The application of advanced engineering to tennis racket design has influenced the nature of the sport. As a result, the International Tennis Federation has established rules to limit performance, with the aim of protecting the nature of the game. This paper illustrates how changes to the racket affect the player-racket system. The review integrates engineering and biomechanical issues related to tennis racket performance, covering the biomechanical characteristics of tennis strokes, tennis racket performance, the effect of racket parameters on ball rebound and biomechanical interactions. Racket properties influence the rebound of the ball. Ball rebound speed increases with frame stiffness and as string tension decreases. Reducing inter-string contacting forces increases rebound topspin. Historical trends and predictive modelling indicate swingweights of around 0.030–0.035 kg/m2 are best for high ball speed and accuracy. To fully understand the effect of their design changes, engineers should use impact conditions in their experiments, or models, which reflect those of actual tennis strokes. Sports engineers, therefore, benefit from working closely with biomechanists to ensure realistic impact conditions. 相似文献
Objective: To analyze the association between attitudes of filial responsibility and adult child caregivers’ behaviors in the Southern Region of Brazil.
Methods: Cross-sectional study with 100 child caregivers of older adults. The data were collected through an interview using the protocol of filial responsibility adapted and validated to Brazilian Portuguese. Filial Expectation and Filial Piety scales evaluated the attitudes of filial responsibility. Caring behaviors assessed were: instrumental support, emotional, financial support, and companionship. The variables that presented p< .20 value in the bivariate analysis were inserted into a multivariate Poisson regression model.
Results: Financial and emotional support behaviors were significantly associated with filial piety (p = .050 and p = .001, respectively) and filial expectation (p = .013 and p = .023, respectively). Providing companionship was associated with filial piety (p = .015).
Conclusion: Attitudes of filial responsibility are associated with some but not all caregiving behaviors. Brazilians caring for older parents show more similarities to Chinese than to Canadian caregivers. Furthermore, filial responsibility and caregiving behaviors are strongly affected by Brazilian social and cultural norms. Reasons are discussed. 相似文献
Memorial University has been active in the use of educational media since its creation, and operates a public channel, initially broadcast through CBC but now on cable distribution. The author discusses the changes that have occurred over the past few years in the role of television there and describes the interactive element called PLA YBA CK, through which viewers can now access any of 1000 programmes by a telephone call to the control room. The reader is invited to consider the changes in philosophy such developments inevitably entail. 相似文献
Many aspects of human movements in sport can be readily understood by Newtonian rigid-body mechanics. Many of these laws and biomechanical principles, however, are counterintuitive to a lot of people. There are also several problems in the application of biomechanics to sports, so the application of biomechanics in the qualitative analysis of sport skills by many coaches has been limited. Biomechanics scholars have long been interested in developing principles that facilitate the qualitative application of biomechanics to improve movement performance and reduce the risk of injury. This paper summarizes the major North American efforts to establish a set of general biomechanical principles of movement, and illustrates how principles can be used to improve the application of biomechanics in the qualitative analysis of sport technique. A coach helping a player with a tennis serve is presented as an example. The standardization of terminology for biomechanical principles is proposed as an important first step in improving the application ofbiomechanics in sport. There is also a need for international cooperation and research on the effectiveness of applying biomechanical principles in the coaching of sport techniques. 相似文献
A deterministic model is a modeling paradigm that determines the relationships between a movement outcome measure and the biomechanical factors that produce such a measure. This review provides an overview of the use of deterministic models in biomechanics research, a historical summary of this research, and an analysis of the advantages and disadvantages of using deterministic models. The deterministic model approach has been utilized in technique analysis over the last three decades, especially in swimming, athletics field events, and gymnastics. In addition to their applications in sports and exercise biomechanics, deterministic models have been applied successfully in research on selected motor skills. The advantage of the deterministic model approach is that it helps to avoid selecting performance or injury variables arbitrarily and to provide the necessary theoretical basis for examining the relative importance of various factors that influence the outcome of a movement task. Several disadvantages of deterministic models, such as the use of subjective measures for the performance outcome, were discussed. It is recommended that exercise and sports biomechanics scholars should consider using deterministic models to help identify meaningful dependent variables in their studies. 相似文献