Andrea Michele Freudenheim

Control of striking velocity by table tennis players.

This study investigated how 7 skilled table tennis players controlled velocity of a forehand drive stroke when the balls trajectory, velocity, and spin were modified. They hit a target in response to balls launched under four different conditions. The relative and absolute times used in the backswing phase showed no significant differences among conditions. When subjects hit fastballs, there was a significant change in the time required for them to reach the peak of velocity in the forward swing phase. In addition, players decreased the velocity of their strokes to hit fast-approaching balls. These results indicate that highly skilled table tennis players need to adjust the striking velocity and striking time (relative and absolute) required to reach the peak of velocity in the forward swing phase for these task modifications. Since they used slower movement velocities to hit faster-approaching balls, skilled table tennis players may override this speed-coupling process.

“Timing” coincidente em tarefas complexas: estudo exploratório do desempenho de adultos de diferentes idades em diferentes velocidades de estímulo visual

O objetivo desse estudo foi investigar o desempenho em uma tarefa complexa de “timing” coincidente em funcao da idade e da velocidade do estimulo visual. Os participantes foram 58 adultos voluntarios de ambos os sexos (38 adultos jovens com idades entre 19 e 23 anos e 20 adultos maduros com idades entre 35 e 50 anos). Cada grupo de adultos foi dividido em tres subgrupos de acordo com uma velocidade do estimulo visual (lenta, moderada e rapida). A tarefa consistiu em tocar cinco alvos em uma ordem pre-estabelecida em integracao a um estimulo visual. A variavel dependente foi o erro (absoluto, variavel e constante). Os dados foram analisados por meio de estatistica nao-parametrica, sendo que a ANOVA de Kruskal-Wallis apontou diferenca entre os grupos apenas no erro constante. Todavia, o teste U de Mann-Whitney, com o p ajustado com o procedimento de Bonferroni nao foi capaz de identificar entre quais grupos houve diferenca. Pode-se concluir que adultos jovens e maduros obtiveram similar desempenho em uma tarefa complexa de “timing” coincidente, independentemente da velocidade do estimulo visual.

Health-related physical fitness children with severe and moderate developmental coordination disorder

The present study aims to examine physical fitness among children with developmental coordination disorder (DCD) with varying degrees of severity (moderate and severe - mDCD, sDCD), and a group of children without DCD (wDCD), in the city of Manaus, Brazil. Initially, 180 children aged 6-10 years old participated in this study. After being diagnosed according to the DSM-IV-TR, 63 children were then divided into three groups (21 in each group). Health-related physical fitness was measured by means of the Fitnessgram, which included several core components, namely, body composition, muscle strength and endurance, flexibility, and cardiorespiratory resistance. The results showed no statistically significant differences between both groups in any of the assessed components. However, when analyzing the results of each component according to the criteria of the Fitnessgram, we observed that, regardless of the classification group, less than half of the children achieved scores that, according to the motor tests, would classify them as having a healthy fitness. Children with sDCD, mDCD and wDCD presented similar levels of health-related physical fitness, with an unsatisfactory performance for the component strength and muscular endurance. We therefore emphasize the importance of further research in this area, more particularly when it comes to following the development of motor skills and physical fitness in children with DCD, as well as the observation of the interactions between these variables over time.

Organizaçäo hierarquica e a estabilizaçäo de um programa de açäo: um estudo exploratório

O objetivo deste estudo foi investigar a estabilizacao de uma habilidade motora grafica. Assumiu-se que a estabilizacao corresponderia a formacao de um programa de acao hierarquicamente organizado. Em conseguencia, que a macro-estrutura do programa seria mantida enquanto a micro-estrutura do programa variaria frente a pertubacoes. Participaram tres estudantes universitarias que praticaram 83 blocos de 10 tentativas, na tarefa de reproduzir um padrao grafico. No 80 bloco foi introduzida uma modificacao na tarefa. Foram utilizadas medidas relacionadas ao desempenho global, a variabilidade da macro-estrutura. Com a pratica houve diminuicao da variabilidade do nivel macro, bem como, coincidencia entre os momentos de inicio dos patamares das medidas de desempenho global e de variabilidade na macro-estrutura. Houve uma rapida recuperacao apos a modificacao da tarefa, posto que o desempenho retornou prontamente aos niveis pre pertubacao. Estes resultados estao de acordo com a ideia de que a estabilizacao implica na formacao de uma macro-estrutura consistente, i.e., de um programa de acao organizado hierarquicamenteThe purpose of this study was to investigate the stabilization of a graphic skill. It was assumed that stabilization would correspond to the formation of a hierarchically organised action programme. Accordingly, it was expected that the programme’s macro-structure would be maintained while the programme’s microstructure would vary in face of perturbations. Three university students practised 83 blocks of 10 trials in order to reproduce a graphic pattern. At the 80th block the task was modified. Measures related to global performance, macro and micro variability, were utilised. With practice there was a decrease in variability on the macro level, as well as a coincidence between the moments when the global performance measure and the macro variability measure plateaus began. There was a quick recovery after task, since performance returned promptly to the levels shown before perturbation. Those results are in agreement with the idea that stabilization implies in the formation of a consistent macro-structure, ie. of a hierarchically organized action programme

Validação de um instrumento para avaliação qualitativa do nado “Crawl”

The lack of instruments to evaluate the crawl stroke, based on recent assumptions regarding technical efficiency and range of styles for a single stroke, has posed difficulties to both swimming coaches and motor behavior researchers. The objective of this study was to propose and validate an instrument for evaluating Crawl stroke qualitatively. A proficiency list with the most frequent technical errors was elaborated, ranked according to the sub-components of the stroke in twelve categories. In order to perform the validation of the instrument, seven childrens (four boys and three girls), with at least one year of swimming experience and age of 10.5 (±2) years, had their displacements videotaped (above and underwater). Three competitive swimming experts, with academic graduation, evaluated the content of the checklist. Then, intra- and inter-examiners correlations were determined. The results confirmed that the content of the list showed clarity and satisfactory technical pertinence and good applicability. As for consistency and reproducibility, it is possible to infer that the checklist is adequate since the intra-examiner correlation was between 0.83 and 1.0 and 91% of the correlations were above 0.9. The inter-examiner correlation, on the other hand, was between 0.50 and 1.0 with 90% of the correlation above 0.9. Thus, the checklist used to evaluate the proficiency level for the proposed stroke seems to be valid and to take into account individual differences, magnitude and meaning of the technical erros.

Number of options in a movement sequence affects learners' behavior in a self-controlled practice condition.

Self-controlling practice implies a process of decision making, which suggests that the options in a self-controlled practice condition could affect learners. The number of task components with no fixed position in a movement sequence may affect the way learners self-control their practice. A 200-cm coincident timing track with 90 light-emitting diodes (LEDs) — the first and the last LEDs being the warning and the target lights, respectively — was set so that the apparent speed of the light along the track was 1.33 m/sec. Participants were required to touch six sensors sequentially, the last one coincidently with the lighting of the target light (timing task). Group 1 (n = 55) had only one constraint, and were instructed to touch the sensors in any order, except for the last sensor which had to be the one positioned close to the target light. Group 2 (n = 53) had three constraints: the first two and the last sensor to be touched. Both groups practiced the task until timing error was less than 30 msec. on three consecutive trials. There were no statistically significant differences between groups in the number of trials needed to reach the performance criterion, but (a) participants in Group 2 created fewer sequences compared to Group 1, and (b) were more likely to use the same sequence throughout the learning process. The number of options for a movement sequence affected the way learners self-controlled their practice, but had no effect on the amount of practice to reach criterion performance.

Aquisição da habilidade motora rebater na educação física escolar: um estudo das dicas de aprendizagem como conteúdo de ensino

O objetivo do estudo foi investigar o efeito das dicas verbais na aquisicao da habilidade rebater na Educacao Fisica Escolar (EFE), com foco de atencao no seu aspecto perceptivo e motor. Participaram do estudo 84 alunos de tres turmas de uma escola (faixa etaria entre seis a oito anos). Cada turma correspondeu a um grupo: sem dicas, com dica perceptiva e com dica motora. O experimento teve tres fases: pre-teste, aulas de EFE e pos-teste. O grupo com dica perceptiva apresentou melhores resultados. Portanto, verificou-se o efeito das dicas relacionado com a especificidade da tarefa no que se refere as suas demandas de processamento. Assim concluiu-se que a dica de aprendizagem relacionada a especificidade da tarefa mostrou o seu potencial como um conhecimento que orienta os alunos em direcao a melhoria da qualidade do movimento, confirmando a possibilidade de sua inclusao como conteudo de ensino da EFE.

Assessment of Beginners' Front-Crawl Stroke Efficiency:

Efficiency in front-crawl stroke has been inferred primarily by means of the analysis of arm actions, specifically, stroke frequency and stroke length. The objective of the present study was to investigate whether swimming efficiency could be better assessed in children still learning the front-crawl stroke by analyzing the movement pattern as a whole. Forty-two children enrolled in private swimming programs volunteered to participate in the study. The task consisted of swimming 30 m as fast as possible. Three experts analyzed the movement pattern of the participants using a checklist. Both stroke frequency and stroke length were calculated. The correlation coefficients between the time taken to swim and both the stroke frequency and stroke length were not significant, but the total and components of the checklist scores were. Results indicate that the swimming efficiency of children learning the front-crawl stroke can be better assessed by analyzing their whole movement pattern.

Estrutura de prática e validade ecológica no processo adaptativo de aprendizagem motora

O objetivo desse estudo foi investigar o efeito da estrutura de pratica no processo adaptativo de aprendizagem motora em funcao da validade ecologica da situacao experimental. Participaram do estudo 104 criancas distribuidas em oito grupos experimentais (dois niveis de validade ecologica x quatro estruturas de pratica). A tarefa consistiu em rebater uma bola de tenis de mesa lancada por um equipamento ou pelo experimentador, com o objetivo de acertar um alvo localizado no lado oposto da mesa. O estudo envolveu duas fases: estabilizacao e adaptacao. O desempenho foi analisado por meio da soma dos pontos obtidos em blocos de 10 tentativas. Os resultados mostraram que os efeitos das praticas constante, aleatoria, constante-aleatoria e aleatoria-constante no processo adaptativo de aprendizagem motora foram similares em ambos os niveis de validade ecologica; a pratica constante foi a estrutura menos efetiva no processo adaptativo de aprendizagem motora em ambas as situacoes experimentais.

Análise sistêmica do nado Crawl

The purpose of this study was to investigate the front crawl stroke at a behavioral level, ie arm stroke, leg stroke, and breathing components both separately and in interaction. Eleven adults aged 28 (P 4.25), experienced in front crawl stroke participated. They swam 10 meters at high speed and l0 meters at low speed. At both speeds, the variabilities of whole and parts were the measures considered. Data was analyzed through a Wilcoxon test, considering the following comparisons: whole versus parts at high speed; whole versus parts at low speed; whole at high speed versus whole at low speed; and parts at high speed versus at low speed. Results showed that at low speed the variability of parts was significantly superior to the variability of the whole, and therefore, that in interaction the behavior of arm stroke, leg stroke, and breathing varied less than each separately. Key Words: Performance, system, swimming, front crawl stroke.