Force-velocity characteristics of upper limb extension during maximal wheelchair sprinting performed by healthy able-bodied females     

Hintzy F  Tordi N  Predine E  Rouillon JD  Belli A 《Journal of sports sciences》2003,21(11):921-926

The aim of this study was to determine the relationship between force and velocity parameters during a specific multi-articular upper limb movement--namely, hand rim propulsion on a wheelchair ergometer. Seventeen healthy able-bodied females performed nine maximal sprints of 8 s duration with friction torques varying from 0 to 4 N x m. The wheelchair ergometer system allows measurement of forces exerted on the wheels and linear velocity of the wheel at 100 Hz. These data were averaged for the duration of each arm cycle. Peak force and the corresponding maximal velocity were determined during three consecutive arm cycles for each sprint condition. Individual force-velocity relationships were established for peak force and velocity using data for the nine sprints. In line with the results of previous studies on leg cycling or arm cranking, the force-velocity relationship was linear in all participants (r = -0.798 to -0.983, P < 0.01). The maximal power output (mean 1.28 W x kg(-1)) and the corresponding optimal velocity (1.49 m x s(-1)) and optimal force (52.3 N) calculated from the individual force-velocity regression were comparable with values reported in the literature during 20 or 30 s wheelchair sprints, but lower than those obtained during maximal arm cranking. A positive linear relationship (r = 0.678, P < 0.01) was found between maximal power and optimal velocity. Our findings suggest that although absolute values of force, velocity and power depend on the type of movement, the force-velocity relationship obtained in multi-articular limb action is similar to that obtained in wheelchair locomotion, cycling and arm cranking.  相似文献   

Reviews     

Alan Chalmers  Lloyd Ackert  Pnina Abir-Am  Maria Trochatos  Carolyn R. Miller  Nicolas Rasmussen  Roy Macleod  Ingo Brigandt  Lorna Barrow  Ian Maclean  Elof Axel Carlson  Susan E. Cozzens  Cindy Klestinec  Patricia O'Grady  Alison Bashford  Jim Endersby  Jonathan Simon  David Mercer  David Oldroyd  Suzanne Verderber  Peter Slezak  Rachel Cooper  Patricia Fara  Ravi Arvind Palat  Peder Anker  Bernhard Fritscher  David Branagan 《Metascience》2002,11(3):329-429

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Learning-based summarisation of XML documents     

Massih R. Amini  Anastasios Tombros  Nicolas Usunier  Mounia Lalmas 《Information Retrieval》2007,10(3):233-255

Documents formatted in eXtensible Markup Language (XML) are available in collections of various document types. In this paper, we present an approach for the summarisation of XML documents. The novelty of this approach lies in that it is based on features not only from the content of documents, but also from their logical structure. We follow a machine learning, sentence extraction-based summarisation technique. To find which features are more effective for producing summaries, this approach views sentence extraction as an ordering task. We evaluated our summarisation model using the INEX and SUMMAC datasets. The results demonstrate that the inclusion of features from the logical structure of documents increases the effectiveness of the summariser, and that the learnable system is also effective and well-suited to the task of summarisation in the context of XML documents. Our approach is generic, and is therefore applicable, apart from entire documents, to elements of varying granularity within the XML tree. We view these results as a step towards the intelligent summarisation of XML documents.

Mounia LalmasEmail:

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A Distribution Free Interval Estimate for Coefficient Alpha     

Laura Trinchera  Nicolas Marie  George A. Marcoulides 《Structural equation modeling》2018,25(6):876-887

Scales are important tools for obtaining quantitative measures of theoretical constructs. Once a set of measures to be used in a scale is selected, reliability is commonly examined in order to assess their measurement quality. To date, Cronbach’s coefficient alpha is the most commonly reported index of measurement quality for assessing scale reliability. In this paper, an asymptotic distribution of the natural estimator of coefficient alpha is derived. A new interval estimate and a statistical test on the significance of the sample estimate of the coefficient are also presented. The proposed approach is compared to four popular methods commonly used to compute confidence intervals (CI) for alpha using a Monte Carlo simulation study. An R function for implementing the proposed CI approach is also provided.  相似文献   

Willing to Think Hard? The Subjective Value of Cognitive Effort in Children          下载免费PDF全文

Nicolas Chevalier 《Child development》2018,89(4):1283-1295

Cognitive effort is costly and this cost likely influences the activities in which children engage. Yet, little is known about how school‐age children perceive cognitive effort. The subjective value of cognitive effort, that is, how valuable or costly effort is perceived, was investigated in seventy‐three 7‐ to 12‐year‐olds using an effort discounting paradigm. In two studies, it varied with task difficulty but not age, was predicted by actual effort engagement but not actual success and related to trait interest in effortful activities and proactive control engagement. Children are sensitive to cognitive effort and use it to guide behaviors, suggesting that poor performance may often reflect reluctance to engage cognitive effort rather than low ability.  相似文献   

Performance determinants of fixed gear cycling during criteriums     

Nicolas Babault  Maxime Poisson  Guiseppe Cimadoro  Carole Cometti  Christos Païzis 《European Journal of Sport Science》2018,18(9):1199-1207

Nowadays, fixed gear competitions on outdoor circuits such as criteriums are regularly organized worldwide. To date, no study has investigated this alternative form of cycling. The purpose of the present study was to examine fixed gear performance indexes and to characterize physiological determinants of fixed gear cyclists. This study was carried out in two parts. Part 1 (n?=?36) examined correlations between performance indexes obtained during a real fixed gear criterium (time trial, fastest laps, averaged lap time during races, fatigue indexes) and during a sprint track time trial. Part 2 (n?=?9) examined correlations between the recorded performance indexes and some aerobic and anaerobic performance outputs (VO_2max, maximal aerobic power, knee extensor and knee flexor maximal voluntary torque, vertical jump height and performance during a modified Wingate test). Results from Part 1 indicated significant correlations between fixed gear final performance (i.e. average lap time during the finals) and single lap time (time trial, fastest lap during races and sprint track time trial). In addition, results from Part 2 revealed significant correlations between fixed gear performance and aerobic indicators (VO_2max and maximal aerobic power). However, no significant relationship was obtained between fixed gear cycling and anaerobic qualities such as strength. Similarly to traditional cycling disciplines, we concluded that fixed gear cycling is mainly limited by aerobic capacity, particularly criteriums final performance. However, specific skills including technical competency should be considered.  相似文献