Kinetic Chain:

Figure 1. The movement pattern of an elite tennis server (Image credit: Roetert et al.)

The kinetic chain is a series of linked segments of a body that move together (Blazevich, 2010). Two different forms of this chain include the push-like pattern and the throw-like pattern. At an elite level, the tennis serve is accomplished using the throw-like pattern, meaning that it is a sequential movement pattern starting at the feet, moving up through the trunk, and all the way out through the hand and racquet. According to Kibler (2009), 51% of kinetic energy is produced by the trunk and legs, 13% by the shoulder, 21% by the elbow and 15% by the wrist.

The tennis serve can be broken down into three phases; preparation, acceleration and the follow-through. In the preparation phase, which includes the ball toss and ends at the full shoulder external rotation, potential energy is stored to be used as kinetic energy in the acceleration phase (Kovacs & Ellenbecker, 2011).  A great deal of energy is obtained through the flexion of the knee (shown in images B-C in Figure 1) as it produces a ground-reaction force (Roetert et al, 2009). This means that the ground gives off an opposite force to that of the downward force being placed on it by the foot, relevant to Newton’s third law of motion.  In Figure 1 (images C-E) we can also see a hip and trunk rotation, which is the next sequential part of the kinetic chain.

The acceleration phase begins as the kinetic energy moves up into the shoulder and arm due to the hip and trunk rotation (Kovacs & Ellenbecker, 2011).  At this stage of the movement pattern, the shoulder has rotated so the elbow has undergone flexion behind the back, as can be seen in Figure 2. The arm then starts to generate torque as it is swung back around to make contact with the ball. The ball is contacted when the elbow is almost at maximum extension, with the forearm facing toward the ground. This internal shoulder rotation movement is evident in images D-F in Figure 1, which is a large contributor to the high speed of the racquet head at the point at which contact is made with the ball (Roetert et al, 2009).

Figure 2. The acceleration phase of the tennis serve (Image credit: Abrams et al.)

The last phase of the movement pattern is the follow through. During this phase, the body undergoes deceleration and finishing the shot in order to prepare themselves to play the next shot returned by their opponent. This aspect of the serve is the most violent on the body, where internal shoulder rotation and forearm pronation continues right through past the trunk in order to ensure the ball is going in the right direction (Kovacs & Ellenbecker, 2011). It is here where the muscles around the shoulder and arm begin to decelerate. The abdomen’s internal oblique muscle, on the side of the players opposing hand, is very active in this part of the shot, as it has to maintain stability in the trunk and help pull it back from an unbalanced position back to a balanced one (Kovacs & Ellenbecker, 2011).

The last part of the movement pattern is where the lower body lands back on the ground. When the front foot contacts the ground it creates eccentric and horizontal braking forces to stabilise the body (Bahamonde & Knudson, 2001). Due to the players momentum behind the ball and sudden stopping, the player will lean right forward and over the front foot creating a shift in the centre of mass (Bahamonde & Knudson, 2001). To counteract this, the back leg is kicked out behind to maintain balance, which can be seen in both image F in Figure 1, and more clearly in Figure 3 below. This allows the player to then come back together in the upright position without falling over, and get ready to return the next shot.

Figure 3. The athlete stabilising his body using horizontal breaking forces in his front leg, and swinging his back leg behind to maintain balance. (Image credit: Kovacs & Ellenbecker)