1,720,992 research outputs found
Kinematics of sprint cross-country skiing.
No full textThe purpose of our study was to characterise the diagonal stride locomotion during a new short sprint race in cross-country skiing. Thirty male cross-country skiers were sagittaly filmed on an uphill portion of the 1.2-km classic race of the world cup (2004) using a digital camera. The main body joints, skis and poles were digitised frame by frame. Results indicated higher SV and SR for similar SL compared to longer distance races with a similar slope. Moreover, significant correlations were observed between SV and SR but not between SV and SL contrary to the other distance races. SL results showed that in spite of the high SR, skiers maintained an effective leg and pole thrusts. The high SR in KO sprint presented a mechanical advantage by minimising the decrease of velocity during the cycle. The importance of SR in the velocity production could be useful for practitioners to optimise the training program for this type of race. It seemed notable that the skiers had to improve temporal factors while conserving a long SL
Effect of fatigue on double pole kinematics in sprint cross-country skiing.
No full textThe aim of the present study was to examine the effect of fatigue (physiological, mechanical, and muscular parameters) induced by a sprint simulation on kinematic parameters (cycle, phases, and joints angles) of the double pole technique. Eight elite skiers were tested for knee extensor strength and upper body power both before and after a three-bout simulation of sprint racing. They were video analyzed during the final part of the test track of bouts 1 and 3 using a digital camera. Results showed that skiers were in a fatigue state (decrease of the knee extensors voluntary force (-10.4+/-10.4%) and upper body power output (-11.1+/-8.7%) at the end of the sprint. During bout 3, the final spurt and cycle velocities decreased significantly (-7.5+/-12.3%; -13.2+/-9.5%; both p<.05). Angular patterns were only slightly modified between bouts 1 and 3 with trunk, hip, and pole angles being significantly greater for the third bout. The decrease of hip and trunk flexion and the lower inclination of the pole during the poling phase suggested a reduced effectiveness of the force application which could lead to a decrease in the cycle velocity
Velocity, rate and length relationship during cross country skiing KO sprint
No full textThe purpose of our study was to characterise the kinematic of the diagonal stride during a
new short sprint race in cross country skiing. We hypothesised that the locomotion in KO
sprint was characterised by a high cycle rate (FC) and a low cycle length (AC). Thirty male
cross-country skiers were filmed on an uphill portion (5% sur 200 m) of the 1.2-Km classic
race of the world cup. Cycle velocities (VC) obtained were of de 4,77 ± 0,56 m.s-1, with cycle
rate (FC) and cycle length (AC) respectively of 2,19 ± 0,27 Hz et 2,15 ± 0,19 m. Significant
correlations were observed between VC and FC but not between VC and AC. The high frequencies
observed during the KO sprint appeared to be a mechanical advantage by minimising
the lost of velocity during the non propulsive phases
Muscle fatigue during cross country sprint assessed by activationpatterns and electromyographic signals time-frequency analysis
No full textThe aims of this study were as follows: (i) analysis of activation patterns during the spurt of two heats of a cross country skiing sprint with the double poling technique and (ii) quantification of muscle fatigue of the investigated muscles. Eight elite skiers were tested and surface electromyographic signals (EMG) were recorded from seven muscles of the upper and lower limbs. For each subject and each muscle, the activation intervals were calculated for relying on a double-threshold statistical detector and the average rectified value was calculated on each activation interval. The detected activations were processed by a time-frequency algorithm in order to assess the progression of muscle fatigue. The EMG activation patterns and EMG amplitude highlighted no significant difference between the two spurts, despite a generally lower speed in the second spurt. The frequency analysis showed that upper body muscles are the first to be affected by fatigue and that clear signs of muscle fatigue appear right from the first spurt of the sprint simulation (i.e., biceps and triceps brachii) with a decrease in the instantaneous mean frequency. Biceps brachii activations and fatigue demonstrated the involvement of this muscle in propulsion
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Neuromuscular adaptations to electrostimulation resistance training
No full textA combination of in vivo and in vitro analyses was performed to investigate muscular and neural adaptations of the weaker (nondominant) quadriceps femoris muscle of one healthy individual to short-term electrostimulation resistance training. The increase in maximal voluntary strength (+12%) was accompanied by neural (cross-education effect and increased muscle activation) and muscle adaptations (impairment of whole-muscle contractile properties). Significant changes in myosin heavy chain (MHC) isoforms relative content (+22% for MHC-2A and -28% for MHC-2X), single-fiber cross-sectional area (+27% for type 1 and +6% for type 2A muscle fibers), and specific tension of type 1 (+67%) but not type 2A fibers were also observed after training. Plastic changes in neural control confirm the possible involvement of both spinal and supraspinal structures to electrically evoked contractions. Changes at the single muscle fiber level induced by electrostimulation resistance training were significant and preferentially affected slow, type 1 fiber
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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