Trial setup for evaluating the effect of hand gripping on the vibrational behaviour of a tennis racquet

Playing tennis exposes the human body to repeated impacts of the ball with the strings of the racquet, producing shock waves to travel down the racquet and propagating through the musculoskeletal system. The tennis elbow, also known as lateral epicondylitis, affects 40% to 50% of recreational players. The transfer of vibrations to the arm by the hand, because of the impact between the racquet and the ball, is one cause of developing tennis elbow. Many studies in literature investigated the factors that contribute to the development of this condition; however, few studies proposed techniques and solutions to prevent it from occurring. The aim of this project is to realize a trial setup for evaluating the effect of hand gripping on the vibrational behavior of a tennis racquet. In this way it would be possible to test objectively the biodynamical characteristics of tennis racquets under standardized but biomechanically realistic conditions. Specifically, the target is developing a tennis racquet mount that simulates the human hand in terms of vibrational behavior during a forehand stroke with a semi-western grip. The study is focused on obtaining the same value of first bending mode’s frequency and damping coefficient for both the tennis racquet mount and the human hand. For the realization of the experimental setup were made two hand surrogates and a suspension structure. Several experiments were carried out to test both the surrogate and the mount's reliability; in particular, the dynamics of the freely suspended racquet, the suspended racquet gripped only by the hand surrogate, the racquet gripped by the hand surrogate and suspended with the mount, and finally the racquet gripped by a real human hand were analyzed. The results obtained showed that the implemented system approximates tennis player hand’s vibrational behaviour in frequency terms, under the specific boundary conditions chosen and applied in the experimental tests. A peak frequency value of 135±1 Hz was obtained with the prototype developed and 134±2 Hz with the human hand. Damping coefficients of 30,8±3,3 33,4±1,2 34,9±1,1 (%) were also achieved respectively with the loose, medium and tight grip conditions tested with the second hand-surrogate. Based on the data acquired, it is possible to conclude that the trial setup designed provides realistic findings that are also in line with the literature. The limits of the project are defined by the imposed experimental conditions, which were set to allow for valid comparison of the outcomes of all the experimental studies. Future advances would mostly focus on modifying the boundary conditions, such as testing different racquets, hitting points, and applying higher ball incoming velocity. Furthermore, the actual hand surrogate could be enhanced to evaluate impact forces also in the wrist and forearm to explore their effects and the relationship between them and the most common upper limb injuries among tennis players.