Major Question
The tennis serve
is a very complex system within the sport. By being competent in the tennis
serve at a professional level can inhibit your performance depending on the
return game of their opponent. The best servers in the game; Roger Federer,
Tomas Berdych, Stan Wawrinka, and Novak Djokovic, to name a few, rely on their
serve to get them out of trouble in certain situations. Throughout this blog, I
will cover some biomechanical principles with using elite servers to indicate
the optimal tennis serve to create power. I will look at certain aspects
jumping into the serve, the tossing arm during serve, the serving arm during
the wind up phase, trunk position during the wind-up phase, and the racquet
head contact with the ball.
The Answer
1.
Jumping into Serve
Above is a
professional tennis player called Tomas Berdych. Notice his head stays
relatively still and isn’t looking away from the ball. By not taking his eyes
off of the ball and keeping his head still, helps him to improve his accuracy
of the tennis serve. The red dots
highlight where his centre of mass rises and falls while he’s jumping into the
air. By manipulating his centre of mass in small increments helps him to create
a stable base of support. With creating a lower centre of mass helps with
stability that enables his head and eyes to focus on the ball (Beachle &
Earle, 2008).
Berdych is able
to manipulate his body parts (legs, arms, torso) due to conservation of
momentum. As Berdych jumps he tucks his legs underneath his body, and then
extends them downwards rapidly, to help push his upper body upwards, this is to
help enable him to conserve momentum. This relates to Newton’s 1st
Law states “that every object will remain at rest or in uniform motion in a
straight line unless compelled to change its state by the action of another
force (Grc.nasa.gov, 2015).” While Berdych is jumping upwards, gravity is the
other force which is acting downwards, by extending his legs rapidly, he
creates a force that requires an equal and opposite reaction to his legs,
pushing his upper body upwards, giving him more time to “hang” in the air
before gravity acts down on Berdych again
2.
Tossing arm during serve
Balzevich (2007) states, “angular momentum is a function of mass and
velocity, in this case the velocity is angular and the mass is at a distance;
that is, it has a moment of inertia (Grc.nasa.gov, 2015).” This results in
Newton’s 3rd law, “for every angular action there is an equal and
opposite angular reaction.” Looking at Stan Wawrinka’s ball toss arm below, we
can see once he has release the ball, his arm is straight. After the arm has
straightened, and Stan starts to produce his throw-like movement pattern, the
ball toss arm starts to drop and produce angular momentum. The quicker the arm
is pulled down with a bent elbow and closer towards the midline of the body;
the moment of inertia has a decreased effect on the conservation of angular
momentum and increased the rotational velocity of the body. Through swinging
this arm vigorously, another part of the body e.g. the hitting arm will tend to
rotate in the opposite direction to reduce the total angular momentum. Stan’s
ball toss arm is always kept close to his body to reduce the effect the moment
of inertia that the arm has on the rest of his body. While serving it is best
to visulise pulling your elbow towards your hip, instead of pulling your hand
down towards you leg.
If Wawrinka was to pull his arm down vigorously while it’s still
straight, then his body will over rotate and possibly lift (jump) into the air
too high, and if he pulled his arm down softly, while still being straight, he
wouldn’t rotate enough.
3.
Serving arm during wind-up
phase
When the tennis
ball is at its highest point, it has zero momentum. This relates to Newton’s 1st
law “an object will remain at rest or continue to move with constant velocity
as long as the net force equals zero.” Once the tennis ball has zero momentum
Newton’s 2nd law comes into practice, “the acceleration of an object
is proportional to the net force acting on it and inversely proportional to the
mass of the object: F = ma.” Essentially when the player tosses the ball into
the air, they have applied a force upwards, with gravity applying a force
downwards, this then creates a point in time when Force equals zero due to
acceleration becoming zero for a very short time. This short amount of time is
the optimal time to apply a force to the ball.
Balzevich (2007)
states “the more particles that are further from the pivot point, the larger the
moment of inertia.” In the case of the serving arm, the further away the racquet
head is from the pivot point, which is the shoulder, the greater the moment of
inertia will be exerted on the ball. Novak Djokovic, who is one of the best
servers in men’s professional tennis, strikes the ball at the highest point.
This is shown in Figure 1 where his hand is closest to the end of the racquet.
However, to produce this large amount of force upon the ball he also uses a
throw-like movement pattern. Initially, Djokovic creates angular momentum at
the base (shoulder), and he then uses the proximal muscle groups to produce
large amounts of force within the shoulder to transfer that energy to the
distal segments (hand and fingers). In
figure 2, shows the example of how the joints in the kinetic chain extend
sequentially, one after another. The shoulder extends before the elbow and
wrist; the shoulder begins to extend before the elbow is still flexing. Towards
the end of the throw the extension of the hands and fingers increases
significantly.
In a tennis
sense, Roger Federer shows how a throw-like movement pattern is used in the
tennis serve. His shoulder extends towards the ball with the elbow and wrist still
flexing. He generates a large amount of force with the shoulder and transfers
that force into the elbow, through to the wrist, to the hand and fingers, and
finally to the racquet head where the force generated at the shoulder has
increased significantly.
The transfer of
momentum leads to Netwon’s 1st law. The main principle of the
transfer of momentum states that momentum cannot be lost – it is just
transferred from one object to another (Beachle & Earle, 2008). This
transfer of momentum is prominent in all aspects of tennis, especially the serve,
to help develop power, by transferring momentum from the shoulder to the arm,
wrist, hand, fingers and tennis racquet into the tennis ball. Essentially the
greater the momentum that is produced through the shoulder, the greater amount
of momentum will be transferred into the ball.
4.
Trunk position during wind-up
phase
To help create the throw-like movement pattern, which is a summation
of force, we need to create more force through the lower limbs to generate more
power (Beache & Earle, 2008). Using the example above with Roger Federer,
notice how initially he uses his back leg to stabalise, but also start to
generate force. This is then transferred from the leg(s) into the trunk,
through the arm/shoulder. This is shown in the figure below. Federer’s technique shows
that he transfers his weight not only from his back leg, but from his front leg
as well, then the rotation from his lower torso into his core, and finally his
shoulder. Federer's torso is roughly perpendicular to the baseline on the tennis court, this is to ensure that he does not over rotate and cause harm to his back.
5.
Racquet Head contact with Ball
With the summation of forces acting on the tennis ball
while it is in the air equaling zero, when the racquet head contacts the tennis
ball, the contact time (impulse) needs to be as small as possible. Impulse is
the amount of force needed to change the momentum of an object varies depending
on the amount of time that force is applied. The formula for impulse is shown
below:
Impulse = Force x Time
It may make logical sense to apply a smaller force over a longer
amount of time while serving, however to ensure that we have enough time to
contact the tennis ball with the racquet would not suffice. Through
transferring momentum in the wind-up phase, the impulse needs to rely heavily
on the force and not the time (Beache & Earle, 2008)
How Else Can We Use this Information?
Through
analysing a few of the major components of the tennis serve, this blog has
identified major components of the tennis serve. By applying and utilising
these biomechanical principles highlighted above should help increase the
performance and power of the tennis serve. These principles can also be incorporated into the other components of tennis (e.g. groundstrokes and volleying).
References
Neuroanthropology,. (2009). Throwing like a girl('s brain).
Retrieved 16 June 2015, from http://neuroanthropology.net/2009/02/01/throwing-like-a-girls-brain/
Baechle, T., & Earle, R. (2008). Essentials of strength
training and conditioning. Champaign, IL: Human Kinetics.
Grc.nasa.gov,. (2015). Newton's Laws of Motion. Retrieved
16 June 2015, from https://www.grc.nasa.gov/www/K-12/airplane/newton.html
YouTube,. (2015). Stanislas Wawrinka Serve In Super Slow
Motion - 2013 Cincinnati Open. Retrieved 16 June 2015, from https://www.youtube.com/watch?v=_xmJO_ZUtWU
YouTube,. (2015). Roger Federer Serve In Super Slow Motion -
2013 Cincinnati Open. Retrieved 16 June 2015, from https://www.youtube.com/watch?v=FBkFgS3e4QY
YouTube,. (2015). Tomas Berdych Serve In Super Slow Motion -
2013 Cincinnati Open. Retrieved 16 June 2015, from https://www.youtube.com/watch?v=WgnUVg5snss
YouTube,. (2015). Novak Djokovic Ultimate Slow Motion
Compilation - Forehand - Backhand - Serve - 2013 Cincinnati Open. Retrieved
16 June 2015, from https://www.youtube.com/watch?v=C5n84AqUyGA
