INTRODUCTION 

The tennis serve is one of the most important moments the player has in a game of tennis.  The serve is the only part of the game where the player has full control; however, it can be difficult to successfully master as it involves complex coordination of lower and upper body parts (Hussain, Hussain, Ahmad, 2015).  The tennis serve is broken down into four phases; preparation, wind up, connection, and follow through.  Each of these phases has a variety of biomechanics principles that allow the server to have a successful outcome with the serve. 

THE QUESTION

What biomechanics principles are required to perform the optimal tennis serve?

PREPARATION PHASE

The preparation phase for the tennis serve does not include a lot of biomechanical principles.  At the start the server has to mentally prepare before they serve the ball.  During this phase the server thinks about what type of serve they are going to serve to their opponent, and establishes the location of where their opponent is standing (Kovacs & Ellenbecker, 2011).  A biomechanical principle that is used during this phase of serve is centre of gravity.  Centre of gravity can play an important role whilst preparing for a serve.  Having a good centre of gravity when serving in tennis allows all the particles of the body to be evenly distributed through out the whole body (Blazevich, 2012). With having this it creates the perfect balance for the server.  For the preparation phase the goal is for the players body to be align with the ground for force and power generation, which will help in the next phases of the serve (Kovacs & Ellenbecker, 2011).  

WIND UP PHASE

As the server tosses the tennis ball up, the next movement phase for the serve starts.  The purpose of the wind up phase is to generate as much force as possible for the third phase, which is the connection of the racquet and tennis ball.

Kinetic Chain

For the server to achieve a successful tennis serve there must be movement from the whole body (Wong et al, 2014).  During the wind up phase in the tennis serve the kinetic chain is a key source for successfully completing the serve.  The kinetic chain stated by Blazevich is where there is a link segments of a body that move together (Blazevich, 2012). 

 Kinetic chain event in tennis serve image from http://www.gpptennis.com/VideoTools.html

There are two important categories in the kinetic chain; push like movement pattern, where all the joints are extended in a single movement, and throw like movement pattern, where the joints extend in a sequence one after the other (Blazevich, 2012).  Both categories for the kinetic chain are relevant during the wind up phase of the tennis serve, which help with the power, and accuracy of the serve.

During the first category in the kinetic chain event, the push like movement pattern during the serve is where the lower half of the server’s body pushes off the ground to create an upward force.  This part of the serve relies on the large leg muscles to provide the majority of power to allow the server to explode in an upward direction towards the tennis ball.

The pull through movement pattern is where the trunk muscles pull the trunk and arm from cocking into ball impact (Kibler, n.d).  It also creates a long axis rotation in the arm.  The pull through movement pattern does not rely heavily on the knee flexion and the leg muscles (Kibler, n.d).  The muscles during the kinetic energy chain that produce the most are the trunk and legs, which use 51%.  The shoulder follows that at 13%, and then the elbow at 21%, and lastly the wrists produce 15% of kinetic energy (Ellenbecker, De Carlo, & DeRosa, 2009).

Ground Reaction Force

The push like pattern can also be described through Newton’s Third Law. Newton’s Third Law states that every action has an equal and opposite reaction (Blazevich, 2012).  During the wind up phase when the tennis player tosses the ball the server prepares their feet by pressing down on the court and bending their knees to lift to make contact with the ball (Merritt, 2012).  When the players are putting force into the ground they are creating an equal and opposite reaction in the other direction, which allows them to move upwards (Merritt, 2011).  The image below is a demonstration of the servers feet when pushing into the ground creating an equal and opposite reaction to allow moving in an upward direction (Kovacs & Ellenbecker, 2011).

 Image: (Kovacs & Ellenbecker, 2011)

Centre of gravity

Having a good centre of gravity is very important in the wind up phase of the tennis serve.  Once the preparation phase is over and the server is starting on the wind up phase the servers centre of gravity is shifted backwards.  The server shifts their centre of gravity backwards to allow their racquet arm to fully extend behind their back.  With the server extending their racquet arm backwards this will create a greater distance for the racquet to contact the ball, which results in having an increase on the speed of the serve.  The image below demonstrates Rafael Nadal’s centre of gravity being shifted backwards during the wind up phase to prepare for his racquet to make contact with the tennis ball. 

Image from: http://www.zimbio.com/pictures/iCR_-ku7Kna/2010+French+Open+Day+Seven/OAV1wC529kq/Rafael+Nadal

Torque

Torque described by Blazevich is where the magnitude of the force causing the rotation of an object (Blazevich, 2012). Torque can be related to the tennis serve as the player’s arm, racquet, torso, and legs all rotate during some point of the serve.  The video below is of tennis player Novak Djokovic.  In the video you can see Djockovic’s body rotate during the serve.  Torque in a serve is important as when the body rotates it gives the server momentum to go forward in the next phase, which will increase the speed of the ball.

Video from https://www.youtube.com/watch?v=uyTtZE6LSek

CONNECTION PHASE

The next phase is the connection phase.  This phase is the most important phase of the serve as it determines how the tennis shot will be played.  The connection phase, just like the other phases have biomechanical principles that help improve the outcomes when the racquet connects with the tennis ball.

Centre of gravity

Just like the first two phases, centre of gravity is still extremely important in the connection phase.  As mentioned in the wind up phase the servers centre of gravity is shifted backwards.  During the connection phase the server starts to shift their weight in a forward direction.  When the server shifts their centre of gravity forward this creates a greater force and momentum, which then increases the speed of the tennis ball when the racquet connects.  The image below demonstrates the shift in centre of gravity from the wind up phase into the connection phase.  The first image is Rafael Nadal with his centre of gravity backwards and then the second image is where his centre of gravity has been shifted forward during the connection of the racquet and ball

Image from: http://www.fredmiranda.com/forum/topic/1268147

Newton’s Second Law

Newton’s second law is evident in the connection phase.  As Blazevich has stated Newton’s second law is when ‘the acceleration of an object is proportional to the net force acting on it and inversely proportional to the mass of the object’ (Blazevich, 2012, p 43).  This is related to tennis, as the tennis ball remains the same mass throughout the serve.  Which then results in the tennis ball travelling faster when hit with a greater force, which can lead to an ace.

Continuing on from the wind up phase Newton’s third law is still relevant in the connection phase as the player is still pushing upwards from the ground reaction force.   

Magnus Effect

The Magnus effect is explained where a spinning ball moves through the air, and whilst the ball is spinning a boundary layer of air clings to the surface. ‘On one side of the ball the boundary layer of air collides with air passing by. The collision causes the air to decelerate, creating a high-pressure area. On the opposing side, the boundary layer is moving in the same direction as the air passing by, so there is no collision and the air collectively moves faster. This sets up a low-pressure area. The pressure differential, high on one side and low on the other, creates a lift force (the Magnus force) that causes the ball to move in the direction of the pressure differential (i.e., from high to low)’ (Human Kinetics, n.d).  The image below demonstrates the Magnus effect on a tennis ball during a serve

 Image from: https://plus.maths.org/content/spinning-perfect-serve

A tennis player serving a fast serve can be an extremely successful move in tennis.  However, all opponents can adapt to serves if the serve is repeated a few times (Thomas 2012).  The successful serves come when the player keeps the opponent guessing on how the ball will be delivered (Thomas 2012).  By using the Magnus effect and putting a spin on the ball it achieves the task of having the opponent not sure on how the ball is going to bounce (Thomas 2012).  When serving, the server can hit the tennis ball to create a certain spin.  A sidespin can be applied by the server, which then will cause the Magnus effect to make the tennis ball to curve to one side (Thomas 2012).  The image below is an example of when a tennis ball is hit with a sidespin, which causes the tennis ball to curve to one side (Thomas 2012).

Image from: https://plus.maths.org/content/spinning-perfect-serve

FOLLOW THROUGH

The last movement phase for the tennis serve is the follow through.  Many elite tennis players will finish the serve inside the tennis court.  With finishing inside the court that suggests that the tennis player’s momentum is moving forward, which is important in a serve and especially from the last phase (Waite, n.d.).  Centre of gravity is also important during this phase as if the center of gravity goes too far forward the player can loose their balance and struggle to prepare for the next shot.  The image below demonstrates Rodger Federer during the serve.  You can see from the last frame Federer’s follow through and his balance, are inside the line, which makes him prepared for the return of the next shot.   

 Image from http://www.stevegtennis.com/roger-federer-serve-analysis-and-slow-motion/

THE ANSWER

There are many optimal biomechanical principles to create a successful tennis serve.  Biomechanical principles such as, Newton’s first and second law are very important when wanting the optimal tennis serve.  Centre of gravity is one main biomechanics principles in a tennis serve as it is demonstrated in each of the four phases.  With out having centre of gravity, the server will loose their balance, which will result in a poor executed serve.

HOW ELSE CAN WE USE THIS INFORMATION?

Coaches can use this information of the biomechanics of a tennis serve to improve young and beginner tennis players with their serve.  The biomechanics principles that have be shown for the tennis serve can be easily transferred to similar sports, such as badminton, table tennis, and baseball where using a racquet or bat is involved.   The Magnus effect explained for the tennis serve can relate to other sports, such as soccer, golf, and baseball as each sport can use the Magnus effect of curving the flight path of the ball.

REFERENCES 

Blazevich, A, (2012), “Sports biomechanics, the basics: Optimising human performance,”London: A&C Black

Ellenbecker, T. S., De Carlo, M., & DeRosa, C. (2009). Effective functional progressions in sport rehabilitation. Human Kinetics.

Essential Tennis. (2013). Novak Djokovic Serve In Slow Mo YouTube, retrieved from https://www.youtube.com/watch?v=uyTtZE6LSek

Human-kinetics,. Magnus effect. Retrieved 19 June 2015, from http://www.humankinetics.com/excerpts/excerpts/magnus-effect-

Waite, R. Moving To The Ball. Tennisserver.com. Retrieved 19 June 2015, from http://www.tennisserver.com/turbo/turbo_10_12.shtml

Hussain, I., Hussain, S. A., & Ahmad, F. (2015). Influence of Body Kinematics on Tennis Serve.

Kibler, B. Aspetar Sports Medicine Journal - The kinetic chain in tennis: Do you push or pull?. Aspetar.com. Retrieved 19 June 2015, from http://www.aspetar.com/journal/viewarticle.aspx?id=6#.VYP4IRbrpFJ

Kinetic chain Event image retrieved from http://www.gpptennis.com/VideoTools.html

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.

Magnus Effect Image retrieved from: https://plus.maths.org/content/spinning-perfect-serve

Merritt, C. (2011). How Does Newton's Laws of Motion Interact With Tennis? | LIVESTRONG.COM. LIVESTRONG.COM. Retrieved 19 June 2015, from http://www.livestrong.com/article/401315-how-does-newtons-laws-of-motion-interact-with-tennis/

Rafael Nadal Tennis Serve Image,
Retrieved from http://www.zimbio.com/pictures/iCR_-ku7Kna/2010+French+Open+Day+Seven/OAV1wC529kq/Rafael+Nadal

Rafael Nadal Tennis Serve Image, Retrieved from http://www.fredmiranda.com/forum/topic/1268147

Rodger Federer Image, Retrieved from http://www.stevegtennis.com/roger-federer-serve-analysis-and-slow-motion/

Thomas, R. (2012). Spinning the perfect serve. Plus.maths.org. Retrieved 19 June 2015, from https://plus.maths.org/content/spinning-perfect-serve

Waite, R. Moving To The Ball. Tennisserver.com. Retrieved 19 June 2015, from http://www.tennisserver.com/turbo/turbo_10_12.shtml

Wong, F. K., Keung, J. H., Lau, N. M., Ng, D. K., Chung, J. W., & Chow, D. H. (2014). Effects of body mass index and full body kinematics on tennis serve speed. Journal of human kinetics, 40(1), 21-28.