The Effect of Tennis Ball Pressure on Coefficient of Restitution and Force on Hand

Abstract

Wrist injury is prevalent among tennis players. While it is well known that switching the brands of tennis balls can greatly increase the risk of injury, this study hypothesized that changes in ball pressure, measured by the force on hand (FOH), could be another factor contributing to wrist injuries. The use of a vibration dampener was also investigated to determine if the device could provide any injury prevention benefits. A mechanics model of the racquet-hand system was utilized to derive the force on hand equation, and the relationship between the force on hand and the coefficient of restitution (COR) was established to facilitate data analysis. The study employed a camera system to capture ball-racquet collisions and developed a Python vision tracking program using OpenCV to determine balls’ initial and final velocities and calculate the COR and FOH under four testing conditions. Results showed that, under the same constraint—whether with or without a vibration dampener—new balls exhibited a statistically significantly higher COR and FOH compared to dead balls when colliding with a racquet, which implies that the gradual decrease in ball pressure during a match could lead to notable changes in force on hand, potentially increasing the risk of wrist injury. Furthermore, statistical analysis confirmed that incorporating a vibration dampener not only decreased the force on hand irrespective of ball pressure but also reduced the variation resulting from the difference in FOH caused by varying ball pressure, thereby effectively mitigating the risk of wrist injury.