History and Singularity of Krav-Maga

Abstract

Krav-Maga (‘contact combat’) is an Israeli combat discipline practiced by thousands of individuals worldwide. During the past few decades, it has attracted a considerable amount of attention mainly as a self-defence system, although its origins are also rooted in sport. Despite the widespread popularity of Krav-Maga, its origins, history, and evolution have not been seriously examined in the academic literature, nor has its key role in promoting the use of reflex reactions in combat. This paper addresses these gaps in the literature while emphasizing the distinctive characteristics of Israeli combat disciplines. It also challenges popular misconceptions about the historical roots of Krav-Maga. Our research leads to three key conclusions: First, Israeli combat disciplines played a pioneering role in the use of situational awareness and reflex responses to an attack – in preference to a reliance on forms training. Second, contrary to commonly held beliefs, Krav-Maga is a direct development of Jewish hand-to-hand combat disciplines that can be traced back to 1891. Third, the development of Krav-Maga may be viewed as a reflection of historical and political events affecting the Jewish people from the late nineteenth century.     

A systematic analysis of performance measures for classification tasks

This paper presents a systematic analysis of twenty four performance measures used in the complete spectrum of Machine Learning classification tasks, i.e., binary, multi-class, multi-labelled, and hierarchical. For each classification task, the study relates a set of changes in a confusion matrix to specific characteristics of data. Then the analysis concentrates on the type of changes to a confusion matrix that do not change a measure, therefore, preserve a classifier’s evaluation (measure invariance). The result is the measure invariance taxonomy with respect to all relevant label distribution changes in a classification problem. This formal analysis is supported by examples of applications where invariance properties of measures lead to a more reliable evaluation of classifiers. Text classification supplements the discussion with several case studies.     

Effect of postural changes on 3D joint angular velocity during starting block phase

Abstract

Few studies have focused on the effect of posture during sprint start. The aim of this study was to measure the effect of the modification of horizontal distance between the blocks during sprint start on three dimensional (3D) joint angular velocity. Nine trained sprinters started using three different starting positions (bunched, medium and elongated). They were equipped with 63 passive reflective markers, and an opto-electronic Motion Analysis® system was used to collect the 3D marker trajectories. During the pushing phase on the blocks, norm of the joint angular velocity (NJAV), 3D Euler angular velocity (EAV) and pushing time on the blocks were calculated. The results demonstrated that the decrease of the block spacing induces an opposite effect on the angular velocity of joints of the lower and the upper limbs. The NJAV of the upper limbs is greater in the bunched start, whereas the NJAV of the lower limbs is smaller. The modifications of NJAV were due to a combination of the movement of the joints in the different degrees of freedom. The medium start seems to be the best compromise because it leads, in a short pushing time, to a combination of optimal joint velocities for upper and lower segments.     

Learning from Non-Reported Data: Interpreting Missing Body Mass Index Values in Young Children

The objective of this study was to examine the pattern of relations between missing weight and height (BMI) data and a range of demographic, physical activity, sedentary behavior, and academic measures in a young sample of elementary school children. A secondary analysis of a large cross-sectional study, PLAY-On, was conducted using self-reported data from a convenience sample of fifth- to eighth-grade students (9–14 years) attending 30 elementary schools in Ontario, Canada. Items assessed related to demographics (age, gender, and ethnicity), physical activity (energy expenditure, location, and sport participation), sedentary behavior (communication and screen-time), and academics. Of the 2,111 children who were included in the analyses, 960 (45.5%) were missing BMI data. Children without BMI data were more likely to be younger, female, of non-white ethnicity, have lower daily energy expenditure values, not participate in school sports, and have lower-rated academic standing than those children with BMI data. Overall, this study demonstrates characteristics of children who fail to self-report their height or weight. The trend for younger children to be more likely to fail to report BMI suggests that some children may be unmotivated non-responders. Meanwhile, the trend for girls to be more likely to fail to report weight than boys indicates that some girls may be motivated non-responders. Self-report BMI might include too much missing data to be effective for determining children's progress toward previously established targets for intervention and surveillance efforts.     

The inclusion of inclusive education in international development: Lessons from Papua New Guinea

A new ‘inclusive’ curriculum has been introduced in Papua New Guinea, with significant levels of support from a bilateral development agency. The curriculum is inclusive in the sense that it is designed to meet the diverse, complex, and ever-changing needs of students. Research indicates the curriculum has been shaped by various influences, most particularly Western educational ideology. Research in remote rural schools revealed that stakeholders were unable and unwilling to adopt many of the precepts of the new curriculum. Broader analysis indicates that this is likely to be the case elsewhere in PNG. In the light of these findings, it is proposed that international development agencies (IDAs), if they wish to effectively promote inclusive education, should become more ‘inclusive’ organisations – in the sense that they should adopt more responsive and participatory approaches in low income countries.