The aim of this study was to examine the effects of muscle-tendon length on joint moment and power during maximal sprint starts. Nine male sprinters performed maximal sprint starts from the blocks that were adjusted either to 40 degrees or 65 degrees to the horizontal. Ground reaction forces were recorded at 833 Hz using a force platform and kinematic data were recorded at 200 Hz with a film camera. Joint moments and powers were analysed using kinematic and kinetic data. Muscle - tendon lengths of the medial gastrocnemius, soleus, vastus medialis, rectus femoris and biceps femoris were calculated from the set position to the end of the first single leg contact. The results indicated that block velocity (the horizontal velocity of centre of mass at the end of the block phase) was greater (P < 0.01) in the 40 degrees than in the 65 degrees block angle condition (3.39 +/- 0.23 vs. 3.30 +/- 0.21 m . s(-1)). Similarly, the initial lengths of the gastrocnemius and soleus of the front leg in the block at the beginning of force production until half way through the block phase were longer (P < 0.001) in the 40 degrees than in the 65 degrees block angle condition. The initial length and the length in the middle of the block phase were also longer in the 40 degrees than in the 65 degrees block angle condition both for both the gastrocnemius (P < 0.01) and soleus (P < 0.01-0.05) of the rear leg. In contrast, the initial lengths of the rectus femoris and vastus medialis of the front leg were longer (P < 0.05) in the 65 degrees than in the 40 degrees block angle condition. All differences gradually disappeared during the later block phase. The peak ankle joint moment (P < 0.01) and power (P < 0.05) during the block phase were greater in the 40 degrees than in the 65 degrees block angle condition for the rear leg. The peak ankle joint moment during the block phase was greater (P < 0.05) in the 40 degrees block angle for the front leg, whereas the peak knee joint moment of the rear leg was greater (P < 0.01) in the 65 degrees block angle condition. The results suggest that the longer initial muscle-tendon lengths of the gastrocnemius and soleus in the block phase at the beginning of force production contribute to the greater peak ankle joint moment and power and consequently the greater block velocity during the sprint start. 相似文献
This paper presents a newly developed digital redesign control scheme with a weighted switching strategy and output-reference tracking, for a cascaded analog system with state saturation and external loads. The proposed method improves the generally poor transition response and output deviation caused by state-saturation constraint and external loads. It replaces an existing or theoretically well-designed analog controller with state saturation, by a digital controller with almost identical performance. 相似文献
Adopting a longitudinal approach, this article examines downward occupational mobility (DOM) later in working life and its effects on job satisfaction and perceptions of working conditions of older workers in Europe. The main aim was to test whether the risk that workers will be negatively impacted and marginalized in the labor market due to demotion into lower quality jobs is offset by benefits. Based on an ordinal logistic regression of merged Survey of Health, Ageing and Retirement in Europe and English Longitudinal Study of Ageing datasets, the study found a positive significant impact of DOM on overall job satisfaction. Moreover, DOM was associated with a statistically significant reduction in workload pressure, although it did increase physical work demand. This article adds to the literature on marginalization of workers with indications that the lower income and status associated with DOM at older ages may have offsetting benefits. 相似文献
This paper explores the experiences of a group of academic developers who support educational development work as Faculty Liaisons at a large, research-intensive university. These academic developers inhabit complex ‘third spaces’, providing support through an embedded partnership relationship that requires lateral movement across functional and organizational boundaries to create new professional spaces, knowledge, and relationships. The authors utilize narrative inquiry and auto-ethnographic approaches to present an interpretive qualitative analysis of their experiences supporting Faculty and University projects across complex and evolving organizational boundaries. From this analysis, they highlight key roles and responsibilities associated with their blended context and identify challenges that academic developers who occupy third spaces within academic organizations face as they negotiate competing interests, identities, and requirements associated with the diverse range of their projects and the blended experience of working in scholarly and administrative, central- and Faculty-based roles. The lessons they have learned from these experiences will be of particular interest to academic developers who are experiencing the flux of change within higher education settings that are impacting teaching and learning practices both for faculty in the classroom and for those across the institution who support them. 相似文献
Abstract The recent introduction of micro‐computers into schools is opening up many new avenues for developmental psychologists interested in studying how children learn. Of particular interest at present are approaches in which children program computers themselves, using languages such as LOGO and PROLOG. This paper describes a study in which a simplified version of LOGO was introduced to a group of six‐year‐olds in a severely deprived area of Edinburgh. The children used a special touch‐sensitive keyboard (Concept Keyboard) to control the movements of a floor‐crawling robot called a Turtle. The sessions with the Turtle were marked by high levels of concentration, collaborative problem‐solving and the use of mathematical language. Pre‐ and post‐tests on the British Ability Scales revealed statistically significant gains on the sub‐scales concerned with number and shape: these gains, however, were found only in the boys.相似文献
Increases in the number of college students seeking mental health services require counseling centers to explore innovative strategies to provide effective and efficient treatments. Group interventions offer an alternative to traditional individual counseling, allowing centers to serve more students with fewer clinical staff (Burlingame et al., 2016). Of current group modalities, mindfulness-based interventions (MBIs) have been growing in popularity as an effective approach for addressing college students’ increasingly complex needs. This study describes the evaluation of a three-session mindfulness-based intervention on students’ mindfulness, symptoms, and stress. Compared to a comparison group of 109 students not seeking counseling center services, 78 students who received the intervention reported increased mindfulness, and decreased symptoms of depression, anxiety, and stress at the end of the group. Furthermore, improvements in mindfulness mediated intervention effects on symptoms of depression and anxiety. These gains were generally maintained 3 weeks later. These findings support the benefits of brief group interventions for college students. Suggestions for modifications to the intervention and for future research are discussed. 相似文献
In this contribution, a theoretical and empirical framework based on work carried out at the Open universiteit (Ou) for a new approach towards the design, production and delivery of flexible, interactive learning materials for distance education is presented.
In the Research and Development centre of the Ou, a project has concentrated on the innovation of current approaches. This framework can also be considered as an advance organizer to reading the remaining articles from the Open universiteit in this issue of Distance Education.
A key feature of the innovation is that during the design phase, course developers have to define ‘models’ of the materials to be developed: a content model, a support model, a student model and the learning path. From a flexibility point of view especially, the ‘student model’ is of importance since it defines the student variables that will be taken into account when developing/ presenting alternative materials (basic content and/or embedded support). A computer‐based system, the ‘Interactive Learning and Course Development Environment (ILCE)’, was developed to support the work of course development teams and tutors on the one hand, and students on the other hand. The development system supports the work of the developers; the delivery system supports the study process of students. The delivery is realised as an on‐line course, on the World Wide Web.
Students start working with the ILCE‐system by following an intake procedure. They can make choices in relation to student variables that have been defined in the student model (profession, study intentions, context, etc.). Next, they can ‘on the fly’ generate a course. Rom the large repository of learning materials only those materials are selected and compiled that are in line with the student model of this specific student Furthermore, they can choose to study the materials on screen and/or make prints of the materials. Of course, in printing the materials they lose the interactive and dynamic possibilities of the computer learning environment 相似文献