Hypothesis
When a tennis ball hits a racquet, mechanical vibrations of the racquet are transmitted along the racquet frame to the hand and forearm of the player. These vibrations can cause discomfort and have been hypothesized to cause fatigue and negatively impact performance in tennis players.
A study by the Wilson Sporting Goods Company in conjunction with the University of Minnesota School of Kinesiology & Center for Clinical Movement Science set out to observe the negative effect of vibrations on tennis players and determine if there was a decline in performance over the duration of a match, as well as provide an option that would help reduce vibrations and improve performance.
Two of the same model tennis racquets provided by Wilson were used in the study. They looked identical and had the same mass, center of mass, stiffness, head area and were strung with the same string pattern, type and tension. To the test subjects, the racquets were identical. One racquet, however, had Countervail® composite material integrated into the frame. The inclusion of Countervail material was hypothesized to maximize the dissipation of mechanical energy throughout the tennis racquets, contributing to reaching the goal of lessened fatigue and improved performance.
Testing
Nineteen right-handed tennis players from the University of Minnesota participated in the study. Nine women and 10 men with an average age of 21 years were among the participants – all had trained regularly throughout the year, and none reported any musculoskeletal or neurological impairment prior to the study that might impact the results. In order to gather data, accelerometers were secured to the shaft of the racquet, above the handle grip tape and on the dorsal side of the forearm, in order to measure the vibrations at impact.
Experimental Modal Analysis was used to extract peak acceleration and acceleration signal energy of both racquets in order to test the racquets while they were not being handled by a player. An impact hammer contacted the racquet at the same impact point five times on each racquet in order to obtain a baseline of comparison prior to human testing.
In order to test the performance over a sustained period, subjects participated in three sets of serves and forehands, with a 1-minute break in between. The first set consisted of 15 serves and 45 forehands, and the second set consisted of 30 serves and 90 forehands. The final set did not have a set duration, with 45 serves and continued forehands until the participant felt they were nearing exhaustion. After every 15 hits, participants rated their perceived level of exertion on the Borg Rating of Perceived Exertion (RPE), which ranges from 6 (no exertion) to 20 (maximal exertion).
Results
Even prior to the racquets being used by the tennis players, the effect of vibration damping was visible. The acceleration signal energy of the Countervail-integrated racquet was 74 percent lower compared to the racquet without Countervail.
Vibrations to the forearm and hand were markedly reduced in the tennis racquet integrated with Countervail. The mean peak acceleration was reduced by 45.2 percent at the hand and 95.6 percent at the forearm as compared to the normal Wilson tennis racquet. Furthermore, the level of fatigue of tennis players improved using the Countervail-integrated racquets. At near-exhaustion, players using the Countervail racquets placed 25 percent of their returns in the target area, compared to 17.6 percent with the normal racquet.
The results of this study provided conclusive evidence that the tennis racquets integrated with Countervail’s vibration-damping technology reduced or delayed signs of muscular fatigue after prolonged play. With players experiencing less racquet vibration with the same feel as the normal racquet, less fatigue and greater control over shots when nearing exhaustion, the racquets with Countervail’s vibration-damping technology successfully proved the initial hypothesis. Since the experiment concluded, Wilson has introduced seven Countervail-integrated tennis racquets into their lineup. To read the full report, click here.
Want to learn more about Countervail Products LLC’s vibration-damping technology? Contact a Countervail engineer today to discuss integrating Countervail in your sporting goods application.
1. I-LingYeh, et. Al, “Vibration-Damping technology in tennis racquets: Effects on vibration transfer to the arm, muscle fatigue and tennis performance”, Sports Medicine and Health Science
Volume 1, Issue 1, December 2019, Pages 49-58.