KINEMATIC SYMMETRY IN ROWING: COMPARISON OF FIXED STRETCHER VERSUS FREE-FLOATING ERGOMETER

The purpose of this study was to examine kinematic symmetry of lower and upper limbs when using two kinds of rowing ergometers. Fifteen high-level rowers performed two 15stroke tests at a race rate on two different Rowperfect rowing ergometers. One was fitted up with a fixed stretcher mechanism and the other with a free-floating stretcher mechanism. The tests were carried out in a randomised order. Flexion/extension angles were computed from trajectories of twenty-two markers collected by a motion analysis system. A functional data framework was realised to compare right versus left side angle function curves. These angle curves were validated by bibliographic data. High levels of symmetry were observed for angles of the lower and upper limbs regardless of the mechanism rowed. Shoulder and hip angles for the fixed and the free-floating conditions respectively, were the only exceptions in this regard. The rower's symmetry pointed out by this work allows one-side kinematical analysis of flexion/extension angles

The Alestle - Vol. 58 No. 52 - 04/11/2006

Vol. 58 No. 5

Emotions and performance in rugby

Purpose: This study investigated emotion-performance relationships in rugby union. We identified which emotions rugby players experienced and the extent to which these emotions were associated with performance, considering how emotions unfold over the course of a game, and whether the game was played at home or away. Methods: Data were gathered from 22 professional male rugby union players using auto-confrontation interviews to help identify situations within games when players experienced intense emotions. We assessed the intensity of emotions experienced before each discrete performance and therefore could assess emotion-performance relationships within competition. Results: Players identified experiencing intense emotions at 189 time-points. Experts in rugby union rated the quality of each performance at these 189 time-points on a visual analog scale. A Linear Mixed Effects model to investigate emotion-performance relationships found additive effects of game location, game time, and emotions on individual performance. Conclusion: Results showed 7 different pre-performance emotions, with high anxiety and anger associating with poor performance. Future research should continue to investigate emotion-performance relationships during performance using video-assisted recall and use a measure of performance that has face validity for players and coaches alike

Effects of Age and Task Load on Drivers’ Response Accuracy and Reaction Time When Responding to Traffic Lights

International audienceDue to population aging, elderly drivers represent an increasing proportion of car drivers. Yet, how aging alters sensorimotor functions and impacts driving safety remains poorly understood. This paper aimed at assessing to which extent elderly drivers are sensitive to various task loads and how this affects the reaction time (RT) in a driving context. Old and middle-aged people completed RT tasks which reproduced cognitive demands encountered while driving. Participants had to detect and respond to traffic lights or traffic light arrows as quickly as possible, under three experimental conditions of incremental difficulty. In both groups, we hypothesized that decision-making would be impacted by the number of cues to be processed. The first test was a simple measure of RT. The second and third tests were choice RT tasks requiring the processing of 3 and 5 cues, respectively. Responses were collected within a 2 s time-window. Otherwise, the trial was considered a no-response. In both groups, the data revealed that RT, error rate (incorrect answers), and no-response rate increased along with task difficulty. However, the middle-aged group outperformed the elderly group. The RT difference between the two groups increased drastically along with task difficulty. In the third test, the rate of no-response suggested that elderly drivers needed more than 2 s to process complex information and respond accurately. Both prolonged RT and increased no-response rate, especially for difficult tasks, might attest an impairment of cognitive abilities in relation to aging. Accordingly, casual driving conditions for young drivers may be particularly complex and stressful for elderly people who should thus be informed about the effects of normal aging upon driving

Likelihood Ratio Tests

International audienceThe LRT is a principal method in a standard hypothesis testing framework. It parallels the maximum likelihood method in estimation theory

Relative Age Effect and chi-squared statistics

International audienc

Que signifie la significativité statistique ? L'apport de la taille d'effet et de la puissance statistique

International audienceTrotz ihrer Sachdienlichkeit und ihrer Bedeutung werden die statistischen Größen der Teststärke und der Effektgröße in der Sportwissenschaft bisher nur sehr wenig benutzt. Anhand zweier unterschiedlicher Untersuchungen illustriert der vorliegende Aufsatz die zahlreichen Vorteile ihrer Verwendung. Der Rückgriff auf diese beiden Größen könnte einerseits den Beitrag von einigen Studien ans Licht bringen, die an einer mangelnden Signifikanz kranken (oft bedingt durch kleine Stichproben, was beim ersten Beispiel der Fall ist), und für die es schwer ist, trotz ihrer tatsächlichen Bedeutung, die daraus resultierenden „Konklusionen“ zu verteidigen. Besonders die Bestimmung der Effektgröße hebt die konkrete Bedeutung der gemessenen Effekte hervor, indem sie deren eventuelle wissenschaftliche Signifikanz belegt, die über ihre einfache statistische (In-) Signifikanz hinausgeht. Diese beiden Größen, Effektgröße und Teststärke, erlauben es andererseits, gewisse Resultate zu relativieren, die zwar statistisch signifikant sind (oft durch die Größe der Stichprobe, wie im zweiten Beispiel), aber deren Aussagekraft limitiert ist. Zu Beginn einer Forschungsarbeit können diese beide Größen auch zur Forschungsplanung beitragen, indem in der Planungsphase die notwendigen Stichprobengrößen berechnet werden. Schließlich kann die Effektgröße als Referenzgröße für Metaanalysen dienen.Power analysis and effect size are two statistical concepts, which are not widely used in sport sciences in spite of their relevance. This article shows, through two distinct studies, the numerous advantages of using these concepts. Using power analysis considerations, it becomes clear in the first study that one could not reach statistical significance due to the small sizes of the two samples. In this case, it seems better to rely on effect size to conclude because the effect size shows the actual importance of a phenomenon, emphasizing its scientific significance beyond the usual statistical (non) significance. On the contrary, the results of the second study are statistically significant because of the huge size of the sample but its explanatory power, as estimated by the observed effect size, is rather limited. These results have thus to be pondered. Effect size and power analysis are also very useful in experimental planning in order to determine adequate sizes for the samples to collect. Finally, the concept of effect size can be used to compare several studies in a meta-analysis.Les notions statistiques d’analyse de puissance et de taille d’effet sont encore très peu utilisées dans les sciences du sport, malgré leur pertinence et leur intérêt. Cet exposé illustre, au travers de deux études distinctes, les nombreux avantages qui peuvent être retirés de leur emploi. Le recours à ces deux notions vise d’une part à mettre en lumière les apports de certaines études se heurtant à un manque de significativité statistique (souvent lié à de petits échantillons, ce qui est le cas du premier exemple présenté) et pour lesquelles il est difficile, malgré leur intérêt réel, de pouvoir défendre les « conclusions ». La détermination de la taille d’effet, en particulier, met en avant l’importance concrète des effets mesurés, témoignant de leur éventuelle significativité scientifique, au-delà de leur simple (non-) significativité statistique. Ces deux notions, taille d’effet et analyse de puissance, permettent d’autre part de pouvoir relativiser certains résultats, pourtant statistiquement significatifs (souvent dus à la taille importante de l’échantillon, comme dans le deuxième exemple), mais dont le pouvoir explicatif s’avère limité. En amont de toute recherche, ces deux notions peuvent également contribuer à la planification des protocoles d’études, permettant ainsi de déterminer au préalable les tailles d’échantillons qui seraient nécessaires. Enfin, la taille d’effet peut servir de mesure de référence pour mener des comparaisons entre différentes études (favorisant ainsi les méta-analyses)

Méthodes statistiques globales et locales d'analyse d'un tableau de contingence par les tailles d'effet et leurs intervalles de confiance

International audienceThis paper presents global and local analyses of a contingency table along the lines of Wilkinson et al. (1999) defining good statistical practices as using effect sizes, confidence intervals and plots instead of tests of significance. On one hand, the global relationship between the two qualitative variables is measured by Cramer’s V. A confidence interval may be calculated using the decentred chi-squared distribution by inverting the corresponding significance test. A bootstrap confidence interval is also proposed. On the other hand, Cibois’s PEM (percentage of maximum deviation from independence) is a local effect size that can be computed for every cell of the contingency table giving its own distance from the independence hypothesis. A corresponding confidence interval is calculated by the previous resampling bootstrap technique. An original plot summarizing these pieces of information for the whole contingency table is proposed.Cet article propose une méthode d'analyse globale et locale d'un tableau de contingence suivant les « bonnes pratiques statistiques » comme définies par Wilkinson et al. (1999) c'est-à-dire en ayant principalement recours à des mesures de taille d'effet, des intervalles de confiance et des graphiques plutôt qu'à des tests de significativité. Au niveau global, la relation entre les deux variables qualitatives est mesurée par le V de Cramér. Un intervalle de confiance basé sur la loi du chi-carré décentrée peut être calculé par inversion du test de significativité. La méthode du bootstrap est également utilisée. Au niveau local, le PEM de Cibois (Pourcentage d'Ecart Maximum à l'indépendance) constitue une mesure de taille d'effet permettant d'estimer l'écart de chaque case du tableau de contingence à l'hypothèse d'indépendance. La procédure de ré-échantillonnage bootstrap en donne un intervalle de confiance. Un graphique original résumant ces informations pour l'ensemble du tableau est proposé