Serve has such a big impact in today’s game of tennis. In the time when the most of the points, no matter the surface, are ended by the first four shots, serve has even more important role. When we talk about serve, most the players think about the huge, powerful serves but besides the power the other important aspect of the serve is the tactical placement. For the player to have a constant serve with the power and placement control while minimizing the chance of the injury, understanding of the it’s biomechanics have the crucial importance.
SERVE KINETIC CHAIN
In a dynamic motion such as the serve, the kinetic chain has an evident importance as power and acceleration are required to hit the ball. Body segments must be coordinated and synchronized in such a way that a highest racquet speed is generated at the impact point. For the tennis player to perform the serve mechanic in the most efficient way, different body segments are being used at different points of time, working together from the lower to upper body.
In order to produce the efficient serve, a tennis player must be able to generate power from the lower limbs (leg drive) and transfer it finally to the wrist and the racquet using all possible body segments in a very coordinated and rhythmic movement sequence – kinetic chain.
The leg drive generates approximately 51% of the kinetic energy making it the most important mechanism to generate force. It has been proved that professional players can generate ground reaction forces in the vertical direction up to two times their body weight. The main purpose of an efficient leg drive is to enable the efficient utilization of trunk and upper body rotation to position the hitting arm in maximal external rotation and in this way put less pressure to the shoulder, which can prevent injuries. Poor leg drive on the other hand, with poor knee flexion, place higher loads to the shoulder and elbow. Effective leg drive increases the range of motion of the racket, placing it behind and away from the back enabling players to generate higher racket speeds.
There are two main categories of kinetic chain patterns in a serve: push-like and throw-like.
A push-like kinetic chain pattern is when a player is extending all joints of their kinetic chain at the same time in a same direction (jumping motion). Push-like pattern occurs during the acceleration phase of the serve, where the server’s feet, ankles, calves, knees, and hips push against the ground and extend upwards simultaneously in a single movement, so the server is able to leave the ground. Push pattern is using the ground force reaction which is the result of the server’s toes pressing against the ground.
Throw-like patterns refer to the joints of the kinetic chain extending sequentially, one after another (throwing motion). This throw like motion of the wrist snapping at the impact point contributes at around 40% of the power of the serve. During the acceleration phase, the leg extension leads to the server’s racquet being drawn down behind their back; in other words, creating an opposite reaction force which is a principle of Newton’s third law. The sequence following in the serve motion acceleration phase is that the shoulder begins to extend while the elbow is still flexing. From there with the hip and shoulder rotation of the dominant, hitting side, towards the ball, with the internal shoulder rotation, the arm is following the rotation forward to the impact point from where the relaxed wrist can perform the powerful snapping action.
Next blog: Significance of the leg drive in the efficiency of the serve motion