• R. Bahamonde


INTRODUCTION Joint power calculations not only are related to muscle force but also provide information on the changes in muscle length and the type of load produced (eccentriclconcentric) (Andrews, 1983; ~inte;, 1990). It was the aim of this study to compute the joint power developed at the wrist, elbow, and shoulder joints during the performance of flat and slice tennis serves. METHODS Five male, right-handed collegiate tennis players were filmed using the DLT method of 3D cinematography. Film analysis procedures and quintic spline functions were used to calculate and to smooth the 3D coordinates of the landmarks, respectively. The following events were defined: ball toss (BAT); maximal elbow flexion (MEF); racket lowest point (RLP), start of forward swing; maximum external rotation (MER); and impact (IMP). Rigid body kinematics and the inverse dynamics approach were used to calculate the resultant torque and force at each joint (Bahamonde, 1994). Joint power (P,) was calculated as the product of the components of the resultant joint torque (T,) and the joint angular velocity (a~()W inter, 1990). RESULTS Table 1. Average Joint Power (Watts) Values for the Flat and Slice Serves CONCLUSIONS Large eccentric loads (pre-stretching) were placed on the internal rotator muscles during the late portion of the backswing and the early forward swing; changing into concentric loads prior to IMP. Elbow loads (extension and pronation) were concentric throughout the forward swing. Wrist concentric (flexion and ulnar deviation) loads increased in magnitude near impact (MERAMP). In general, the magnitude of the joint power values were larger for the flat serves than for the slice serves. The joint power needed to accelerate the racket was the result of shoulder internal rotation, elbow extension and pronation, and wrist flexion and ulnar deviation. REFERENCES Bahamonde R. (1994) Biomechanical Analysis of the Serving Arm During the Performance of Flat and Slice Tennis Serves. Doctoral Dissertation, Indiana University. Andrews, J. (1983) Biomechanical Measures of Muscular Effort. Med. Sci. Sport. Exer., 15(3),199-207. Winter, D.A. (1990) Biomechanics and Motor Control of Human Movement. Wiley & Sons, New York.