The Effect of Tennis Racket Stiffness and String Tension on Ball Velocity after Impact

Abstract

This study was undertaken to determine influences of string tension and longitudinal flexibility on ball velocity after impact. Three rackets, each of three types classed as Stiff, Average, and Flexible by their manufacturers, were strung with nylon at 40-, 50-, and 60-pound string tensions and subjected to 16 ball/racket impacts. Impact was photographed through a rotating slit disc. Racket head deflection and ball displacement were measured using a Vanguard Analyzer and Digitizer system. Differences in racket head deflection and ball velocity ratio between racket types were investigated using an analysis of variance and Newman-Keuls' post hoc test. Differences in racket head displacement and ball velocity ratio caused by changes in string tension were not independent of differences in longitudinal flexibility. Average flexibility rackets gave significantly less head displacement than Flexible rackets at string tensions of 50 and 60 pounds. Average rackets at 60-pound tension gave significantly less head displacement than in all other test conditions. Stiff, Average, and Flexible rackets behaved differently under dynamic and static conditions. Average and Flexible rackets at 50-pound tension gave significantly higher ball velocity ratios than at other tensions.