Tennis Rackets Research Articles

Transfer of tennis racket vibrations onto the human forearm

One of several factors suspected in the development of lateral epicondylitis, often referred to as tennis elbow, is the impact-induced vibration of the racket-and-arm system at ball contact. Using two miniature accelerometers at the wrist and the elbow of 24 tennis players, the effects of 23 different tennis racket constructions were evaluated in a simulated backhand stroke situation. The influences of body weight, skill level, and tennis racket construction onto the magnitude of vibrations at wrist and elbow were investigated. Amplitudes, integrals, and fourier components were used to characterize arm vibration. More than fourfold reductions in acceleration amplitude and integral were found between wrist and elbow. Off-center as compared with center ball impacts resulted in approximately three times increased acceleration values. Between subjects, body weight as well as skill level were found to influence arm vibration. Compared with proficient players, a group of less skilled subjects demonstrated increased vibration loads on the arm. Between different racket constructions, almost threefold differences in acceleration values could be observed. Increased racket head size as well as a higher resonance frequency of the racket were found to reduce arm vibration. The vibration at the arm after ball impact showed a strong inverse relationship (r = -0.88) with the resonance frequency of tennis rackets.

Why We Don't Have a Room-Temperature Superconductor—Yet: 1991 MRS Fall Von Hippel Award Address

I would like to raise a question of interest to many of us here today: “Why have we not been able to find a room-temperature superconductor?” I have a scenario for why not that can be illustrated by projecting ahead 98 years. It is 2089, the tercentenary of the French Revolution. The revolt against science that started building up in the last decade of the 20th century has reached a crescendo and a revolutionary tribunal has erected a huge guillotine. Following in the tradition of Lavoisier's trial and execution, the presidents of the Materials Research Society, the American Chemical Society, and the American Physical Society have been found to be enemies of the people and have been sentenced to be guillotined. The president of the Materials Research Society steps up. In his final words, he says: “I have no regrets. We've supplied you with the pole vaults which have made possible a new world's record above 30 feet, we've given you automobile bumpers that prevent damage in crashes at 60 miles per hour, and we've given you tennis rackets that are big enough to allow you to cover from center court to the alley without having to take a step.” With that, he bravely puts his head on the block. Down crashes the knife but inexplicably it stops just before it reaches his neck. According to the rules he steps down a free man. Then the American Chemical Society president steps up and says: “I don't have any regrets either. We have given you body centered cubic diamond that makes it possible to build indestructible houses, we have given you disposable diapers that are biodegradable in 30 seconds, and we've reseeded the stratosphere with ozone. We have done our job.” She courageously puts her head on the block, and the guillotine comes down. Again it stops short and she walks away, a free woman. Then the president of the American Physical Society says: “I don't have any regrets either. We've circled the equator with our newest SSC and have given you the Higgs boson, we've given you light that you can squeeze until it hurts, and we've discovered over 100 theoretical models which should lead to room-temperature superconductors. We haven't given you any real ones because there aren't any—we've tested all the possibilities. But, by the way, while we've been standing here, I've done a back-of-the-envelope calculation and I've found out wha's wrong with this guillotine. If you give me a screwdriver I can fix it.”

Rebound velocity characteristics of wide body tennis rackets with different string tensions

Rebound velocity characteristics of wide body tennis rackets with different string tensions

Measuring the vibrations of a racket handle and the wrist joint in the tennis forehand drive

s-International Society of Biomechanics XIII Congress 1991 719 MEASURING THE VIBRATIONS OF A RACKET HANDLE AND THE WRIST JOINT IN THE TENNIS FOREHAND DRIVE Ryoso Tomosue, Yoshiteru Mutoh, Keiko Yoshinari and Yoshihiko Kawaxoe Department of Sports Sciences, College of Arts and Sciences, University of Tokyo, Komaba 3-8-1, Meguro-ku, Tokyo, JAPAN. The present study was designed to measure the vibrations of a racket handle and the wrist joint simultaneously from the view point of inducing upper extremity injuries. Seven Dunlop tennis rackets with different frame body width, face area, flexibility and string tension were selected. All rackets have the same weight and grip size. A male tournament player stroked flat forehand drives. The amplitude magnitude was defined as the difference between the positive and negative peaks of the vibration immediately following impact. In the case of the center impact, the amplitude magnitudes of the wrist joint were so small as to be a one-tenths of that of the racket handle. The high frequency vibrations were evident only on the racket handle. In the case of the off-center impact, the amplitude magnitudes of the wrist joint and the racket handle showed 1.9-3.1 times and 1.3-1.6 times of those of the center impact, respectively. When comparing these seven rackets, there were no significant differences in their vibration responses for both a racket handle and the wrist joint. LONGITUDINAL STUDY ON SELECTED SPORTS PKRFORMANCE RELATED WITH THE PHYSICAL GROWTH AND DEVELOPMENT IN TWINS. T.Goya, YAmano, T.Hoshikawa and H.Matsui Department of Physical Education Aichi University of Education, Kariya, AICHI 448, JAPAN The purpose of this study was to evaluate the similarity and dlfferentia of the characteristics and selected sport performances (running, throwing and swimming) in MZ and DZ twins. Furthermore a significance of the heritability and trainability in determining the individual variation of those parameters by means of longitudinal design. The data for this experiments of motor patterns were obtained by cinematographic and video taped procedure. Comparison of the differences between MZ and DZ twins were made by intrapair difference (X) . Anthropometric parameters, except body weight, were significant differences between MZ and DZ twins in the series of the growth and development respectively. Aerobic power for physical working capacity might be relied on the difference of the usual physical activities. Kinematic variables in running were related with genetic factors based on the discussion of intrapair difference and motor patterns between MZ and DZ twins. However, Motor patterns and Kinematic variables in throwing and swimming performance seemed to be influenced by a total amount of individual activities and experiences, especially by learning and training. THE DETERMINATION OF THE SUBTALAR PRONATlON AXIS OF ELITE HIGH JUMPERS ATTOUCH-DOWN BEFORE TAKE-OFF: A THREEDIMENSIONAL CINEMATOGRAPHICAL APPROACH Van Gheluwe and E. Deporte Laboratory of Biomechanics, Vrije Universiteit Brussel, BrusselsBelgium Aithou determined a h the orientation and positition of the subtalar pronation axis has been ‘g undantly in literature, it has never been determined during a highly dynamic movement such as high jumping. As force plate data and high speed video pictures recorded during competition, est excessive loads on the lower extermities at take-off, it is assumed that the sug subta ar ? pronation axis during ground contact may shift consrderabiy from the conventlanai orientation andposition. Threedimensional high speed cinematography, at 500 frames a second, was used to reconstruct the movement of the lower leg of elite high jumpers in aotion. The results of this study show pronation axes oriented somewhat differently from what is usually found in literature. This will have to be taken in account when developing biomechanical models in order to evaluate joint forces and moments of the ankle joint.

CAE of Tennis Rackets with Impact Phenomena. Prediction of Racket Response and a View of Restitution in Racket-Ball Impact.

There are a number of unclarified points regarding the impact phenomena and the optimum design of tennis rackets. The present study is based on the idea that the dynamics of a racket consists of the dynamics of a rigid body with an arm swing given at a grip as a boundary condition, an impact between a ball and strings with racket frame as an input force, and the structural vibration of the racket. In this paper, impact force and impact duration are investigated, considering the strong nonlinearity of the restoring force of ball and strings. Furthermore, the coefficient of restitution of the tennis racket is estimated using a personal computer on the basis of the impact phenomena and the experimental modal analysis. In order to predict the contact duration, which has an influence on the racket vibration, a simple impact model has been proposed, i.e., that the contact duration is determined by the natural period of a whole system composed of the mass of the ball, the stiffness of the ball and strings, and the reduced mass of the racket at the impact point on the racket face. The calculated results agree fairly well with the experimental results.

Modal analysis of tennis rackets

The modes of vibration of four tennis rackets are compared: two of the new “wide‐body” rackets, a midsize racket with a graphite composite frame, and an inexpensive midsize racket with an aluminum frame. In all four rackets, the strings vibrate in modes that resemble those of a membrane, while the frames show a variety of bending and torsional modes. The coupling between the string modes and the frame modes is weaker than expected. The enormous popularity of wide‐body rackets is attributed to their greater “power,” resulting from greater frame stiffness. This is especially evident in the higher frequencies of the torsional modes of the frame, although bending modes occur at higher frequencies in the wide‐body rackets as well. The wide‐body rackets in this study were furnished by Pro‐Kennex.

Effects of dynamic features of tennis rackets on muscular load of tennis players

Effects of dynamic features of tennis rackets on muscular load of tennis players

Wrist Pain Associated With 'Fractured' Handle Weights in a Tennis Racket.

In brief: Three tennis players had vague wrist pain when hitting the ball; all three were using the same racket model. Results of physical examination of the three patients were unremarkable, but x-rays of the tennis rackets showed a 'fracture' in the handle weights. Replacement of the racket with an identical new model relieved the symptoms in all the patients.

The retail inventory method: The third major costing system

AbstractAn organization that has but a single product would be a rarity in the United States today. While single‐product firms and tools such as break‐even analysis may have been in vogue at the turn of the century, today jointness pervades the scene. The bank that issues a mortgage to a customer also may have managed his or her checking account or granted a student loan to his or her daughter. The department store that sold a suit one week earlier may have attracted the customer with its furniture, toys, and cosmetics. The hospital whose obstetrical team delivered the baby may have been chosen because its excellent orthopedics department set the husband's broken leg three years prior. The sporting goods manufacturer may sell its golf clubs because of its reknown for skis and tennis rackets. It makes no difference whether it is products or services or departments; all share equipment, time, and reputation. The list goes on forever; jointness is the rule, not the exception.Management can pretend that there is only one product and attempt to isolate its effects, as if it were in a vacuum. However, pretending does not eliminate jointness and the purifying assumption is apt to mislead analysis. So how should jointness be treated?Other than the mathematical programming models of the last forty years, only one model for dealing with jointness has been widely adopted for most of the twentieth century; that model is the retail inventory method. The retail system typically is used by department stores to control inventories that consist of 100,000 or more items.The retail system recognizes costs and prices, inflation and obsolescence, mistakes and successes. It tracks purchases and sales, deals with discounts and transfers, and controls investment while providing an estimate of ending inventory. Fortunately, the retail system, the favorite of the department store and the boutique, could be used in the factory as well as in a variety of service and nonprofit organizations.This article briefly reviews the retail method and then uses linear programming (LP) and postoptimality analysis to modernize the traditional conceptions—to attempt to make a good system even better.Many constraints are studied including overlapping seasons, sales quotas, target inventories, product life cycles, and spatial and monetary limitations, among others. In the process, one comes to appreciate the size of the inventories being controlled, the human and departmental interactions, and the usefulness of the LP‐retail system (“knotty retail” is perhaps an appropriate name) not only to generate cash budget estimates and to manage stock levels, but also to select the most satisfying alterations of managerial policy.The article concludes by discussing further constraints and other types of organizations that might benefit from adapting the retail system.

Strings for tennis rackets and rackets equipped with same: Benichou, A. and Siguier, M. (Societe Anonyme D'Exposifs et de Produits Chimiques & Max Siguier, Paris, France) US Pat 4 530 206 (23 July 1985)

Strings for tennis rackets and rackets equipped with same: Benichou, A. and Siguier, M. (Societe Anonyme D'Exposifs et de Produits Chimiques & Max Siguier, Paris, France) US Pat 4 530 206 (23 July 1985)

硬質ナイロンネットを利用した Shadow Tray の考案

It is a well-known fact that skin injuries after high-energy photon beam radiotherapy are attributed to the secondary electron emitted from acrylic shadow trays. We applied, as a shadow tray material, a high-impact nylon net used generally for tennis rackets, Comparative studies on surface doses in radiotherapy with Linac 10 MV (Toshiba) in conjuction with acrylic trays or the novel nylon net tray were carried out, with the facts being reparted below. In a clinical setting (i.e., source-to-chamber distance 90 cm, tray-to-surface distance 17 cm, field size 15x 15 cm^2), surface doses at a peak depth 25 mm were normalized to the value in the use of conventional trays (5 mm acrylic+10 mm acrylic) respectively in the following tray occasions. a) 5 mm acrylic-high-impact nylon. b) 7 mm lead-acrylic-high-impact nylon. c) hight-impct nylon + high-impact nylon. Normalized data clearly showed improved reduction in the secondary electron of a) 23.6% b) 37.3% c) 42.6% The dramatical reduction (42.6%) in the surface doses thus far obtained by use of the high-impact nylon net tray would greatly benefit clinical radiotherapy.

Spin Imparted to a Tennis Ball during Impact with Conventionally and Diagonally Strung Rackets

Abstract This study compared the amount of spin imparted to a tennis ball during impact with conventionally and diagonally strung tennis rackets. Balls were projected at the rackets at an angle of approximately 45°. The head of each racket was oriented vertically and clamped to eliminate any influence that deformations of the frame would have on the forces transmitted to the ball during impact. Ten multiple-image photographs (five using a relatively slow ball velocity and five using a relatively fast ball velocity) were taken of a ball approaching, striking, and leaving the rackets. For similar pre-impact conditions, it was found that the angular impulse of the contact force applied to the ball (and hence the amount of spin) was almost identical for the two string configurations. Possible explanations of this finding are discussed.

The Design, Development and Manufacture of a New and Unique Tennis Racket

This paper describes how a revolutionary new process was devised for producing top quality tennis rackets from carbon fibre reinforced thermoplastic by a specially developed injection moulding process. The product and process were evolved following an initial study by a multi-discipline team in January 1978 which led to a fully engineered manufacturing process starting production in November 1980. The new racket undercuts the price of competitors' carbon fibre composite rackets in a market sector of growing importance, and the ‘added value’ of the product is significantly higher than that for conventional wooden rackets currently manufactured by the Company. When other comparisons are made with wooden racket manufacture, the new product and process show advantages in nearly every aspect of production efficiency. The new racket and process which are protected by three patents, won a Design Council Award in 1981 and was the winner of the Willis Faber Manufacturing Effectiveness Award organized by the Institution of Mechanical Engineers in May 1982.

Vibration and rebound velocity characteristics of conventional and oversized tennis rackets.

Abstract Stroboscope photography and accelerometry techniques were used to measure rebound velocities of tennis balls from impact locations on the strings and vibration levels at the rotation point on the racket handle for both conventional and oversized tennis rackets. The oversized rackets demonstrated lower vibration levels and higher rebound velocities than their conventional counterparts when balls struck by the racket were compared along a transverse axis drawn perpendicular to the racket shaft and through the geometric center of the strings. These differences were, however, only significantly different (p < .01) at the impact location 6 cm along this axis toward the top edge of the racket. Higher rebound velocities were recorded at all impact points from the oversized rackets along the axis in line with the racket shaft. Significantly lower vibration levels were apparent at locations 4 cm, 6 cm, and 8 cm from the string center away from the racket handle. The lower vibration levels, particularly at the extremes of the racket face, in conjunction with higher rebound velocities, support the concept that this new racket design is of practical benefit to users.

Physics of the tennis racket

Several parameters concerning the performance of tennis rackets are examined both theoretically and experimentally. Information is obtained about the location of the center of percussion, the time a ball spends in contact with the strings, the period of oscillation of a tennis racket, and the coefficient of restitution of a tennis ball. From these data it may be possible to design a racket with improved playing characteristics.

Golf club shafts and Tennis rackets made of Carbon Fiber Reinforced Plastics

Golf club shafts and Tennis rackets made of Carbon Fiber Reinforced Plastics

A new perspective in group art therapy

Previous approaches to group art therapy, and to the more general practice of individual art therapy, have been primarily concerned with the expression of emotional conflict through both the production and discussion of art. The following analysis will present a new approach to group art therapy, utilizing a variety of media within the visual arts. The position to be presented does not negate the importance of a therapeutic approach dedicated to the resolution of conflict and inner tension, but does offer a new and vital dimension to the group art experience. More than three years of research involving hundreds of group sessions with severely disturbed and chronic mental patients, young children (including children from different cultures) in a variety of educational situations, graduate students and university teachers, psychiatric staff, and many other adult groups in our society have supported the principles to be presented. The new position put forth by our work is based upon the conviction that a one-sided involvement with the often vague and confusing unconscious features of the art experience fails to maximize the therapeutic potential of an analysis of objective pictorial dynamics. We emphasize the conscious and critical thinking nature of artisitc problem-solving and work toward a sharpening of the visual sense. This process is greatly facilitated by the group experience, which offers a rich variety of artistic stimuli and provides for interpersonal sharing and communication. The organic and personal nature of artistic productions has stimulated serious and orderly reflection in the lives pf many individuals where other more abstract and sometimes impersonal media have proven te be ineffective. The group process is enhanced by having something definite, concrete, and personal to relate to. For example, seventy-five year old Max, who strongly resisted the pressure of his group to involve him in their discussion, finally broke months of silence when a young woman looking at his picture asked: “What are those tennis rackets doing in your picture?” Max shook his head, smiled and spoke right up, informing her that they were “trees” and not “tennis rackets.” Max is one of the many people who have been moved toward verbalization through art. The example cited above also demonstrates how art therapy does not always have to immerse itself in psychopathology and interpretation to be effective. We have discovered that an approach to art which does not deny the expression of pain and conflict but which primarily concerns itself with the positive significance of artistic expression promotes a high degree of trust in the group experience. In the early stages of the group this sense of security is conveyed by the attitudes of the group leaders, who act as facilitators of the group process and who stimulate group members to think, act, and make decisions as individuals. Because of the critical perceptual difficulties of many psychiatric patients, we emphasize the importance of distinguishing between what is objectively present in perception and the subjective feelings of the viewer. In group discussions we approach the

Contact dermatitis caused by bamboo.

Recently I was called to investigate an outbreak of dermatitis in a factory that manufactured tennis rackets made of bamboo. The bamboo used was in long strips, devoid of bark and hair, and prior to being molded into shape it was put through a sanding process. A check of dermatological literature revealed no reports of any dermatitis due to bamboo. It is felt, therefore, that the following cases are worthy of report. REPORT OF CASES Case 1.— R. M., aged 50, had been a bamboo sander for the past 30 years. He was first seen by me on April 1, 1950, and presented an erythematovesicular, oozing and crusted dermatitis involving the dorsal and palmar aspect of both hands, the volar and ulnar surfaces of both forearms and the neck and face, accompanied with severe itching, of two weeks' duration. He gave no history of previous skin disease. He related that recently