Effect of ski boot rear stiffness (SBRS) on maximal ACL force during injury prone landing movements in alpine ski racing: A study with a musculoskeletal simulation model

A common anterior cruciate ligament (ACL) injury situation in alpine ski racing is landing back-weighted after a jump. Simulated back-weighted landing situations showed higher ACL-injury risk for increasing ski boot rear stiffness (SBRS) without considering muscles. It is well known that muscle forces affect ACL tensile forces during landing. The purpose of this study is to investigate the effect of different SBRS on the maximal ACL tensile forces during injury prone landings considering muscle forces by a two-dimensional musculoskeletal simulation model. Injury prone situations for ACL-injuries were generated by the musculoskeletal simulation model using measured kinematics of a non-injury situation and the method of Monte Carlo simulation. Subsequently, the SBRS was varied for injury prone landings. The maximal ACL tensile forces and contributing factors to the ACL forces were compared for the different SBRS. In the injury prone landings the maximal ACL tensile forces increased with increasing SBRS. It was found that the higher maximal ACL force was caused by higher forces acting on the tibia by the boot and by higher quadriceps muscle forces both due to the higher SBRS. Practical experience suggested that the reduction of SBRS is not accepted by ski racers due to performance reasons. Thus, preventive measures may concentrate on the reduction of the quadriceps muscle force during impact.     

Wandel der Schulkultur

Zusammenfassung Der Beitrag diskutiert die Entwicklung der Schulkultur in den letzten Jahrzehnten. Die Schulkultur, als eine sich universalisierende kulturelle Form, wird von der Pluralit?t l?nderspezifischer, regionaler und lokaler „Schulkulturen“ unterschieden. Diese Schulkulturen werden begriffen als symbolische, sinnstrukturierte Ordnungen der einzelnen Schulen, die von den schulischen Akteuren in der Auseinandersetzung mit ?u?eren Strukturvorgaben konkret ausgestaltet werden. Für vier Dimensionen der Schulkultur werden thesenhaft Entwicklungsrichtungen formuliert: Für die schulischen Anerkennungs- und Partizipationsverh?ltnisse wird die Abl?sung des besonderen Gewaltverh?ltnisses durch eine ambivalente Partizipationsaufforderung behauptet. Für die Leistungsdimension wird deren zunehmende Vorrangstellung und die Universalisierung individualisierter Leistungserbringung diagnostiziert. Für die p?dagogischen Orientierungen wird die Entwicklung von einer Unterordnungs- und Gehorsamsforderung hin zur antinomischen Anforderung an informalisierte schulische Aushandlungsprozesse festgestellt und für die Fachinhalte die These einer Entwicklung des Kanons zum flexibilisierten Angebot und seinen Ambivalenzen aufgestellt. Abschlie?end werden grundlegende Bestimmungen zum Verh?ltnis von System. Organisation, Reflexion und Profession für die Schule heraus gearbeitet. Die Schulkultur wird als Kultur einer inkonsistenten. nicht zum Abschlu? gelangten Systembildung des P?dagogischen verstanden mit daraus resultierenden Strukturproblemen. die in jeder Schule eine eigene Bearbeitung und Ausdruckgestalt erf?hrt.

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Summary A changing school culture This paper discusses the developments in school culture during the last few decades. School culture, as a universalising cultural form, is understood as distinct from the plurality of country specific, regional, and local ‘school cultures’. These school cultures are understood as symbolic, meaning-structuring constellations present in individual schools, which are finally shaped by their actors in interaction with their respective structural environment. Development trajectories will be sketched for four dimensions of school culture: For the dimensions of recognition and participation in the school environment, a substitution of traditional power relations for the ambivalent demands of increased participation is claimed. Concerning the performance dimension, its increasing importance per se and the universalisation of individualised performance is diagnosed. For the pedagogical orientation, a development away from demands of subservience and obedience towards the antonymous demand for an informal negotiation process within the school setting is determined and, regarding school subjects, a development of the curriculum towards a more flexible offer, and the ambivalence of this, is proposed and discussed. Finally, fundamental determinants of the relationship between system, organisation, reflection and profession are constructed for the school. School culture is understood as an inconsistent systemic development, which has not yet reached completion. This results in structural problems, which every school processes and articulates in its own way.

     

Is it possible to voluntarily increase hamstring muscle activation during landing from a snow jump in alpine skiing? - a pilot study

Activation of the hamstrings has been discussed as a measure for reducing strain on the ACL during jump landings in alpine skiing. The current study tested the hypothesis that hamstring and quadriceps activation can be voluntarily increased by the athlete. Specifically, two different instructions – to increase hamstring activation or to increase upper-leg co-contraction – were compared to normal landings. Eight members of the German national and junior national squad in freestyle skiing (age 19.6 ± 3.8 years; weight 66.1 ± 13.2 kg; height 172.2 ± 7.7 cm) performed 12 jump landings on a prepared run, 4 with no specific instruction, 4 with the instruction to generally activate the thigh muscles, and 4 with the instruction to specifically activate the hamstrings. Electromyographic (EMG) signals were recorded on the biceps femoris (BF), semitendinosus (ST), vastus lateralis (VL), rectus femoris (RF) and vastus medialis (VM). EMG activation levels were integrated over three landing phases and analysed with a repeated measures ANOVA. The instruction produced a significant main effect in ST (p = .026), VM (p = .032) and RF (p = .001). Contrary to previous research, the current study suggests that hamstring muscle activation levels can be voluntarily increased during jump landing, particularly in co-activation with its antagonists.     

Age-specific response of skeletal muscle extracellular matrix to acute resistance exercise: A pilot study

The extracellular matrix (ECM) plays an essential role in the development, growth and repair of skeletal muscles and serves to transmit contractile force. However, its regulation is poorly understood. This study investigates the age-specificity of the effects of acute resistance exercise on ECM gene expression. To this purpose, five young (YM, 23.8?±?2.2 yrs.) and 5 elderly (EM, 66.8?±?4.1 yrs.) men performed one session of unilateral leg press and leg extension exercises. Six hours post-exercise, biopsies were taken from the vastus lateralis muscles of both legs. A PCR array was used to profile the expression of 84 ECM-related genes, of which 6 were validated by qPCR. The PCR array found 9 and 4 ECM-associated genes to be selectively altered (>1.5-fold change) in YM or EM only. Four further genes were upregulated in YM but downregulated in EM. Of the 6 genes validated on individual samples MMP9 expression increased in YM (9.7-fold) and decreased (0.2-fold) in EM. MMP15 was downregulated in EM only (0.6-fold). A significant correlation between leg extension 1 RM and changes in COL7A1 expression (ρ?=?0.71) suggests a potential influence of fitness levels. In conclusion, acute resistance exercise affects ECM gene expression at least partly in an age-specific manner. The altered expression of genes encoding matrix metalloproteinases (MMP3, MMP9, MMP15) highlights the role of remodelling processes in the response to an acute bout of resistance exercise. Larger studies are required to verify the age-associated differences in gene expression profiles and establish their functional implications.     

Helsen, Gilis, and Weston (2006) do not err in questioning the optical error hypothesis as the only major account for explaining offside decision-making errors

Oudejans, Bakker, and Beek (2007) recognize several relevant aspects of offside judgements in association football in the paper by Helsen, Gilis, and Weston (2006). We agree that the existing knowledge base on offside assessment needs to be expanded for two reasons. First, from a theoretical point of view it is important to examine how assistant referees can learn to deal with the limitations of the human visual information processing system. Second, from a practical point of view it is relevant to understand better refereeing performances and to identify potential explanations for incorrect offside decisions that could impact on the final outcome of the game. Oudejans et al. (2007) believe we both misinterpreted the optical error hypothesis and that our data set was unsuited to test it. Below, we react to these comments.     

Measuring spontaneous and instructed evaluation processes during Web search: Integrating concurrent thinking-aloud protocols and eye-tracking data

Web searching for complex information requires to appropriately evaluating diverse sources of information. Information science studies identified different criteria applied by searchers to evaluate Web information. However, the explicit evaluation instructions used in these studies might have resulted in a distortion of spontaneous evaluation processes. Accordingly, the present study compared explicit evaluation instructions and neutral thinking-aloud instructions. Data from thinking-aloud protocols, eye tracking, and information problem-solving were collected from 30 participants equally distributed to two experimental conditions, that is, the Instructed Evaluation condition and the Spontaneous Evaluation condition. Instructed evaluation, as compared to spontaneous evaluation, resulted in more verbal utterances of quality-related evaluation criteria, in an increased attention focus on user ratings displayed on Web pages, and in better quality of decision making, although participants in the Instructed Evaluation condition were not able to better justify their decision as compared to participants in the Spontaneous Evaluation condition.     

Influence of source credibility on students’ noticing and assessing comprehension obstacles in science texts

This study aims to analyse the effect of source credibility on students’ identification and assessment of comprehension obstacles in science texts. Source credibility was manipulated by providing 12th grade students with paragraphs supposedly taken from science textbooks or, alternatively, from students’ reports. The paragraphs contained information expected to be difficult to understand by the participating students. The students were instructed to report any comprehension obstacle they might find and to rate the comprehensibility of the paragraphs. There was no effect of source credibility on noticing and reporting comprehension obstacles in the conditions of our experiments. However, there was a significant finding regarding comprehensibility scores. The students rated the comprehensibility of the paragraphs supposedly taken from science textbooks higher than the comprehensibility of the same paragraphs supposedly taken from peer reports. The finding has implications on the way students approach the understanding of science texts. An enhancement of students’ feelings of competence in dealing with scientific subject matter would have a beneficial effect on students’ assessment and validation of information in science texts.     

Applied mathematical problem solving,modelling, applications,and links to other subjects — State,trends and issues in mathematics instruction

The paper will consist of three parts. In part I we shall present some background considerations which are necessary as a basis for what follows. We shall try to clarify some basic concepts and notions, and we shall collect the most important arguments (and related goals) in favour of problem solving, modelling and applications to other subjects in mathematics instruction. In the main part II we shall review the present state, recent trends, and prospective lines of development, both in empirical or theoretical research and in the practice of mathematics instruction and mathematics education, concerning (applied) problem solving, modelling, applications and relations to other subjects. In particular, we shall identify and discuss four major trends: a widened spectrum of arguments, an increased globality, an increased unification, and an extended use of computers. In the final part III we shall comment upon some important issues and problems related to our topic.Written version of a Survey Lecture given jointly at the Sixth International Congress on Mathematical Education (ICME-6, Budapest 1988). A condensation was published in a volume with contributions from the ICME-6 Theme Groups on Problem Solving, Modelling and Applications and on Mathematics and Other Subjects (Blum/Niss/Huntley 1989, pp. 1–21).     

Reading training by means of disappearing text: effects on reading performance and eye movements

The Reading Acceleration Program (RAP), which uses adaptively increasing text erasure rates to enforce reading rate improvements, has been positively evaluated in various languages, reader and age groups. The current study compared the established incremental increase of text erasure rate with a training using fixed erasure rates in two groups of young, non-impaired German adults. Eye-tracking measures prior and post training examined training-related changes of eye-movement patterns. Equal gains in reading performance in both training groups led to the conclusion that not the adaptive increase but already text erasure at fixed rates provides an economically efficient tool for the enhancement of reading rates. Furthermore, eye-tracking results suggest that text erasure training affects word processing not only at one specific level, but simultaneously at pre-lexical, lexical, and post-lexical stages. Although these outcomes are promising, further research is necessary to determine the optimal individual erasure rates that preserve good comprehension at varying levels of text difficulty and in different orthographies.