Utilidad de un nuevo sistema de cronometraje para proporcionar feedback inmediato a los nadadores

El presente documento tiene dos objetivos, en primer lugar, describir un nuevo sistema de cronometraje que proporciona feedback en tiempo real y sin interferir en la ejecución del nadador y, en segundo lugar, comprobar su utilidad. El sistema consiste en una pantalla de leds, resistente al agua e instalada en el fondo de la piscina, conectada a una Unidad Central mediante una plataforma de contacto colocada en la pared donde se realiza el viraje. La pantalla de leds informa al nadador de los tiempos y número de vueltas e, incluso, puede presentar texto (consignas) escrito por el entrenador. Este sistema se puede conectar a un PC o una PDA, permitiendo registrar los tiempos para su posterior análisis. Se comparó la eficacia del feedback proporcionado por este sistema, con la condición «feedback tradicional» y la condición «sin feedback», a ritmo de nado aeróbico. Los resultados muestran que la dispersión de los tiempos parciales los nadadores, es menor con el feedback proporcionado por el nuevo sistema

ANALYSIS OF TETHERED SWIMMING FORCE, TETHERED SWIMMING POWER, SWIMMING SPEED AND ANTROPOMETRICAL CHARACTERISTICS OF YOUNG SWIMMERS IN CRAWL STROKE

Propulsive forces, instantaneous power and swimming velocity in semi-tethered swimming were measured in a group of 69 competitive swimmers. Also, isometric force in laboratory, best 15 m swimming velocity and 100 m freestyle personal mark and anthropometric characteristics were recorded. The results show the high relationship between swimming speed and the propulsive forces, and the instantaneous power. Consequently, the above mentioned variables can be useful for the evaluation of the swimmers along a season

INFLUENCE OF FOOTWEAR ON THE ANKL SPRAIN PRODUCTION MECHANISM IN BASKETBALL

INTRODUCTION: Vertical jump is a usual movement pattern in basketball, and it is related to ankle injuries, mainly during rebound actions when falling on another player's foot. The aim of the present study IS to determine the influence of the introduction of certain elements in the footwear on ankle protection when falling on an irregular surface. The study consisted in simulating a rebound action in which the player jumps and falls on an irregular surface, simulated by a 20" inclined plane. 12 footwear prototypes were studied, making a factorial design with the following elements: high or low top, upper vamp stabilizer, hollow midsole at midfoot level and lace anchors. 3 test subjects, students of Physical Education, took part. They performed 36 jumps each, in series of 3, with a recovering time of 3 s between jumps and 3 m between series. Each series was done wearing one of the 12 prototypes at random. Each jump was filmed at 150 Hz and then digitized. The angles of knee and ankle were calculated as a function of time. For the statistical analysis an analysis of variance (ANOVA) was made, considering as factors the elements introduced in the footwear and a level of significance of 0,05 was chosen. RESULTS: The results indicate the high top footwear limited the range of movement during ankle flexion-extension and they produce higher values of inversion than low top. With an upper vamp stabilizer, higher values of inversion were obtained than without it. On the other hand, with a hollow midsole, inversion values were lower. Introducing a movement control system in the rearfoot, by means of lace anchors, did not show influence on the studied movements. CONCLUSIONS: In this way, after landing on an irregular surface, the high top as well as an upper vamp stabilizer increase the degree of inversion, probably because these elements rigidify vertically the footwear and increase the adherence to the floor or to the irregular surface on which the subject IS. However, it must be considered that epidemiological studies state that high top footwear diminish the risk of acute ankle injuries in basketball players. The upper vamp stabilizer, on the contrary, only rigidifies vertically the footwear and it dos not offer any extra reinforcement of the joint, increasing the risk of suffering ankle injuries. REFERENCES: Stacoff, A.; Kalin, X.; Stiitsi, E. (1 989) Torsional movements of the foot during landing. Abstracs of the XI1 Congress of the International Society of Biomechanics. Los Angeles, 1085. Sussman, D. H.; Hamill, J.; Miller, M. (1988) Effect of shoe height and prophylactic taping on ankle joint motion during s~mulated basketball rebounding. In De Groot, G., Hollander, A.P.; Huijing, P.A.; Van lngen Schenau, G.J. (Eds.) Biomechanics XI-6

S-duality in Twistor Space

In type IIB string compactifications on a Calabi-Yau threefold, the hypermultiplet moduli space $M_H$ must carry an isometric action of the modular group SL(2,Z), inherited from the S-duality symmetry of type IIB string theory in ten dimensions. We investigate how this modular symmetry is realized at the level of the twistor space of $M_H$, and construct a general class of SL(2,Z)-invariant quaternion-Kahler metrics with two commuting isometries, parametrized by a suitably covariant family of holomorphic transition functions. This family should include $M_H$ corrected by D3-D1-D(-1)-instantons (with fivebrane corrections ignored) and, after taking a suitable rigid limit, the Coulomb branch of five-dimensional N=2 gauge theories compactified on a torus, including monopole string instantons. These results allow us to considerably simplify the derivation of the mirror map between type IIA and IIB fields in the sector where only D1-D(-1)-instantons are retained.Comment: 29 pages, 1 figur

INFLUENCE OF THE FOOTBALL BOOT DESIGN ON SHOCK ABSORPTION

INTRODUCTION: A number of studies about the importance of sports shoe design on injuries prevention have been published in late years (Masson, 1989;Stacoff, 1988). Epidemiological studies indicate that football has special relevance with relation to suffering injuries (Hoff,1986; Ydes, 1990). During the practice of football a number of movement patterns such as jumping or running are performed(Reilly, 1976), being shock absorption a basic criterion for the design of footwear in Worts where such movement patterns occur. To improve the shock absorption of footwear two strategies are often adopted: to potentiate the natural mechanisms by means Of a better the tissue heel Or to increase the shock absorption capability of the footwear appropriately selecting the materials of the sole and insole. The aim the study was to evaluate the effect which different boot designs and different sole and insole materials had on load transMission during running. Based on a preliminary study, 3 boot prototypes and 4 insole prototypes were made. 8healthy football players were selected and they performed 6 runs with each of the 12possible combinations of boot/insole. The runs were performed in a football field and a speed of 4 m/s was determined controlled by electric photocells. The sequence of each condition was randomized for each subject. The subjects were instrumented with 2 accelerometers, attached to their skin by means of a strong bandage on tibia and forehead. The signals from the accelerometers were connected to a telemetry equipment which allowed the subject freer movements. With parameters obtained, an analysis of variance (ANOVA) was made. The level of significance chosen was of alfa < 0.05. To analyze the differences between conditions, an LSD test was made. RESULTS: One of the viscoelastic materials inserted in the insole offered a mean reduction of impacts of about 6%.One of' the materials of the boot sole showed a better capability of shock absorption, about 7%. The boots to which a special compartment for the heel pad did not improve shock absorption. Acceleration measured at tibia was of 6.01+0.06 times gravity (g) and at head it was of 2.45+2g.CONCLUSION: According to the results, an appropriate selection of insole and boot materials an improvement of shock absorption of 13% can be obtained. Although the tests were made on a natural grass football field and the speed of run was not too high, the values found for both tibia and forehead were high: this fact confirms the hypothesis that shock absorption is a basic criterion in the design of football boots from the point of view of protection from injuries. REFERENCES: Hoff, G.L and Martin, T.A.(1986). Outdoor and Indoor soccer: Injuries among youth players. Am. J. Sp. Med. 8,231-233.Masson, M. and Hess, H. (1989) Typicalsoccer injuries. Their effects on the design of the athletic shoe. In 6. Segesser & W.Pforringer (Eds.) The shoe in sport.London: Wolfe Publishing, Lld., 89-95.Reilly, T. (1 976) A motion analysis of work rate in differential roles in professional football match play. J. Human Mov. Stud.2, 87-97.Stacoff, A,; Denoth, J.; Kaelin, X. and Stuessi, E. (1988) Running injuries and shoe construction: Some possible relantionships. lnt. J. Sports Biomech. 4,342-357.Yde, J. and Nielsen, A.B. (1990) Sport injuries in adolescents' ball games: soccer,handball and basketball. Br. J. Sp. Med24(1), 51-54.8

INFLUENCE OF MIDSOLE CONSTRUCTION AND UPPER VAMP DESIGN IN THE PRONATION MOVEMENT WHILE RUNNING

The relationship between the excessive rearfoot pronation and some injuries has been widely described in the literature (Bates, Cavanagh, Nigg, Stacoff). The influence of midsole design and material in the amount of pronation has also been analyzed by different authors. Nevertheless the relative influence of midsole and upper vamp design and their interactions have not been studied enough. The aim of the study presented was to investigate the relative effect of midsole material and thickness as well as upper vamp systems in controlling pronation. Twelve prototypes of running shoes were specially designed and constructed for this study. The prototypes corresponded to a factorial experiment design of the following factors: two midsole thicknesses, three midsole materials, and the presence or absence of an external heel counter and post. The materials selection was based on a previous study of the mechanical characteristics of a group of different Poliurethanes with different densities. The stiffness and energy absorbing capacity of the materials were previously studied by simulating impact loads of running by means of a dynamic testing machine. The external heel counter and post was selected as a representative of a very effective rearfoot control feature based in a previous study where it appeared to be the most effective system of the studied (heel counters, bondings for the lacing and internal posts). Three runners participated in the study. All of them were rearfoot strikers and hiperpronators. The experiences consisted of filming three right foot supports with two high speed cameras. Velocity of running was fixed at 12.8 Km per hour while velocity of filmation was fixed at 150 images per second. After digitizing the images obtained, a three dimensional study of the rearfoot movement was done. The results obtained can be summarized as follows: - Midsole thickness, midsole material and the presence of the heel counter showed significant influence on maximum rearfoot pronation with the most important being the midsole material in the range of variations of the study. - The material presenting low rigidity and low shock absorbing capacity was the one that showed higher pronation angles. - Higher pronation angles were found for the thicker midsoles. - The heel counter and post was found to have less influence on maximum pronation angles than the midsole thickness and material