Vibration absorption in the tennis grip and the effects on racquet dynamics
Creators: name: Savage, Nicholas
Publisher: name: RMIT University
Year: 2024

description: The modern game of tennis has changed in recent years as a result of lightweight, stiffer racquets. The evolution of the tennis racquet, with respect to both design and materials, has increased the speed of the game but also the levels of stress placed on the player's bodies. Many believe that injuries such as lateral epicondylitis (tennis elbow) are caused and aggravated by the absorption of racquet energy by the player, in the form of shock and vibration. This thesis presents an experimental investigation into the absorption of racquet vibration to the player's hand and forearm.<br><br>Quantification of the tennis grip has been achieved in this research using different experimental techniques to analyse different aspects of the tennis grip. Grip pressure distribution profiles during impact have been established using both pressure sensitive film and real-time data acquisition methods. Quantification of grip tightness during impact, together with gripping times, has also been quantified using a strain gauge cantilever system manufactured specifically for this research. The experimental data acquired in this research has provided the base for grip pressure distribution profiles to be established for three stroke types (e.g. Forehand, service and the problematic backhand). The profiles depict the distribution of pressure in the tennis grip in relation to the ball impact, in the time domain. Based on these grip profiles, the research hypothesises hand movements in an attempt to establish muscle contractions (and moreover locations of vibration absorption) specific to stroke types. <br><br>The research investigates the absorption of racquet vibrations by the player's hand in the time domain. Filtering of accelerometer data allows for the isolation of specific frequencies of interest (i.e. below 200Hz). Logarithmic decrement of racquet vibration has been calculated and related to the grip pressure distributions in the time domain, and the relationship between grip pressure and vibration damping has been modelled. The correlation between grip pressure and the logarithmic decrement has been show to be significant (p less than 0.005) and non-linear. The relationship between the tennis grip and the damping of racquet vibrations has been found to be dependant on both grip pressure and the proximity of grip pressure application in proximity to the handle node. Grip pressure applied to the racquet close to the handle node has a greater damping effect than a similar pressure further away. <br><br>In addition to these key research findings, the effectiveness of a piezoelectric racquet damping system is also investigated. A comprehensive modal analysis of two tennis racquets is given with further ball impact tests. The ball impact tests showed that the damping system has a 28% difference in racquet vibrations during freely suspended grip conditions. However, under hand-held grip conditions the inclusion of grip damping into the system provides a much greater damping entity (880% greater). Therefore, the effect of the piezoelectric system was deemed to be negligible. <br>