The Effect Of Tennis Racquet Flexibility On Ball Velocity After Impact

Abstract

Recent claims by tennis racquet manufacturers have stated that stiffer racquets produce greater power which, in tennis terminology, is considered synonymous with rebound velocity. Results from previous studies have not shown a consistent relationship between racquet flexibility and rebound velocity (Baker and Wilson, 1978; Elliot, 1982). However, in a study based on mathematical modeling, Brody (1979) stated that a stiffer racquet should absorb less energy and produce a higher rebound velocity. Recent changes in tennis racquet design have allowed for greater variability in racquet stiffness. Therefore, the purpose of this investigation was to test the effect of racquet flexibility on ball velocity after impact. A standardized static flexibility test was performed on 12 racquets in order to classify them as stiff, average or flexible. The racquets, four of each classification, were strung with nylon at 60 pounds of tension, and subjected to eight ball to racquet impacts at an average inbound velocity of 33 ± 4 meters per second. Ball velocity before and after impact was calculated with the use of multiple exposure photographs created by a stroboscopic light set at 150 flashes per second. The results indicated mean ball velocity ratios (inbound velocity/ outbound velocity) of 0.448 ± .02 for the stiff racquets, 0.407 + .01 for the .average racquets and 0.374 ± .02 for the flexible racquets. A one-way analysis of variance was used to test for significant differences between groups. Results from the ANOVA showed that differences were present, and a Tukey post hoc test determined that significant differences existed between the mean values of all three groups (p<.017). A high correlation (r =0.92) between racquet stiffness and ball velocity ratio was calculated with the use of a simple regression analysis. These results indicated that stiffer racquets produced higher rebound velocity, and thus may be capable of producing more power. This infonnation may be useful for tennis players desiring more or less potential power from their racquet. The results from this study contradict earlier findings, but support the claims by tennis racquet manufacturers that stiffer racquets are more powerful than flexible racquets. References Baker, J., & Wilson, B. (1978). The effect of tennis racquet stiffness and string tension on ball velocity after impact. Res. Ouarterly, 49, 255-259. Brody, H. (1979). Physics of the tennis racquet. American Journal of Physics, 47, 482-487. Elliot, B. (1982). The influence of tennis racquet flexibility and string tension on .rebound velocity following a dynamic impact. Res. Ouarterly for Exercise and Sport, 53, 608-615.