Figure 1: Kick serve technique showing all sequences throughout the entire skill. (Flickr, 2012).

Introduction:

The serve in Tennis has become a hot topic of late due to the varying styles used and the impact it has on overall performance. Due to the serve being one of the most important strokes in tennis it has provided significant biomechanical interest (Reid, Whiteside, Gilbin & Elliott, 2013) to determine the most effective technique. The serve plays a pre-eminent role in player development and for this reason a powerful and accurate serve is a priority for most players (Reid, et al., 2013). The serve is an attacking phase where the aim is to hit the ball into the opposition’s service area, and to make it difficult for the opponent to return the ball. There are four phases of the tennis serve; preparation, windup and ball release, acceleration and the follow through, and each stage is a direct result of muscle activation and technical adjustments made from the previous stage (Kovacs & Ellenbecker, 2011). Each phase of the tennis serve requires biomechanics to determine which principles optimise the speed and accuracy of the serve in order to create an efficient performance.

This stroke in tennis is a sequence of motions that is commonly referred to as the ‘kinetic chain’, where the ‘chain’ begins with lower limb actions and is followed by rotations of the trunk and the upper limbs (Martin, Bideau, Bideau, Nicolas, Delamarche & Kulpa, 2014). The kinetic chain permits the summation, generation and the transfer of mechanical energy to generate a high ball velocity (Martin, et al., 2014). The throw-like pattern of the kinetic chain is closely related to the tennis serve, as the joints of the kinetic chain extend in a sequence rather than at the same time, as can be seen in Figure 2 below. In the serve much of the force production begins in the legs and hips and continues to the shoulder where it extends, while the elbow and wrist is still flexing (Blazevich, 2010).

Figure 2: Kinetic Chain. This figure shows the kinetic chain where the lower limbs are predominately used early in the serve sequence, and how the body movements become reliant on the upper body as the sequence progresses. The kinetic chain is extremely involved in the tennis serve as the skill movement occurs one after the other rather than at the same time. (GPP Tennis, 2008).

Preparation phase:

During the preparation phase of the Tennis serve, there are minimal biomechanical principles that can be applied. This is because it is a phase where the player is preparing the shot mentally in order to perform an accurate serve. In the preparation phase, the server will have their non-preferred foot up to the line, with the ball in their non-preferred hand and the racquet in their preferred hand. As can be seen in figure 3 below, the non preferred foot should be lined up diagonally across the court with the preferred foot parallel to the base line, which provides good base support and act as a guide for where the ball from the serve is intended to go. Muscular activation during this stage is low, because there is no demand for movement. The overall goal of the preparation stage is to align the body to utilise the ground for force and power generation (Kovacs & Ellenbecker, 2011) for the upcoming stages.

Figure 3: This image shows the athlete at the beginning of the preparation phase, as he is mentally preparing for his serve. As can be seen in the figure above, the athlete has his non-preferred foot up to the line, with the ball in his non-preferred hand and his racquet is in his preferred hand. This stance provides excellent base support for the athlete. (Kovacs & Ellenbecker, 2011).

Ball release and wind up:

The wind up phase begins at the start of motion and ends with the ball release from the non-dominant hand to initiate the ball toss (Abrams, Sheets, Andriacchi & Safran, 2011).

This phase of the tennis serve occurs when the ball is released above the head from the nondominant hand, but in control so it can be easily accessed by the racquet. The ball release should be out slightly lateral to the overhead position of the server (Kovacs & Ellenbecker, 2011), where the racquet should hit the ball at approximately 100 degrees of the overall arm abduction (Kovacs & Ellenbecker, 2011). During the ball release phase, the player should prepare for loading with the ‘foot-up’ technique (Kovacs & Ellenbecker, 2011), which will allow for a greater vertical height. To gain a better understanding of the stance at this stage, figure 4 below shows the foot-up technique and the full arm extension.

When loading, the ground reaction forces from bending the knees result in an off-centre angular impulse (Kovacs & Ellenbecker, 2011) which elevates the arm holding the racquet and lowers the opposite side of the body. This action produces a shoulder over-shoulder rotation as the server explosively moves the arm toward the position of ball contact (Kovacs & Ellenbecker, 2011). These movements require the principle of angular momentum from the lower limbs to the upper limbs (Kovacs & Ellenbecker, 2011), ultimately allowing for greater racquet height.

During this phase angular momentum is increased as the server swings their arms vigorously, and the opposite side of the body moves in the opposite direction to reduce the total angular momentum (Blazevich, 2010). The vigorous movement of the arm during the serve can be explained through the use of Newtons third law ‘for every action, there is an equal and opposite reaction’ (Blazevich, 2010). The arm movement in the serve creates an equal and opposite reaction rotation in the arms (Blazevich, 2010), where the action of the ball toss arm balances out the action of the racquet arm and by circling the arm in one direction (in this case the racket arm), the body will rotate in the other.

Essentially, when the right arm swings from the front to the back of the body on the sagittal plane-in front past the hip, the more quickly the arm will swing and the more angular momentum it will possess (Blazevich, 2010).

Figure 4: This image is showing the 'foot-up' technique that allows for greater vertical height. Here the athlete has his shoulder and pelvis lateral to the rear tilt during the loading stage, with his arm extended at approximately 100 degrees. This will allow for greater racquet height and shoulder rotation to potentially serve the ball at a high speed. (Kovacs & Ellenbecker, 2011).

Acceleration phase:

In tennis there are many styles of the serve however kick or topspin serves as they are commonly known, are proven to be most accurate to landing in the service box. Kick serves cause the ball to spin at a higher rate which creates aerodynamic forces, where the ball has more curved trajectory, causing it to drop into the service box (Sheets, Abrams, Corazza, Safran & Andriacchi, 2011). More commonly used for second serves, the high percentage of serves that land in the service area have moderate velocity due to the spin and the forces that cause the ball to drop as it slows (Abrams, et al., 2011).

At the acceleration stage, the server will begin by jumping off the ground after the ball has been released and have their knees fully extended for ultimate vertical height. Upon impact of the ball, the racquet arm should be accelerated and extended at approximately 100 degrees, which will allow for optimum velocity. When the racquet comes into contact with the ball Newtons second law is put into place as ‘the acceleration of an object is proportional to the net force acting on it’ (Blazevich, 2010), because the state of motion is going to be changed, the force of the ball is greater and the faster it will move. In saying this, the overall ball speed is determined by the amount of force that is acted on it through the racquet. The product of mass and acceleration, force induces a change in the mobile state of an object (Blazevich, 2010) and therefore the more force applied to the tennis ball during the serve, the greater the acceleration of the serve will be.

 When a force is applied at a distance from the centre of rotation, this is defined as torque (Blazevich, 2010). The rotation of the shoulder and the arm during this serve is caused by the magnitude of the force (Blazevich, 2010) being acted upon, and therefore the rotation of the shoulder determines the speed of the serve. However in saying that as can be seen in figure 5 below, the further the racquet is from making contact with the ball and the greater the height is when the racquet connects with the ball, the greater the moment of force will be due to greater rotation and further distance to gain momentum. Having minimal variability in the hand position when the ball and racquet come into contact means that the ball speed will be increased (Abrams, et al., 2011). In order to increase the speed and velocity of the ball in the serve, the force of the racquet should be increased. This can be done by amplifying the arm speed and increasing the acceleration of the racquet before it impacts the ball. The greater the acceleration of the racquet during this stage, the greater the force will be when the racquet connects with the ball which will then increase the speed of the ball.

Figure 5: Kick Serve. The extended arm of the athlete and impacting the ball at the highest possible point is beneficial as it will produce greater velocity due to the amount of force applied to it from the racquet. The greater rotation of the shoulder as a result of the kick serve, the greater the speed will be. (Tennis about, 2015)

Figure 6: In comparison, this image shows the slice serve. From this image it can be determined that the arm is not extended and thus will not produce as much force and therefore speed. Given that the ball does not hit the racquet at the greatest height possible, the moment of force will not be as high. (Web Tennis, 2015).

Follow through:

The follow through is the last phase of the tennis serve, which generally allows the player to prepare for the next shot. At this phase the body is decelerating after taking the serve, allowing for the body to recover for the oppositions returned shot. During deceleration the server should have prepared themselves for lower body landing and stabilise the trunk (Kovacs & Ellenbecker, 2011). By using the foot-up technique previously discussed, the servers centre of mass will essentially shift forward (Kovacs & Ellenbecker, 2011) due to the force acted upon the body. Centre of mass is the point at which the mass of the body is evenly distributed in all directions (Blazevich, 2010), and for this reason the bodys centre of mass lies within the base of support in order to provide balance. Because there is a force applied at a distance from the centre of mass from the ball connecting with the racquet, it is important not to over-rotate so ground reaction forces are not delivered inappropriately (Blazevich, 2010). After the player has taken the serve it is vital to decelerate and prepare for the next shot to be taken by stabilising the trunk shown in figure 7 below, as this will allow for the centre of mass to be evenly distributed throughout the body in order to provide balance.

Figure 7: The last stage of the service sequence is the lower body landing and deceleration after the shot has been taken. Here it is clear to determine that the athlete has stabilised his trunk and is evenly balanced, therefore his overall centre of mass is efficient. The athlete has not over-rotated as he decelerated which is vital for preparing for the next shot. (Kovacs & Ellenbecker, 2011).

The Answer:

In order to serve an efficient shot that optimises the speed and accuracy of the ball, it is noted that the kick serve is a technique that will allow for advantageous placement in the oppositions service box, and also by adapting the foot-up technique that will provide greater vertical height and potentially a higher speed. These techniques are biomechanically proven to be beneficial to the server, in order to make it more difficult for the opposition to return the ball.

The kick serve is most effective for accuracy and to land in the oppositions service box, due to the high rate in which the ball spins and the aerodynamic nature of the ball. The kick serve allows the ball to drop as it slows down and thus, causes the ball to drop in the opposition’s service area (Abrams, et al., 2011), which may prove to be difficult for the opposition to return the ball. While producing the kick serve is beneficial to the server due to the accuracy it generates, serving a ball with a high speed decreases the likelihood of the opposition being able to return the ball which potentially allows the server to gain more winning points throughout the game. In order to determine the efficiency of the tennis serve, many biomechanical principles have been adapted to establish the most effective ways to serve the ball. Throughout tennis the kinetic chain is extremely involved as the shot is being played, as body movements begin in the lower limbs and as the phases of the serve progress, the limbs of the upper body become predominantly involved. The kinetic chain generates high ball velocity, as do many other biomechanical principles. In the preparation stage of the serve, the non-preferred foot should be lined up diagonally across the court, and the preferred foot parallel with the base line. This will provide good base support of the body, and align the body with the court to determine the direction of the balls intended path. During the ball release phase, the servers angular momentum is increased as they swing the arms, in order to reach high ball velocity (Martin, Kulpa, Delamarche & Bideau, 2012) and the acceleration of the racquet and therefore, the ball (Martin, et al., 2012). This is where the non-preferred side of the body will swing in the opposite direction in order to compensate for the force being acted upon. Through Newton’s third law, the explosive movement creates an equal and opposite reaction in the arms due to the body’s changed state as a result of the angular momentum. The more force that is applied to the ball from the racquet at the perceived distance will also allow for greater acceleration, and the magnitude of the force applied to the ball will determine its speed. Specifically in the acceleration phase, the more amplified the arm speed is and the acceleration of the racquet before it hits the ball will thus increase the force and overall speed of the ball. Predominantly important throughout the last phase of the serve but beneficial to concentrate on in all phases is the centre of mass and ensuring that it is evenly distributed throughout the entire body. By stabilising the trunk after the serve is taken the server is likely to have greater balance which will allow them to prepare themselves for the next shot to be returned to the opposition.

Throughout all of the biomechanical principles stated, it is clear to determine that the serve is accurate and will have a high speed through the use of the kick serve and the foot-up technique. The movement techniques discussed will allow for optimal performance of the tennis serve, increasing the overall outcome to win more points and make it more difficult for the opposition to return the ball.

How else can we use this information?

Identifying biomechanical principles that can assist in serving a ball with greater accuracy and a higher speed will maximise the effectiveness for optimal performance. Through working with biomechanics and understanding skill execution, particular parts of skills can be identified to what needs to be adapted in order for the skill to improve. Because the tennis serve requires many biomechanical principles, the specific skill from this sport can be adapted to many other movements. For example, the serve requires large forward angular momentum of the body, which allows the body to rotate forwards to execute the serve, which can be similarly seen in the ball delivery phase in cricket and also in javelin throwing. Implementing force upon an object can also be adapted to many other sports with racquets or bats such as lacrosse and cricket, as these sports require similar body movements in order to be successful, and speed and acceleration is necessary to be incorporated to most sports today.

By understanding the importance of biomechanics and its use in sport, athletes, coaches and specialists in the field can determine how efficient skill movements are and if improvements are necessary to benefit the athletes performance. Many biomechanical principles can be transferred between sports, so having appropriate knowledge in this field is likely to be beneficial for athletes.

References:

Abrams, G.D., Sheets, A.L., Andriacchi, T.P. & Safran, M.R. (2011). Review of tennis serve motion analysis and the biomechanics of three serve types with implications for injury. Sports Biomechanics, 10 (4), 378-390.

Blazevich, A.J. (2010). Sports Biomechanics, the basics: Optimising human performance. A&C Black.

Flickr. (2012). Tennis Serve Sequence. Retrieved from: http://www.flickr.com/photos/spschofield/6973424295 [Accessed 16 June 2015]

GPP Tennis. (2008). Kinetic Chain. Retrieved from: http://www.gpptennis.com/images/kineticlarge.jpg [Accessed 16 June 2015]

Kovacs, M. & Ellenbecker, T. (2011). An 8-Stage Model for Evaluating the Tennis Serve: Implications for Performance Enhancement and Injury Prevention. Sports Health: A Multidisciplinary Approach, 3 (6), 504-513.

Martin, C., Bideau, B., Bideau, N., Nicolas, G., Delamarche, P. & Kulpa, R. (2014). Energy Flow Analysis During the Tennis Serve: Comparison Between Injured and Noninjured Tennis Players. The American Journal of Sports Medicine, 42 (11), 2751-2760.

Martin, C., Kulpa, R., Delamarche, P. & Bideau, B. (2012). Professional tennis players’ serve: correlation between segmental angular momentums and ball velocity. Sports Biomechanics, 12 (1), 2-14.

Reid, M., Whiteside, D., Gilbin, G. & Elliott, B. (2013). Effect of a common task constraint on the body, racket, and ball kinematics of the elite junior tennis serve. Sports Biomechanics, 12 (1), 15-22.

Sheets, A.L., Abrams, G.D., Corazza, S., Safran, M.R. & Andriacchi, T.P. (2011). Kinematics Differences Between the Flat, Kick, and Slice Serves Measured Using a Markerless Motion Capture Method. Annals of Biomedical Engineering, 39 (12), 3011-3020.

Tennis about. (2015). Point of contact on serve. Retrieved from: http://tennis.about.com/GrigorDimitrov [Accessed on 16 June 2015]

Web Tennis. (2015). Slice Serve. Retrieved from: www.webtennis.com/players/sliceserve [Accessed on 16 June 2015].