Muscle activation characteristics in cross-country skiers with a history of anterior compartment pain     

Peter Federolf  Emily Bakker 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(4):452-463

A large proportion of elite cross-country skiers suffer from chronic anterior compartment syndrome (CACS). This study used surface electromyograms (EMGs) to investigate whether differences existed in the activation characteristics of the tibialis anterior muscle between elite cross-country skiers with a history of anterior compartment pain (symptomatic group) and a pain-free control group. Based on self-reported pain symptoms, twelve young, national-level cross-country ski athletes were assigned to a symptomatic group (N = 5), a control group (N = 4), or analyzed individually if their diagnosis was not certain (N = 3). During skating, EMGs were recorded on five lower leg muscles. The relative increase in EMG power per step when increasing the effort level of skating was larger in the symptomatic group than in the control group for tibialis anterior (143 ± 12% vs. 125 ± 23%; Cohen's d = 1.17), peroneus longus (123 ± 24% vs. 107 ± 6%; d = 0.91), and gastrocnemius lateralis (167 ± 51% vs. 117 ± 12%; d = 1.64). The symptomatic group showed more power in the lower frequency bands of the tibialis anterior's EMG spectra (p < 0.001), whereas no group differences were found in other muscles (all p>0.2). Within the step cycle, these differences appeared in the swing phase and in the gliding phase during single leg support. The observed differences in the EMG spectra may serve as an early identification of athletes who are at risk of developing CACS.  相似文献   

Dominance in the prototyping phase—The case of hydrogen passenger cars     

Sjoerd Bakker  Harro van LenteMarius T.H. Meeus 《Research Policy》2012,41(5):871-883

The notion of dominant designs refers to dominance in the market, hence the literature on dominant designs ignores the selection process that already takes place in pre-market R&D stages of technological innovation. In this paper we address the question to what extent pre-market selection takes place within an industry and how this may lead to dominance of one design over others before the market comes into play. Furthermore we study what selection criteria apply in the absence of actual market criteria. We do so through a historical analysis of design paths for hydrogen passenger cars.We argue that prototypes are used by firms in their internal search process towards new designs and at the same time as means of communicating technological expectations to competitors and outsiders. In both senses, prototypes can be taken as indicators of design paths in the ongoing search process of an industry.We analyzed the designs of prototypes of hydrogen passenger cars from the 1970s till 2008. A database is compiled of 224 prototypes of hydrogen passenger cars, listing the car's manufacturer, year of construction, hydrogen conversion technology, fuel cell type, and capacity of its hydrogen storage system. The analysis shows to what extent one design gained dominance and which strategies were adopted by the firms in their search processes.We conclude that indeed a dominant prototyping design has emerged: the fuel cell combined with high pressure gaseous storage. Actual and expected performance acted as selection criterion, but so did regulation and strategic behaviour of the firms. Especially imitation dynamics, with industry leaders and followers, is a major explanatory factor. Our main theoretical claim is that the selection of a dominant prototyping design is based on an interaction of sets of expectations about future performance of technological components and regulatory pressure that results in herding behaviour of the firms.  相似文献   

Introduction of External,Independent Testing in “New Countries”: Successes and Defeats of the Introduction of Modern Educational Assessment Techniques in Former Soviet and Socialist Countries     

Steven Bakker 《Educational Measurement》2012,31(2):38-44

A particular trait of the educational system under socialist reign was accountability at the input side—appropriate facilities, centrally decided curriculum, approved text‐books, and uniformly trained teachers—but no control on the output. It was simply assumed that it met the agreed standards, which was, in turn, proven by the statistics provided by authorities. The introduction of professional testing methods for national large‐scale assessment efforts and participation in international surveys such as Trends in International Mathematics and Science Study (TIMSS) and Programme for International Student Assessment (PISA) unveiled the myth of the traditional “all is good” message spread by the former party rulers. But another aspect of the introduction of external independent testing has probably even had a bigger impact: the fight against the pervasive corruption in student admission it became part of. If any, the successful use of independent external testing in this struggle has done a lot to have its methods accepted by the audience at large. The article describes the experiences of the author as a senior consultant to ministries and newly established testing institutes in former Soviet and socialist republics.  相似文献   

Changes in the perception of action possibilities while climbing to fatigue on a climbing wall     

Pijpers JR  Oudejans RR  Bakker FC 《Journal of sports sciences》2007,25(1):97-110

In two experiments we examined changes in the perception of action possibilities as a function of exertion. In Experiment 1, participants repeatedly climbed on a climbing wall in a series of trials that progressively increased in number to 10 trials, resulting in increased exertion. Before and during climbing, the participants judged their maximum reaching height and perceived exertion. On a separate day, participants climbed another 10 trials while performing actual maximum reaches. Higher perceived exertion was associated with decreases in perceived maximum reach while the actual reaches did not decrease. However, the perceptual changes occurred early during task execution when the participants were not yet fatigued. When exertion set in, neither perceived nor actual maximum reaching appeared to be affected. In Experiment 2, we included exhaustion trials. The findings replicated the early changes in perception observed in Experiment 1, which may be explained by hands-on experience with the task. Furthermore, while climbing to exhaustion, perceptual judgements largely changed in keeping with changes in the actual maximum reach. Thus, there appeared to be a functional relationship between participants' actual action capabilities, rather than their state of physical fatigue per se, and perceived action possibilities.  相似文献   

To mediate or not: it depends on the medium     

Suzanne Bakker 《Health information and libraries journal》2000,17(1):41-45

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“…the bold atmosphere of Mrs. Hentz” and Others: Fast Food and Feminine Rebelliousness in Some Romances of the Old South     

Jan Bakker 《Journal of American culture (Malden, Mass. : 2003)》1998,21(2):1-6

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Neoliberal Education Reform in The Netherlands     

Sjoerd Karsten 《比较教育学》1999,35(3):303-317

Until recently the Dutch education system was determined by the historic compromise of 1917, after which private schools were supported by the state on an equal financial footing to state schools. The consequence of this compromise was a mainly privatised and centralised system with a corporatist policy structure. In the mid-1980s The Netherlands, like other countries, came under the spell of the 'neoliberal revolution'. This article explores the extent to which the management reform carried out under a neoliberal flag has brought about radical changes to the Dutch education system. It especially looks at four key issues set out in that reform: increased autonomy, freedom of choice, privatization and quality control.  相似文献   

Hemispheric specialization and stages in the learning-to-read process   总被引：2，自引：2，他引：0  

Dirk J. Bakker 《Annals of dyslexia》1973,23(1):15-27

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East Meets West in Assessment Development: Western Technical Assistance to Eastern Needs. Part II: Project and Team Management in the AERo Project in Romania     

Steven Bakker  Gerben van  Lent  Annemarie de Knecht-van Eekelen 《Educational Measurement》2001,20(2):36-39

This is Part II of a three-part series describing the consultancy and training demands that are encountered in technical assistance projects in Central and Eastern Europe. This part highlights project management and cooperation aspects in delivering support to the Romanian Assessment and Examination Service. Part I dealt with strategic issues for a successful delivery of "Western Technical Assistance to Eastern Needs." Part III will address training of Polish subject experts, preparing to take on responsibility for a decentralized and drastically changed final exam, the Matura.  相似文献   

Retroactive interference effects of mentally imagined movement speed     

Boschker MS  Bakker FC  Rietberg MB 《Journal of sports sciences》2000,18(8):593-603

In two retroactive interference experiments, we assessed the effect of mentally imagined movement speed on subsequent motor performance. All participants performed a sequential motor action at three speeds during a baseline test and a retention test. During the retention interval of Experiment 1, the participants (n = 50) physically performed the action at a slow speed, physically performed it at a fast speed, imagined it at a slow speed, imagined it at a fast speed, or performed a no-practice control task. In Experiment 2, the participants (n = 24) imagined the movement, overtly vocalized words, or both, all at a slow speed. The results revealed that the speed of the imagined motor action affected the speed of subsequent performance in the retention test and that imagery and physical practice were functionally equivalent. The results are consistent with Lang's bio-informational theory.  相似文献