Regulación del movimiento y anticipación en el resto del primer servicio en tenis

Aunque se han logrado importantes avances en estudios de laboratorio con diseños experimentales poco representativos (e.g., Farrow y Reid, 2012; Nieminen, Piirainen, Salmi, y Linnamo, 2013), a día de hoy, todavía se desconoce a cabalidad cómo los jugadores de tenis de diferente nivel de pericia calibran o ajustan sus movimientos a las demandas espacio-temporales presentes en la tarea de resto de un primer servicio. ! Escasos trabajos se han llevado a cabo in situ y a la mayoría se les puede cuestionar algún aspecto de la metodología empleada. Así pues, en varios estudios la frecuencia de grabación ha sido limitada (e.g., a 50 Hz en Jackson y Gudgeon, 2004; Triolet, Benguigui, Le Runigo y Williams, 2013), o la velocidad del saque ha sido visiblemente inferior a la habitual (cf. Carboch, Süss y Kocib, 2014; Williams, Singer y Weigelt, 1998). También, en algunos estudios los participantes experimentados no han sido jugadores de nivel internacional (e.g., Avilés, Ruiz, Sanz y Navia, 2014), y el tamaño muestral ha sido muy pequeño (e.g., Gillet, Leroy, Thouvarecq, Mégrot y Stein, 2010). ! Además, en los diferentes trabajos se han utilizado una diversidad de métodos e instrumentos de medida y los criterios de codificación del inicio de los movimientos y de las respuestas han diferido; como consecuencia el lapso visomotor de respuesta (LVMr) ha sido muy dispar variando considerablemente de 198 a 410 ms. Considerando los inconvenientes señalados anteriormente, el presente estudio tuvo como objetivo determinar un modelo técnico de regulación temporal de los movimientos y de la respuesta del restador, tomando en cuenta el flujo continuo de información proporcionado por el sacador. Para ello, se realizó un análisis cronométrico de los restos de doce jugadores de diferente nivel deportivo (seis internacionales y seis nacionales) que respondieron de forma natural enviando sus devoluciones hacia las dianas. Se grabaron las acciones de los restadores y sacadores con una cámara Casio Exilim Pro Ex-F1 de alta velocidad (300 Hz) y luego se realizó un análisis imagen por imagen cada 3.33 ms. Una vez obtenidos los datos de los vídeos se realizaron análisis con las pruebas de ANOVA de un factor, ANCOVA con la velocidad del saque como covariable, U de Mann-Whitney y Chi-cuadrado de Pearson. En cuanto a la regulación del movimiento hasta el momento del despegue, los jugadores internacionales iniciaron sus acciones antes que los jugadores nacionales lo que podría indicar una mejor preparación al ejecutar los movimientos como reflejo del nivel de pericia. Los jugadores internacionales iniciaron la elevación del pie posterior a -293 ms y los jugadores nacionales a -202 ms. Todas estas acciones se fueron enlazando unas con otras y fue en el momento del impacto del sacador donde los restadores demostraron una remarcable coordinación perceptivo-motriz. Por consiguiente, los jugadores internacionales despegaron e iniciaron el vuelo a tan solo -6.5 ms del impacto y los jugadores nacionales lo hicieron más tarde a +19.5 ms. A lo largo de la secuencia temporal, todo parece indicar que las informaciones que utilizan los restadores interactúan entre sí; información más temprana y menos fiable para anticipar o moverse antes e información más tardía y más fiable para regular la temporalización de las acciones. Los restadores de nivel internacional y nacional anticiparon a nivel espacial en un bajo porcentaje (7.7% vs. 13.6%) y en tiempos similares (-127 vs. -118 ms) sugiriendo que la utilización de variables ópticas tempranas y menos fiables solo se produce en contadas ocasiones. Por otra parte, estos datos se relacionan con una gran precisión en la respuesta ya que tanto los jugadores internacionales como los nacionales demostraron un alto porcentaje de acierto al responder (95.4% vs. 96.7%). Se había señalado que los jugadores internacionales y nacionales se diferenciarían en el tiempo de caída (i.e., aterrizaje) del primer pie del salto preparatorio, sin embargo ese efecto no fue encontrado (128 vs. 135 ms). Tampoco se hallaron diferencias en el porcentaje de caída con el pie contrario a la dirección de la pelota (58% vs. 62%). Donde sí ambos grupos se diferenciaron fue en el tiempo de caída del segundo pie (147 vs. 168 ms). Esta diferencia de 21 ms fue crucial y fue una prueba de la mayor rapidez de los jugadores internacionales; sugiriendo que ésta acción se podría relacionar con el momento del inicio de la respuesta. Aunque los jugadores internacionales hayan demostrado ser más rápidos en relación con sus capacidades funcionales, ambos grupos no se diferenciaron en todas las variables relacionadas con el LVMr. Ellos no utilizaron esos valiosos milisegundos ganados en el instante de la caída del segundo pie para responder más pronto, ya que el LVMr del miembro superior fue el mismo para ambos grupos (179 vs. 174 ms). Es como si hubiesen tenido todo el tiempo del mundo para seguir ajustando sus acciones hasta el propio golpeo. Además, estos tiempos largos sugieren que en la gran mayoría de los restos la información clave que determinó la respuesta fue detectada (extraída) en momentos cercanos al golpeo del sacador y en la primera parte del vuelo de la pelota. Asimismo, se constató que en general el LVMr se ve influenciado por el tipo de información utilizada. De esta manera, cuando se tomaron en cuenta los ensayos en los que hubo anticipación espacial reflejados en el LVMr del cuerpo entero los tiempos disminuyeron (152 vs. 136 ms). Por otra parte, existieron ocasiones (13%) en los que tanto los jugadores internacionales como los nacionales respondieron tarde recibiendo saques directos (208 vs. 195 ms). Es muy posible que en estos casos los jugadores hayan tenido problemas para detectar la información respondiendo fuera de los márgenes temporales de acción lo que mermó su rendimiento. Lo mismo pudo haber ocurrido cuando ambos grupos de jugadores corrigieron el movimiento del miembro superior tras el impacto (17% vs. 10%) lo que aumentó el tiempo en responder al redirigir la respuesta hacia el lado correcto (208 vs. 205 ms). Además, los jugadores internacionales obtuvieron tiempos de movimiento menores que el de los jugadores nacionales (509 vs. 531 ms) lo que se reflejó en un tiempo total de actuación menor (683 vs. 703 ms). Por último, en cuanto al rendimiento del resto, los jugadores internacionales obtuvieron valores superiores a los jugadores nacionales (1.3 vs. 0.9). ABSTRACT Although there have been significant advances in laboratory studies with unrepresentative experimental designs (e.g., Farrow y Reid, 2012; Nieminen, Piirainen, Salmi, y Linnamo, 2013), today it is still unknown to full extent how tennis players of different levels of expertise calibrate or adjust their movements to the spatial-temporal demands present in the return of a first serve. Few studies have been carried out in situ and some aspects of the methodology most of them used can be questioned. Thus, in several studies the recording frequency has been limited (e.g., a 50 Hz en Jackson y Gudgeon, 2004; Triolet, Benguigui, Le Runigo y Williams, 2013), or serve speed was visibly lower than the usual one (cf. Carboch, Süss y Kocib, 2014; Williams, Singer y Weigelt, 1998). Also, in some studies, experienced participants have not played at international level (e.g., Avilés, Ruiz, Sanz y Navia, 2014), and the sample size has been very small (e.g., Gillet, Leroy, Thouvarecq, Mégrot y Stein, 2010). Furthermore, different works have used a variety of methods and measurement instruments and coding criteria of the onset of movements and responses have differed; due to this, visuomotor response delay (LVMr) has been very uneven, varying considerably from 198-410 ms. Considering the drawbacks mentioned above, this study aimed to determine a technical model of temporal regulation of movements and returner’s response, taking into account the continuous flow of information provided by the server. For this, a chronometric analysis of the returns of twelve players (six international and six national) of different sports level, that naturally responded by hitting their returns towards the targets, was performed. Actions of servers and returners were recorded with a Casio Exilim Pro Ex-F1 high speed camera (300 Hz) and then every 3.33 ms analysis was made frame by frame. Once the data of the videos were obtained, analyses were performed using one factor ANOVA test, ANCOVA with the speed of the serve as a covariate, U of Mann- Whitney and Pearson’s Chi-square test. As for the regulation of movement until the moment of serve, international players began their actions before national players, which could indicate that they were better prepared to execute movements reflecting the level of their expertise. International players began raising the rear foot at -293 ms and national players at -202 ms. All these actions were being linked to each other and it was at the moment of impact of the server when the receivers demonstrated a remarkable perceptual-motor coordination. Therefore, international players took off and started their flight just -6.5 ms before the serve and national players did the same somewhat later: +19.5 ms after the serve. Along the timeline, everything seems to indicate that the information used by returners interact with each other; early information which is less reliable to anticipate or move before, and later information more reliable appears to regulate the timing of actions. Returners of international and national levels anticipated at spatial level in a low percentage (7.7% vs. 13.6%) and in similar times (-127 vs. -118 ms) suggesting that the use of early and less reliable optical variables is only produced on rare occasions. Moreover, these data relate to a precise response as both international and national players showed a high percentage of success in responding (95.4% vs. 96.7%). It had been noted that international and national players would differ in the time the fall (i.e., landing) of the first foot of the split-step, however, this effect was not found (128 vs. 135 ms). No differences in the percentage of fall with the opposite foot to the direction of the ball (58% vs. 62%) were found. Where the two groups differed was in the time of the fall of the second foot (147 vs. 168 ms). This difference of 21 ms was crucial and it was a proof of mayor speed of international players; suggesting that this action could be related to the onset time of response. Although international players have proven to be faster in relation to their functional capabilities, both groups did not differ in all variables related to LVMr. They did not use those precious milliseconds earned at the time of the fall of the second foot to respond as soon, since the LVMr of the upper limb was the same for both groups (179 vs. 174 ms). It is as if they had all the time in the world to continue to adjust their actions until the return itself. Furthermore, these long times suggest that in the vast majority of the returns, key information that determined the response was detected (pick-up) in moments close to the hit of the server and in the first part of the ball flight. It was also found that in general the LVMr is influenced by the type of information used. Thus, when taking into account the trials during which there was spatial anticipation, reflected in LVMr of the whole body, the times decreased (152 vs. 136 ms). On the other hand, there were occasions (13%) where both international and national players responded late, thus receiving aces (208 vs. 195 ms). It is quite possible that in these cases the players have had trouble to pick-up information, responding out of temporary margins of action, which affected their performance. The same could have occurred when both groups of players corrected upper limb movement after impact (17% vs. 10%), which increased the time to respond and to redirect the return towards the right side (208 vs. 205 ms). Moreover, international players scored lower movement times than the national players (509 vs. 531 ms), which was reflected in a shorter total response time (683 vs. 703 ms). Finally, as far as the performance of return is concerned, international players scored above the national players values (1.3 vs. 0.9).

Players Redux: A Cyclical History of World Trade Center

Articulo publicado con ocasión de los 10 años del 9/11, el día 11.09.2011 en portada de edición on-line. ... The towers seemed provisional to Pammy. They remained mere concepts, not because their excessive volume less temporary than any regular distortion of light.

Acute effects of endurance exercise on jumping and kicking performance in top-class young soccer players

The aim of this study was to examine the acute effects of endurance exercise on jumping and kicking performance in young soccer players. Twenty-one top-class young soccer players (16.1±0.2 years) performed a countermovement jump test and a maximal instep soccer kick test before and after running for 20 min on a treadmill at 80% of their individual maximum heart rate. Two force platforms were used to obtain the following parameters during the countermovement jump: jump height, maximum power, maximum power relative to body mass, maximum vertical ground reaction force, maximum vertical ground reaction force relative to body mass, and maximum vertical ground reaction force applied to each leg. Maximum vertical ground reaction force and maximum vertical ground reaction force relative to body mass applied to the support leg during the kicks were also calculated with a force platform. The kicking motion was recorded using a three-dimensional motion-capture system. Maximum velocity of the ball, maximum linear velocity of the toe, ankle, knee and hip, and linear velocity of the toe at ball contact during the kicks were calculated. Non-significant differences were found in the parameters measured during the countermovement jump and the maximal instep soccer kick test before and after running, suggesting that the jumping and kicking performances of top-class young soccer players were not significantly affected after 20 min treadmill running at 80% of their individual maximum heart rate.

Co-evolutionary and Reinforcement Learning Techniques Applied to Computer Go players

The objective of this thesis is model some processes from the nature as evolution and co-evolution, and proposing some techniques that can ensure that these learning process really happens and useful to solve some complex problems as Go game. The Go game is ancient and very complex game with simple rules which still is a challenge for the Artificial Intelligence. This dissertation cover some approaches that were applied to solve this problem, proposing solve this problem using competitive and cooperative co-evolutionary learning methods and other techniques proposed by the author. To study, implement and prove these methods were used some neural networks structures, a framework free available and coded many programs. The techniques proposed were coded by the author, performed many experiments to find the best configuration to ensure that co-evolution is progressing and discussed the results. Using co-evolutionary learning processes can be observed some pathologies which could impact co-evolution progress. In this dissertation is introduced some techniques to solve pathologies as loss of gradients, cycling dynamics and forgetting. According to some authors, one solution to solve these co-evolution pathologies is introduce more diversity in populations that are evolving. In this thesis is proposed some techniques to introduce more diversity and some diversity measurements for neural networks structures to monitor diversity during co-evolution. The genotype diversity evolved were analyzed in terms of its impact to global fitness of the strategies evolved and their generalization. Additionally, it was introduced a memory mechanism in the network neural structures to reinforce some strategies in the genes of the neurons evolved with the intention that some good strategies learned are not forgotten. In this dissertation is presented some works from other authors in which cooperative and competitive co-evolution has been applied. The Go board size used in this thesis was 9x9, but can be easily escalated to more bigger boards.The author believe that programs coded and techniques introduced in this dissertation can be used for other domains.

Training-induced changes in drag-flick technique in female field hockey players

The penalty corner is one of the most important goal plays in field hockey. The drag-flick is used less by women than men in a penalty corner. The aim of this study was to describe training-induced changes in the drag-flick technique in female field hockey players. Four female players participated in the study. The VICON optoelectronic system (Oxford Metrics, Oxford, UK) measured the kinematic parameters of the drag-flick with six cameras sampling at 250 Hz, prior to and after training. Fifteen shots were captured for each subject. A Wilcoxon test assessed the differences between pre-training and post-training parameters. Two players received specific training twice a week for 8 weeks; the other two players did not train. The proposed drills improved the position of the stick at the beginning of the shot (p<0.05), the total distance of the shot (p<0.05)and the rotation radius at ball release (p<0.01). It was noted that all players had lost speed of the previous run. Further studies should include a larger sample, in order to provide more information on field hockey performance.

Evolving and coevolving computer go players using neuroevolution.

The Go game is ancient very complex game with simple rules which still is a challenge for the AI.This work cover some neuroevolution techniques used in reinforcement learning applied to the GO game as SANE (Symbiotic Adaptive Neuro-Evolution) and presents a variation to this method with the intention of evolving better strategies in the game. The computer Go player based in SANE is evolved againts a knowed player which creates some problem as determinism for which is proposed the co-evolution. Finally, it is introduced an algorithm to co-evolve two populations of neurons to evolve better computer Go players.

Diseño y validación de un cuestionario socio-emocional para jóvenes futbolistas de élite. Desing and validation of a socio-emotional questionnaire for yourh footbal players

Validación de un cuestionario socio-emocional en fútbol

Kinematic and heart rate demands in 4x4 vs 7x7 small sided games in professional soccer players

Comparación de las variables cinemáticas y de frecuencia cardiaca en dos posesiones en fútbol

Analysis of dehidration and strenth in elite badminton players

Background: The negative effects of dehydration on aerobic activities are well established. However, it is unknown how dehydration affects intermittent sports performance. The purpose of this study was to identify the level of dehydration in elite badminton players and its relation to muscle strength and power production. Methodology: Seventy matches from the National Spanish badminton championship were analyzed (46 men?s singles and 24 women?s singles). Before and after each match, jump height and power production were determined during a countermovement jump on a force platform. Participants? body weight and a urine sample were also obtained before and after each match. The amount of liquid that the players drank during the match was also calculated by weighing their individual drinking bottles. Results and Discussion: Sweat rate during the game was 1.1460.46 l/h in men and 1.0260.64 l/h in women. The players rehydrated at a rate of 1.1060.55 l/h and 1.0160.44 l/h in the male and female groups respectively. Thus, the dehydration attained during the game was only 0.3760.50% in men and 0.3260.83% in women. No differences were found in any of the parameters analyzed during the vertical jump (men: from 31.8265.29 to 32.9064.49 W/kg; p.0.05, women: from 26.3664.73 to 27.2564.44 W/kg; p.0.05). Post-exercise urine samples revealed proteinuria (60.9% of cases in men and 66.7% in women), leukocyturia (men = 43.5% and women = 50.0%) and erythrocyturia (men = 50.0% and women = 21.7%). Conclusions: Despite a moderate sweat rate, badminton players adequately hydrated during a game and thus the dehydration attained was low. The badminton match did not cause muscle fatigue but it significantly increased the prevalence of proteinuria, leukocyturia and erythrocyturia.

Self perception of decision making competence in spanish football players

Background: It is known that competence to make decisions is a fundamental aspect of sport competition. Objective: This study has analyzed the decision profile of a sample of Spanish football players of different levels of expertise. Methods: 690 Spanish football players of national and international level completed the decision making questionnaire, which cover three dimensions ? perceived decision competence, decision anxiety and commitment with decision learning. MANCOVA and ANOVA analysis were carried out to analyse the differences in each dimension based on the level of expertise. Results: Results showed that perception of decision making competence increased and the anxiety decreased with the level of expertise. Conclusions: This study confirmed the usefulness of this questionnaire in the process of training for coaches and sport psychologists.

Time-motion analysis on Chinese male field hockey players

The aim of the study was to evaluate the match work-rate of Chinese field hockey players by analyzing the distance covered at different intensities pooled by specific positions during different periods of matches. Thirty-eight players from twenty-four male field hockey matches at the 11th Chinese National Games were filmed and analyzed.

Time-motion analysis on Chinese male field hockey players

The aim of the study was to evaluate the match work-rate of Chinese field hockey players by analyzing the distance covered at different intensities pooled by specific positions during different periods of matches. Thirty-eight players from twenty-four male field hockey matches at the 11th Chinese National Games were filmed and analyzed.mas

Self-perceptions of decision making competence in Spanish football players

Background: It is known that competence to make decisions is a fundamental aspect of sport competition. Objective: This study has analyzed the decision profile of a sample of Spanish football players of different levels of expertise. Methods: 690 Spanish football players of national and international level completed the decision mak- ing questionnaire, which cover three dimensions ? perceived decision competence, decision anxiety and commit- ment with decision learning. MANCOVA and ANOVA analysis were carried out to analyse the differences in each dimension based on the level of expertise. Results: Results showed that perception of decision making competence increased and the anxiety decreased with the level of expertise. Conclusions: This study confirmed the usefulness of this questionnaire in the process of training for coaches and sport psychologists.

Eccentric Exercise in Treatment of Patellar Tendinopathy in High Level Basketball Players. A Randomized Clinical Trial.

Chronic patellar tendinopathy is a common pathology in sporting population. To date, there is no agreed upon protocol as election treatment. Eccentric exercises have been used with satisfactory outcomes (3). The purpose of this trial was to compare the effects of two eccentric exercise protocols.

Eccentric exercise in treatment of patellar tendinopathy in high level basketball players. A randomized clinical trial

Chronic patellar tendinopathy is a common pathology in sporting population. To date, there is no agreed upon protocol as election treatment. Eccentric exercises have been used with satisfactory outcomes.