Dynamics of the martial arts high front kick

Fast unloaded movements (i.e. striking, throwing and kicking) are typically performed in a proximo‐distal sequence, where initially high proximal segments accelerate while distal segments lag behind, after which proximal segments decelerate while distal segments accelerate. The aims of this study were to examine whether proximal segment deceleration is performed actively by antagonist muscles or is a passive consequence of distal segment movement, and whether distal segment acceleration is enhanced by proximal segment deceleration. Seventeen skilled taekwon‐do practitioners were filmed using a high‐speed camera while performing a high front kick. During kicking, EMG recordings were obtained from five major lower extremity muscles. Based on the kinematic data, inverse dynamics computations were performed yielding muscle moments and motion‐dependent moments. The results indicated that thigh deceleration was caused by motion‐dependent moments arising from lower leg motion and not by active deceleration. This was supported by the EMG recordings. Lower leg acceleration was caused partly by a knee extensor muscle moment and partly by a motion‐dependent moment arising from thigh angular velocity. Thus, lower leg acceleration was not enhanced by thigh deceleration. On the contrary, thigh deceleration, although not desirable, is unavoidable because of lower leg acceleration.     

Information recall of younger and older skilled athletes: The role of display complexity,attentional resources and visual exposure duration

This study was concerned with the interactive role of experience of athletic skill with other relevant environmental variables (display complexity, attentional resources, exposure time of stimuli) on perception (recall) of structured handball game situations. Nineteen experienced (older) and 19 less experienced (younger) handball players were assigned randomly either to ball‐bouncing (diverted attention) or to calm seated (focused attention) conditions. In each of the two conditions, the subjects were exposed to a total of 36 slides containing 2–3, 5–6 and 8–10 players. Eighteen slides were exposed for 0.5 s and 18 for 1.0 s. All the slides contained structured defence and offence situations. Recall scores were subjected to repeated‐measures ANOVA using attention condition and age as between‐subject factors and task complexity and exposure duration as within‐subject factors. The results showed that the recall of less experienced players deteriorated more than the recall of more experienced players following exposure to complex displays (≥ 8 players) while engaging in a secondary task (bouncing). The findings suggest that research paradigms should be applied in the field of sport which share both ecological validity and a potential to discover the cognitive substrates underlying experience and age in skilled motor performance.     

Age Differences in use of Strategy for Recall of Movement in a Large Scale Environment

Abstract

In order to investigate how children remember distance (route) and location (landmark) information, two experiments were conducted in a large scale environment using jogging as the means of locomotion. In Experiment 1, thirty 4-year-old and thirty 9-year-old children were randomly assigned within age to three groups which were cued prior to the jog to remember the event, location of the event or distance to the event. Results indicated that older children reproduced the location and distance better than younger children. Cueing children to remember the location resulted in more accurate estimates than the other conditions. In Experiment 2, 5-year-old, 9-year-old, and 12-year-old children (24 children of each age) were randomly divided into step counting strategy and control groups, and asked to reproduce a criterion distance jogged. Results indicated that the three strategy groups and the 12-year-old controls estimated distance with similar accuracy, but the 9- and 5-year-old controls were different, as their error was inversely related to age.     

Introduction

Abstract

Information systems design can progress toward meeting the needs of the population of decision‐makers, managers, policy‐makers, and interdisciplinary workers by attention to specifications obtained from the user's situation. The user situation is represented by problems and their component dimensions, of which subject is only one dimension. The other problem dimensions, which relate to information traits, are discussed for the purpose of proposing a new orientation for the design of information systems.     

Why users keep answering questions in online question answering communities: A theoretical and empirical investigation

This study theorized and validated a model of knowledge sharing continuance in a special type of online community, the online question answering (Q&A) community, in which knowledge exchange is reflected mainly by asking and answering specific questions. We created a model that integrated knowledge sharing factors and knowledge self-efficacy into the expectation confirmation theory. The hypotheses derived from this model were empirically validated using an online survey conducted among users of a famous online Q&A community in China, “Yahoo! Answers China”. The results suggested that users’ intention to continue sharing knowledge (i.e., answering questions) was directly influenced by users’ ex-post feelings as consisting of two dimensions: satisfaction, and knowledge self-efficacy. Based on the obtained results, we also found that knowledge self-efficacy and confirmation mediated the relationship between benefits and satisfaction.     

Improved approaches to stability criteria for neural networks with time-varying delays

In this paper, the problem of stability analysis for neural networks with time-varying delays is considered. By the use of a newly augmented Lyapunov functional and some novel techniques, sufficient conditions to guarantee the asymptotic stability of the concerned networks are established in terms of linear matrix inequalities (LMIs). Three numerical examples are given to show the improved stability region of the proposed works.     

Carl Rogers,learning and educational practice: critical considerations and applications in sports coaching

Discussions about ‘athlete-centered’ coaching and ‘coach-centered’ coach education have started to gain increasing popularity in the field of coaching science. While it has been suggested that these ‘learner-centered’ approaches arguably align with the theoretical ideals of humanistic psychology, an in-depth examination of the implications of this learning orientation to sports coaching remains elusive. Rather, discussions have tended to be detached from theory, focusing instead on practices and methods. In light of this development, the present paper provides a detailed and critical overview of one of the leading humanistic thinkers' work, namely Carl Rogers, in order to consider what implications his theorising about ‘person-centered’ learning could have for the development of athletes and coaches. In doing so, we hope that this article will serve to advance understanding and theoretically underpin what have tended to be largely a-theoretical and superficial discussions about ‘athlete-centered’ coaching and ‘coach-centered’ coach education.     

Influence of a critically oriented methods course and early field experience on preservice teachers' conceptions of teaching

In recent years there has been a growing interest in arming physical education teachers with critical pedagogies. The purpose of this study was to determine the influence of a critically oriented methods course and early field experience (EFE) on 20 preservice teachers' (PTs) conceptions of the teaching–learning process. Data were collected using the critical incident technique and a reflective questionnaire. They were analyzed by employing the analytic induction method. Results indicated that the inward focus of the methods course and EFE on the analysis of teaching had a considerable influence on the PTs. Conversely, the outward focus on curriculum studies as well as four permeating themes (elitism, racism, classism, and sexism) appeared to have virtually no impact on them at all. Possible reasons for and implications of these findings are discussed.     

Aerodynamic effects on the accuracy of an end-over-end kick of an American football

The effects of initial conditions on the flight of an American football kicked in an end-over-end manner were investigated using a dynamic simulation employing the quaternion method. The effects of initial tilt and spin about the longitudinal axis of the ball were considered. For the most accurate kick, our simulations show that the ball should be vertical leaving the kicker’s foot, and have no angular velocity about the longitudinal axis of the ball. A case study was performed for which experimental data were available, showing the trends of the flight of the ball captured in our simulations in actual game situations.     

Community Languages and Anti‐racist Education: the open battlefield

The shift from a multicultural to an anti‐racist perspective in education left the issue of community languages aside. There seem to be four reasons for the persisting marginal position of community languages within anti‐racist education in Britain: (1) the gap between the theoretical concept of anti‐racist education and its implementation in practice; (2) the prevalent mainstream doctrine; (3) the pervasive international hegemony of English language; and (4) the political devaluation of ethnicity approaches. The 1988 United Kingdom Education Reform Act, along with the European integration and its accompanying Eurocen‐trism, appears to marginalise the community languages even further.