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