published for pitchers across various ages in an effort to determine whether the pitching techniques vary across developmental periods. A meta-analysis of papers published describing pitching kinematics for youth and adult pitchers was conducted. Maximal rotational velocity of the trunk and maximum external rotation of the shoulder were observed during the arm cocking phase. Peak magnitudes for abduction, horizontal adduction, and shoulder internal rotation were observed during the deceleration phase of the movement. In addition, by comparing previously published data across youth and adult pitchers, valuable insight into the differences in mechanics was gained. The results demonstrated that there are some distinct differences between youth and adult pitching mechanics. This finding may allow increased focus to be applied to those parameters observed to differ across age, increasing the knowledge base available for coaches to properly instruct youth pitchers.  相似文献   

Adaptive processes of coping,defending and mastery     

Robert H. Short  Gretchen C. Hess 《International journal for the advancement of counseling》1983,6(3):201-217

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Computer microworlds and reading: An analysis for their systematic application     

Robert W. Lawler  Gretchen P. Lawler 《Instructional Science》1986,14(3-4):255-275

Learning can be seen as a consequence of problem solving in particular cases. It occurs when one achieves a solution which is able to be used later. Anchoring with variation is a common and important process, providing a framework through which one can discuss coping with something imperfectly understood in terms of what is already well known. Our purpose in the following discussion is to explore some possible implications of this process for reading education as a worked example of how educational technology presents us with an opportunity for reconceptualizing instruction.English has the phonological potential for more than 60 thousand monosyllables. Our analysis asks how many monosyllabic words exist in fact and what organization can be imposed on them to make the phonological code more accessible. We've chosen to represent these monosyllables as an initial phonemic cluster plus residue. The most common 550 residues cover 73 percent of the existing 7000 monosyllables. If children can learn 550 different correspondences between sounds and spelling patterns, their knowledge of these words, coupled with the ability to modify interpretations of letter strings by anchoring with variation, will cover a major portion of the phonetic-orthographic correspondences of the English language. We believe this extensive, concrete foundation of word and sound knowledge will permit children to read well enough that instruction will become primarily a refining and perfection of such knowledge.The primary design conclusion is that, if we create computer-based microworlds using words with the most common residues as the names for their entities and their actions, we will be providing a set of systematically generated monosyllabic anchors which promises to be highly effective for children's interpretation of many words they will encounter in reading English. The potential revolutionary impact of such a prereading curriculum is worth exploring.  相似文献   

Doubling Down: President Barack Obama’s Doubled Persona after the Zimmerman Verdict     

Roger C. Aden  Kelsey Crowley  Erin Phillips  Gretchen Weger 《Communication Studies》2016,67(5):605-622

This article analyzes President Barack Obama’s remarks following the acquittal of George Zimmerman on the charge of murdering Trayvon Martin. Speaking directly to, for, or about African Americans would lead some to accuse him of speaking primarily as a black man, while ignoring the idea of race would lead some to accuse him of failing to acknowledge its omnipresence in American life. To manage these constraints, the president employed what we have termed a doubled persona; that is, he enacted two different speaking personae and envisioned a distinct audience persona for each speaking persona: He spoke both as a black president and as a president who is black.  相似文献   

Internet Resources for Middle School Science: Golden Opportunity or “Silicon Snake Oil”?     

Jackson  David F.  Bourdeau  Gretchen  Sampson  Alice  Hagen  Thomas J. 《Journal of Science Education and Technology》1997,6(1):49-57

This study examines the experiences of six teachers at three schools in learning about and beginning to implement or enhance project-based learning in their middle school science classrooms using a variety of resources available through the Internet. Data were gathered over a one-year period ending in March, 1996. As a result of their experience, teachers became aware of the possibilities and the problems created by both the nearly unlimited quantity of information available on the Internet and the limited quality and relevance of much of that information. Positive and negative experiences described by teachers and the variety of issues and concerns which they reflect are compared and contrasted, including: unreliability of network connections; potential availability to students of inappropriate resources; consistency of classroom organization structures necessary to facilitate Internet access with normally preferred teaching methods; the dependence of the efficiency and motivational value of project-based units on students' appreciation of the nature and power of the technology; conflict between curriculum space devoted to teaching about technology and that devoted to substantively using the technology to teach about science and related subjects; the on call convenience of the Internet; the up-to-date nature of much of the scientific information available on the Internet; Internet-based information (versus textbook information) as authoritative yet not impersonal.  相似文献   

Multiple-transfer students in a public urban university: Background characteristics and interinstitutional movements   总被引：1，自引：1，他引：1  

Gretchen Warner Kearney  Barbara K. Townsend  Terrence J. Kearney 《Research in higher education》1995,36(3):323-344

Little research has been conducted on multiple-transfer students, those students who transfer more than once during their collegiate careers. In this study, background characteristics and previous interinstitutional movements of a sample of multiple transfers enrolled at a large, urban, public university were examined. These students moved along four different transfer paths before enrolling at the university, where they comprised one-fifth of new undergraduate enrollments. Their paths differed significantly on a number of demographic, institutional, and interaction variables. Overall, these students were academic achievers with high socioeconomic status backgrounds, who focused on academic quality and programs in choosing four-year colleges. Their tendency to transfer among large, inexpensive, public institutions has negative implications for the private sector of higher education.  相似文献   

“Social Work Is a Profession,Not an Ideology”: A Qualitative Analysis of Student Perceptions of Social Justice Discussions in the Classroom     

Candace Hansford  Gretchen E. Ely  Chris Flaherty  Nancy Meyer-Adams 《Journal of Teaching in Social Work》2017,37(3):199-217

The purpose of this article is to describe student perceptions of their experiences around social justice discussions in the social work classroom through a qualitative, grounded theory framework. Student responses from a qualitative section of a survey were analyzed and sorted into three categories: perceived discrimination, heightened self-awareness/self-assessment, and future social work practice. Each of these categories was derived from comparable multiple themes stemming from the student responses. A conceptual model resulting from the analysis suggests that students who shared experiences of perceived discrimination during classroom discussions could develop an enhanced self-awareness, which would result in an added empathy for clients in their future social work practice. Suggestions for teaching strategies and directions for future research are also discussed.  相似文献   

Validity and reliability of a computer-vision-based smartphone app for measuring barbell trajectory during the snatch     

Carlos Balsalobre-Fernández  Gretchen Geiser  John Krzyszkowski  Kristof Kipp 《Journal of sports sciences》2020,38(6):710-716

ABSTRACT

The purpose of this study was to investigate the validity of a smartphone app to measure biomechanical barbell parameters during the snatch. Ten collegiate NCAA division I athletes performed two repetitions each at 40, 50, 60, 70, and 80% of their 1-repetition maximum snatch. Barbell motions were simultaneously recorded with a motion capture system and the smartphone app. The motion capture system recorded the 3-D position of a reflective marker attached to the end of the barbell while the smartphone app was used to record sagittal plane video and track the shape of the weight plate from which the barbell center was derived. Peak forward (PFD) and backward (PBD) displacements and peak vertical displacement (PVD) and velocity (PVV) were calculated from both sets of data. Significant, strong to very strong Pearson’s product-moment correlation coefficients between both systems were noted for all parameters (r = 0.729–0.902, all p < 0.001). Small significant biases between systems were observed for PVD (ES = 0.284, p < 0.001) and PFD (ES=0.340, p < 0.01), while trivial to small, non-significant biases were observed for PBD (ES = 0.143) and PVV (ES = –0.100). Collectively, the results suggest that the app can provide biomechanical data of barbell motions similar to a 3-D motion capture system.  相似文献   

The Chicago Manual of Style,Seventeenth Edition     

Gretchen Webster 《Publishing Research Quarterly》2017,33(4):495-496

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