Two of the most frequently performed vaults in the 1988 Olympic Games in Seoul were selected for 3-D cine-photogrammetry analysis: the Yurchenko layout with full twist and the Yurchenko layout. The performances included 20 vaults with the highest performance scores: 10 Yurchenko layout with Ml twist (YLF) and 10 Yurchenko layout (YL) vaults, which were performed in the women’s team optional competitions. The YLF group earned higher performance scores than the YL group. Average vaulting times were similar for the groups, but the YLF group showed shorter board and horse contact times and longer postflight times. The projectile motion variables were critical for better performance in the YLF group. Higher vertical velocity at horse takeoff was achieved mainly by minimizing its (Vv) loss during horse contact. The YL group showed the importance of angular momentum for better performance, with the normalized angular momentum during postflight being the critical variable for the YL vault.
Young-Hoo Kwon, Virginia L. Fortney and In-Sik Shin
Jack L. Groppel, In-Sik Shin, Julie Spotts and Barbara Hill
Much study has been done to examine the various aspects of tennis racket performance including racket materials, shape, balance, and flexibility, but recently the string in the frame has come to interest scientists. The purpose of this investigation was to determine the effects of varying string tension patterns on the mechanical behavior of racket, string, and ball during and immediately after impact. Two separate experiments were conducted; one examined 12 rackets strung differently with a string lock system by filming the impacts at 3,500 frames per second, and the other quantitatively evaluated the forehand drive results of a skilled player who experimented with the rackets. Differences were found in the various impacts examined, and these differences were attributed to the various characteristics of the string, racket, and ball. In addition, larger coefficients of restitution than those found in previous literature were also calculated.
Jack L. Groppel, In-Sik Shin, Jo Ann Thomas and Gregory J. Welk
This study explored the effects of string type and tension on various factors involved with tennis ball–racquet impact in midsized and oversized racquets. String and racquet material, racquet flexibility, and grip firmness were held constant for each test condition. The dependent variables included postimpact and preimpact ball velocity ratio, racquet head displacement, maximum ball compression, and ball contact duration. It was found that racquet size and string material have varying effects on impact. Although changes in string tension do affect the impact, it is not in a linear fashion. Various string tensions change a racquet's flexibility, thus affecting ball velocity and other factors associated with impact. The results of this study demonstrate the complexity of string and frame interaction.