BIOMECHANICAL SIMILARITIES AND DIFFERENCES OF A. AGASSI'S
FIRST AND SECOND SERVES
A. VOROBIEV, G. ARIEL, D. DENT
International Center for Biomechanical Research
INTRODUCTION
The purpose of this study was to perform three-dimensional analysis of the instrumentally recorded elements of Andre Agassi's (1992 Wimbeldon and Davis Cup champion) serving technique during competition. Kinematic parameters of his first and second serves were compared.
METHODS AND PROCEDURES
Data were collected during the match A. Agassi vs. B. Gilbert (November 24, 1992). A video based analysis system was used to analyze the data provided by two sVHS (60 Hz) back and right side view camcorders. Three dimensional DLT transformation was performed using preliminary filmed 8 m3 calibration cube. Eighteen body, one ball, and four racquet points were digitized over the sequence of the 85 frames for each view and for each serve.
Four successful first and second into the deuce court serves were selected for the analysis. Spatial linear kinematic characteristics of the digitized points and angular parameters of the defined segments were obtained and analyzed.
RESULTS AND DISCUSSION
The average speed of the ball for the first serve was 45.8�2.2m/s and angled close to the sideline. The second serve was hit with pronounced topspin and achieved a ball speed of 37.9�2.4m/s. J
Kinematic characteristics of the CG in the preparation phase reflects direction, velocity and rotation of the ball. The first serve's CG maximum speed was 1.89�0.1Orals. Angle of the horizontal velocity at the moment of impact was
17�4 degrees. The characteristics of the second serve were 1.71�0.09m/s and 10� 5 degrees. However, the vertical component of CG velocity of the second serve was 12% higher than the first which most likely provided additional ball rotation. The ball positioning relative to the CG at the moment of impact for the first serve was 0.13�0.02m forward and 0.12�0.04m laterally. The second serve had no
significant forward shift between the ball and CG. Lateral shift was 0.36�0.04m. The height of the ball impact was relatively the same for both serves.
Analysis of body segment movements during the first serve gives the following results: high speed right knee extension, hip and shoulder rotation provides pronounced forward body motion. In the second serve extension of the
left knee was dominant with less influence by the hip and shoulder rotation, but with more notable lateral trunk action. No significant differences were found between right arm and racquet's relative movements during the first and the second serves. In both cases maximum angular velocities of the elbow extension and a racquet swing were 1185�110 deg/s and 3240�180 deg/sec respectively with the same structure of the velocity changes.
CONCLUSIONS
It was found that in order to increase consistency of the second serve, Agassi while keeping the relative motion of his arm consistent from serve to serve, makes changes in his vertical and lateral position, "and the forward motion of his body which causes changes in the velocity and rotation of the ball. Since the torso and leg muscles are larger than the arm muscles, they are stronger and more stable, thus providing consistency in changes of motion patterns for the second serve.
