Dimensions of the functional degrees of freedom of the first serve in tennis.

We examined the influence of court side and target location of the ball on the coordination and control of the tennis serve. Five male and five female experienced players performed 10 'first-serves' to centre and wide targets. 3D kinematics of the service were analysed from two frames of reference: joint position (v) and joint angle (ω) with emphasis on the qualitative aspects of movement coordination. Principal component analysis (PCA) showed in all service location conditions the first two components accounted for ~80% of the total variance with the external frame of reference (elbow and shoulder v), and internal frame of reference (ω: left and right hip) contributing most to component 1 (~60%). Arm (ω: shoulder, elbow, wrist) contributed (~20%) to component 2. Serving toward the court T centre led to more variables involved in the organization of the motion. Peak mean racket head resultant velocity was similar with each serving condition, but higher in males than females. The PCA showed that the number of components (Functional Dimensions) was less than the number of joint space physical DFs. There was quantitative variation in individual kinematic variables within- and between- players but a common qualitative kinematic structure to the coordination solution.