In tennis, the serve is one of the most vital skills for a tennis player to achieve. The primary objective of the serve is to direct the ball into the service area on the opponents side of the court (Emery, 2001). A mix between the speed of the ball and the spot where the ball lands when served, therefore, the accuracy the server can serve to the intended spot can successfully alter the opponent’s ability to return the ball. Elliot (1995) stated that players of all levels certainly seek to develop a high-speed serve as an integral part of their game.

HOW CAN A STABLE STANCE BE ACHIEVED?

Figure 1.1: Tennis player Roger Federer using
a wide legged stance
(source: http://www.improve-your-tennis.com/tennis-serve-stance.html)

During the preparation stage the server will need to achieve a stable stance because they need an even distribution of weight to achieve balance in which will convert to power and accuracy in the continuation of the serve.  

The server will first need to lower their centre of gravity because this can make a person more stable in the fact that centre of mass will be evenly distributed over legs. Lowering the centre of gravity can be done by widening of the legs and a slight bend of the knees. This will also help the server to achieve a greater upwards force because of newtons third law: equal and opposite forces reacting, as the server pushes their legs towards the ground their force is being pushed back helping acceleration of the ball.  

Figure 1.2: Tennis player Thomas Berdych
with his feet together while serving
(source: http://www.improve-your-tennis.com/tennis-serve-stance.html)

When serving the server needs to take a position sideways to the net, the back foot is parallel to the baseline and spread conformably from the front with bent knees to achieve a lowered centre of gravity. Most player will usually start with the racquet out in front of their body. Fig 1.1 and 1.2 shows two different professional tennis players using two different stances. In both examples the tennis player have just tossed the ball and the body has recoiled with different stances. They both use the technique of bent  knees, however, Fig 1.2 shows Thomas Berdych with feet together and fig 1.1 shows Rodger Federer with a wide legged stance. Berdych would not be able to achieve the stability of Federer when performing the serve.

When using a wide legged stance there will be more freedom to be able to move the body weight to your back foot before transferring the weight onto the front foot. However, when Berdych serves the ball with his feet together he can achieve an explosive upwards trajectory towards the ball. He will also be able gain more height summation when contacting the ball, in comparison to Federers wide legged stance.  

HOW DO WE MAXIMISE THE TIME OVER WHICH FORCE IS APPLIED TO THE RACQUET TO SUBSEQUENTLY INCREASE ACCELERATION ON THE BALL?

The time to in which to apply force in a tennis serve is short, therefore, when serving a ball in tennis we need to apply the greatest impulses in very short times by increasing the forces. Blazevich (2012), states the impulse momentum relationship is the greater the impulse, the greater change in momentum. This gives us a hint as to how to best accelerate how body.

The Kinetic chain used in the tennis serve is needed to be able to contact the ball to gain power. Muscle force is used in every element of the chain. In figure 2.1 the first thing you will notice when the is player serving is the fact that they bend their knees a significant amount before the serve.  When the ball is tossed the body will recoil with the upper body rotated. Next you will notice the upward drive of the legs to accelerate to the ball by straightening the legs in an upward motion. This will assist in increasing the acceleration of the arm to increase the racquet head speed to be converted in to the ball. According to Newton’s third law, as the athlete pushes against the ground, the earth pushes back up against the athlete with the same force, this is also known as a ground reaction force (Carr,1997, p.20). The last of the sequence is the follow through caused by momentum of the swing after hitting the ball. The momentum will propel the server forward into the court ready to play the next point.



Extra acceleration is accomplished by contacting the ball just in front of the body so weight is easily transferred forward into the ball. Otherwise if the ball is behind their body much of their force will be lost.



figure 2.1: the kenic chain of movements during a tennis serve
(source: http://optimumtennis.net/power-tennis-serve.htm)

Newtons second law: 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) is apparent when to increase the speed of the ball when contacting the ball during the serving motion as you need to accelerate the ball from the force of the racquet.

The point of contact is vital to increase the speed of the serve. The server will need to contact the ball at the top of the reach to ensure the most amount of their power and force in transferred into the ball. This is because longer arm length the faster the velocity of the racquet head. The speed of the racket head at impact is therefore a critical feature of a successful serve that can be varied considerably by the player, particularly through the individual movements.

The ball toss may need to be altered to gain more time between the recoil stage and contacting the ball. If the ball is tossed higher it will result in more preparation time. The server will consequently be gain more time in which to apply muscle force.

WHAT DETERMINING FACTORS WILL CHANGE THE FLIGHT OF THE BALL, THEREFORE, ALTER THE ACCURACY OF THE SERVE?

When serving the ball the aim is to be able hit over the net and land in the opposite side of the court, otherwise it will be deemed as a fault. The flight path of the ball will be determined by many different factors. Therefore, the server will accurately need to place the ball in the intended spot.

The body sequence that makes up the kinetic chain for the tennis serve include an optimal racquet position, trajectory, and velocity in which are apparent at impact of the ball. Interruption to this sequence will reduce the effectiveness of the serve (Elliot, 1988). Tennis players use a throw-like motion to increase ball speed while still being able to achieve high levels of accuracy (Blazevich, 2012). This is because the skill of serving is closed down because the server is in control of every chain of movement.

When the server comes in contact with the ball the angle of the racquet will alter the angular displacement, therefore, flight path of the ball. In figure 3.1hows the red arc has a racquet face where it is slightly in a laid back position when in contact, it will cause the ball to travel in a higher arc. Alternatively, blue arc the racquet is facing too far to the ground it will cause the ball to drop short possibly hitting the net. Therefore, the player will need to hit the at an angle in-between the two so the ball has plenty of room to clear the net.



Figure 3.1: different flight paths of the ball when hit with the raquet at different angles 



Projectile speed will also alter the flight path of the ball, the faster the ball is hit the further it will travel. However, the server needs to have a balance of speed and accuracy, because if the ball travels too far it will result in a faulty serve.

As well as the position of contact, the flight path of the ball can be altered position of the shoulders. Open shoulders parallel to the service line and closed when they are perpendicular to the service line. When the shoulders are open there is usually a tendency to hit the ball wide, whereas, when they are closed  

HOW CAN THE TYPE OF RACQUET USED ALTER THE LEVEL OF POWER AND ACCURACY THE SERVER CAN EXHORT ON THE BALL?

When a tennis player is in the beginning stage their tennis player usually will use a racquet  that has a large face, small handle and is light weight. The exaggeration of the racquet may also vary with age as well as experience.

Having a larger racquet face will increase the sweet spot on the racquet. According to Cross (2006) the sweet spot on the tennis racquet can be defined as the impact point that maximizes the implosive forces transmitted to the hand. As shown in fig 4.1 when the size of the tennis racquet is enlarged so does the sweet spot. This evidently will make it easier for a beginning player to be able to make contact with the ball because the overall contact area is enlarged and the racquet is light. So then why don’t all experienced players use an oversized racquet? This is because experienced player don’t have to worry about things like coordination so they can sacrifice using a larger racquet to be able to focus on other factors such as force generation and control.



Figure 4.1: the larger the size of the raquet heads the larger the sweet spot
(Source: http://www.milletsports.co.uk/guide/tennis/)



When a tennis player becomes autonomous, tennis players will usually select to use a heavier racquet, with a smaller face, longer handle and alter the string tension to their liking.

When serving the ball in tennis there is a limited amount of time in which to apply force. Therefore, using a heavy racquet with assist with the amount of force generated on to the ball. If a tennis player wants to be able to move the racquet quicker, therefore, generate a larger amount of power, the heavier the racquet will need to be as long as inertia is overcome. The more mass the racquet has the momentum the racquet can exhort.

The tension of the racquet will determine how far the ball is going to fly, the tighter the strings the greater the level of control and power increases with loser strings. This is because of the coeffiencent restitution in which is the numerical index of elasticity (energy retained) after a collision of two bodies (Blazevich, 2012). When the racquet string tension is modified it can changes the level of power and accuracy. When the string tension is loosened there is more give on impact and this propels the ball off the racket face at greater speed.

THE ANSWER

Power and accuracy can be optimised in a tennis serve from a variety of aspects. The kinetic chain is the group of movement that make up the serve, if any of these are interrupted it will reduce the effectiveness of the serve.

To be able to increase power production the server will first need to overcome inertia within the serve. When that is accomplished the server will need to focus on increasing the speed of the racquet head, the height of contact, muscle force and stance for the summation of power.

When the server wants to accurately position the ball when served they need to determine the flight path the ball will obtain. There are many contributing factors that will alter the flight path such as the angular displacement of the racquet, the speed in which the ball is hit and shoulder position.

However, when modifying the racquet both accuracy and power are altered. With a larger racquet comes a larger sweet spot area consequently making it easier to make contact with the ball. Experienced players will often request a modified string tension of the racquet. The loser the string the more power the user can exhort of the ball.

However, there are many other factors not mention in this blog that can alter both accuracy and power. Some example can include spin imparted on the ball such as top spin and back spin, the Magnus effect, curve of the balls flight path, different serving positions and the reasoning to serve at different position e.g. serving further away from the centre in a doubles match, wind and strategies for determining what serve you would like to use.

 

REFERENCES

Carr. G. (1997). Mechanics of Sport: A Practitioner’s Guide. Windsor: Human Kinetics.

 

Cross. R (2006). The sweet spots of a tennis racquet [online]. Available: http://www.physics.usyd.edu.au/~cross/sweetspots.pdf. Physics Department. Sydney, NSW.

 

Blazevich. A, J (2012). Sport Biomechanics the Basics: optimising human performance. 2edn. A&C Black.

 

Elliot, B. C (1988). Biomechanics of the serve in tennis. Volume 6, Issue 5, pp 285-294. Sports Medicine  

 

Emery, G. (2001). Biomechanical Analysis of the Tennis Serve