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Copy of The Volleyball Jump Serve- A Biomechanical Analysis

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Brandon Harvey

on 3 April 2013

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Transcript of Copy of The Volleyball Jump Serve- A Biomechanical Analysis

The Volleyball Jump-Serve A Biomechanical Analysis By: Cindy, Joanne, Abira and Lior Let's begin with the basics! What exactly is Volleyball What is the jump serve What does the jump serve look like ? ? ? Volleyball is a 2-team game played
The players use their hands to pass the ball, and
the point of the game is to get the ball to land
on the other team's side. across a net! The game takes its roots in the popular
German game of Faustball ("fistball") Fistball is quiet similar to volleyball as the players also utilize their
hands to bat the ball and it also uses a net that divides the teams. In 1895, William Morgan ,a YMCA director in Massachusettes, took the German sport, changed some of the rules as well as
the goals of the game, and gave birth to the game of Volleyball! The game quickly spread all over the world,
and by the end of WW2, an International
Volleyball Federation was established to govern
over 120 national federations! Now that we know some background
about Volleyball, Let's discover what a is! jump-serve A jump serve is a type of serve that involves
the player throwing the ball upward and forward,
sprinting towards it, after a which a jump is made and the ball is spiked over the net! Very similar to a general Volleyball spike,
but in the form of a serve! Watch how it is done for yourself! The jump serve was first demonstrated (officialy) in
the 1982 World Championships by the team , but was first executed effectively during the 1984 olympics by the Brazilian team! Argentinian Used effectively, the jump serve is a against
the opposing team that can score in a point for your team just
from a single serve! crucial offensive move Therefore, it is neccessary to analyze the serve
biomechanically to understand how to truly
perfect it and use it effectively! Every Point is crucial! So let's begin the analysis! Every biomechanical analysis involves
looking at the: 7 Principals So first we need to define the 7 principals and
discuss how they generally (the specifics will come soon!),
apply to the jump serve! Principal 2 - Production of Maximum Force The production of maximum forces requires the use
of all possible joints! Therefore, we get the relationship: More Joints = More Force This is because there will be more
muscles to contract! Now, this principal plays a large role during the jumping
and spiking stages of the jump serve During the Jump: During the Spike: The more joints are used,
(the knees, the hips, the ankles,
etc.) the higher the force that will
be used to lift the player higher! More muscles will be
contracting! The more joints are used,
(specifically the shoulder,elbow wrist and finger joints ) the higher will be the force that the player strikes the ball with!
(helping it travel farther into
the opposing court!) Principal 3- The Kinetic Chain To produce maximum velocity, you need to use the
joints in order from to ! LARGEST SMALLEST Let's focus first on the jumping part of the serve: (Joint order, largest to smallest) Hip Knee Ankle Phalangeal Joints (feet) Now, for the spiking part of the serve. Vertebrae Vertebrae Shoulder Elbow Wrist Phalangeal Joints( hands) Principal 4 Principal 5- Newton's third law Official law: Every action has an equal and opposite reaction Relation to motion: movement will occur in the direction opposite
to the force! Therefore: Force Motion direction direction This principal is found mostly in the sprinting and jumping portions of the serve! When the player sprints, they exert a force against the ground in an angle,
resulting in a motion away from the ground: Force Motion It has to be noted that the direction
of the force is close to parrallel to
the ground, as this will initiate the
sprint! However, when the player needs to jump, the force that they will exert will be more perpendicular towards the ground,so the resulting motion will be in the upwards direction! Force Motion In both cases, for a greater magnitude of motion (more powerful
sprint or a higher jump) a greater force has to be exerted against
the ground! This can be done by quicker, more powerful contractions of legs muscles such as the Gastrocnemius
and soleus. Principal 1- Stability Main concept: A stable position is composed of a: A low centre of gravity
A line of gravity that is within the base
A large base
A lowered mass An unstable position! A stable position! Large base
Low centre of graivty
Line of gravity in base
Lowered mass Small base!
High centre of graivty!
Line of gravity not in base!
Mass is not lowered! During the jump serve, stability is required during the initial
stage of the serve when the ball is first thrown! So when the player throws the ball and begins sprinting,
they will not fall! Stability is also crucial once the serve is complete, so the player will be
in the position to react to an oncoming ball! -Impulse Impulse is the application of force over a certain time period which results
in a change in momentum. Which is basically: Force x Time = Change in Momentum But what is momentum? Momentum is a measurment of how much motion(velocity)
a mass has! So it is basically: Mass X Velocity And relating back to impulse: The more force is exerted over a time period, the larger the impulse, the larger
is the gain of momentum for the object (person), and the larger is the momentum it has, which means larger velocity! F X t = Change in Momen.= More Momen.= V In the jump serve, when the player starts running towards the jump,
they exert a force over time, which results in an impulse that changes
their momentum. This causes their momentum to increase, increasing
their speed! The momentum from the sprint is then transfered to the momentum
of the jump! (So a fast sprint will result in a high jump!) Once a contact is made with the ball, the momentum of the jump is transferred
to the ball. This increases the velocity of the ball, making it go over the net
and far into the opposing court! Momentum is being gained
through sprint! Momentum is transferred
to jump! Momentum is transferred
to the ball! This principal also plays a vital role when the player lands
from their serve! The players must bend their legs such that they will be in contact with the
ground for a longer amount of time! This will result in a smaller force
being transferred over time to the legs (as the impulse remains the same!) Impulse = Force x Time (remains constant) (Increases) (Has to decrease!) Player bends their legs to increase
contact time with the ground
and decrease force on feet! Principal 6 -Production of Angular Motion Angular Motion occurs when a body or a body segment rotates around an axis. The angular motion is caused by a force that acts centripetally known as Torque! (also known as Moment of Force or Turning effect!) Torque causes the "moment arm"
(the distance where the force is applied)
of the object to rotate at a certain
angular velocity!! The torque has to be large enough to
overcome the moment of inertia of the
object it is rotating! This is basically the resistance to a force
by the mass and the distance from axis of
the object! Angular motion is demonstrated in the jump serve when the ball is spiked! During that motion, the arm (moment arm) rotates about the shoulder (the axis), through the use of a force that causes Torque! Bending the elbow during this motion results
in a decrease in the moment of inertia of the arm,
allowing for a faster angular velocity! (for the same amount of force). Angular motion is also present in the jump serve in the form
of projectile rotation! The projectile motion applies to the ball which spins in the air
after being spiked. The spinning affect is created by the "off-centre
force" of the palm of the hand which generated the torque needed
for the spin! The spinning of the ball allows it to be more aerodynamic, and therefore
travel at a faster speed towards the opposing team. Principal 7- Conservation of Angular Momentum Angular momentum is the quantity of motion (just like
linear momentum) of an object that is rotating.
During a rotation, the angular momentum of the object,
remains constant! Therefore, to change one's angular motion during a rotation, as for example, to increase
their angular velocity, they should reduce their moment of inertia! Angular Momentum= Moment of Inertia x Angular Velocity This applies to the fact that when a spike is made during the jump serve,
one must bend their elbow to reduce their moment of inertia and therefore
have a higher angular velocity. Now, that we have covered the 7 principals and how they apply
to the jump serve , let's cover in more depth the phases of the jump serve! Before dividing the Jump serve into its specific phases
it has to be noted that the skill can
be divided into 3 events: The throwing of the ball forwards The sprint and the jump The spike Let's begin first with the throwing of the ball! Even though the event of throwing the ball is quiet simple,
it can still be divided into phases and analyzed through the
principals! Here is a video depicting the throwing motion: Firstly, there is the Preliminary phase of the throw. This is where the player stands with the ball in their hand,
waiting to throw it. Stability (Prin 1) should be maintained during this stage by bending
knees (lowering mass and centre of gravity) as well as maintaining a large base. This is to make sure the player will not fall after the throw when the sprint stage begins. The next phase is the Backward movement phase. The arms are pushed back a bit! This is done to:
A. Increase the distance through which the arm will travel,which will therefore increase the time a force is applied, resulting in a greater impulse
and a greater momentum transfered to the ball (Prin 4).

B. Results in a a large force towards
the back that according to Newton's third law, will mean there will be a large force towards the front due to it being a reaction (Prin 5). The next phase is the force-prducing motion phase. The arms throw the ball upwards and a bit forwards. The momentum that was in the arms was
transferred to the ball (Prin 4). Depending on the amount of force the athelte requires,
he might or might not use as many joints as possible.
(As number of joints used determines force -Prin 2). This is also where the impact phase occurs! The last phase of the ball throw is the follow-
through phase, where the arms follow to ball for
a bit to inhence the accuracy of the throw. If a follow-through is not done,
it is likely that the ball will not be in the needed
position when time comes to spike it! After throwing, the ball, the player must sprint for a bit, building
up enough momentum to jump, and at the end jump high enough
to spike the ball! The Preliminary phase for this event in the skill
is the sprinting! It helps build up the momentum needed for the jump,
by accelerating the player and therefore increasing his/her velocity. This phase also involves the feet pushing against the
ground in accordance with Newton's Third law,
where a reaction force (relatively parallel
to the ground is exerted on the feet). The Backward movement phase in this case is the
bringing of the arms behind the back. It is usually done while sprinting, as the entire skill of
the jump serve happens in mere seconds! This movement once again allows the arms to travel
a greater distance during the jump, which means more
time for the force to act (therefore building up
momentum!) Build up of momentum is crucial for the jumping stage,
as more momentum will mean more Kinetic energy that
will allow the player to jump higher! The Force-producing motion is the jump! During the jump, the arms are swung forward,
gaining even more momentum, and the feet perpendicularly
push against the ground (Newt's 3rd law). Once the jump is initated, the player
still pushes upwards to reach for the ball. For a maximum force, all of the possible joints are used (in both arms and legs), and in the order for largest to smallest (Princ 2-3). Next, the event of the skill now swithces to the actual spiking of the ball! The Preliminary phase for this event in the skill
is the sprinting and the jumping that was done before! They helped build enough momentum for the player to reach the ball
and strike it! The player is now in the air and is preapred to spike the ball to the opposing
court. The backward motion phase in this case will be the arm moving back, behind the head
while the player is in the air! The motion that is being done is angular motion.
This is because the arm is rotating around an axis
(the shoulder), due to the generation of torque. It should be noted that when the phase is being done,
the elbow is flexed in order to reduce the moment
of inertia, and therefore allowing for a higher
angular velocity. The Force Producing Motion Phase is peraphs the most important
phase in the entire skill. It involves the arm moving forward, carefully extneding the elbow from its flexed position,
in order to spike the bal with the palm of the hand. During this motion, most of the momentum is prepared to be transfered to the other ball. Joint use and Joint order is crucial in this step because maximum force
must be applied to the ball, so all of the possible joints (shoulder, elbow, wrist, trunk phalangeal joints) should be used from order of larges to smallest! The next phase in the spike is the impact phase! This is when the palm of the hand makes conact with
the ball, and spikes it over the net! The principal of momentum plays a big role in this case
as a large part of the momentum of the arm is transferred
to the ball! (allowing it to go over the net) Projectile rotation occurs at this stage as the palm of the hand
exerts an offcentre force, therefore resulting in the rotaional
motion of the ball. (The palm of the hand glides across
the surface of the ball creating the off-centre force) The last phase of the Jump-serve skill as a whole is the
follow through phase! This occurs when the arm follows the motion of the ball, increasing the contact with the palm of the hand with the ball (and increasing the generation of the off-centre force, rotating the ball more). It is aso esseintal for the accuracy of the spike! This phase also includes the motion back to the ground after
the jump, and it is here where the concept of force absorption
plays a vital role. If the player lands on the ground while keeping their legs straight
and knees extended rather than flexed, the collision period with the
ground will be very short, resulting in a large force being felt on the feet! This can be very dangerous! However! If the player flexes their knees while falling back down,
the collision time with the ground will be great, which means less
force will be felt on the feet! Now, that we have analyzed the 7 principals of biomechanics
and how they realte to the phases of the jump serve, it is time
for the last piece of analysis. We will now be analyzing an expert who is skilled at the jump serve vs a novice! The expert will be
Subject A The Novice will be
Subject B Firstly, we will begin by comparing the
initial ball-throw of the two subjects. *During the later slides, you can go back to the video
by clicking back It can be clearly seen that not much difference exists between the
ball throw of Subject A vs Subject B. They both generally retain a
somewhat stable position (maximum stability is not needed in this
case as movement will be initated afterwards. However, one small difference that can be seen between the two subjects
is that Subject A has their feet spread apart more while Subject B has their
feet clamped together. Subject A Subject B The wider base of Subject A will result in a stabler position. This is esseintal
for this preliminary phase, because it allows the player to get ready to sprint.
Subject B's smaller base might result in him falling once sprinting is initiated The next phase to be comapred between the two is the
sprinting phase of the jump-serve. Subject A is obviously more successful in the sprint and the subsquental jump than Subject B. This is due to various reasons! Subject A begins their sprint with quick bursts
force due to the use of many joints in order
from largest to smallest!

Subject B on the other hand, does not show
quick bursts of force because they are not using
as many joints for the sprint! This results in Subject A gaining greater impulse
during the sprint, resulting in a greater
gain in momentum. Subject A's greater momentum allowed it to use that momentum to Jump to a high height, while Subject B, who
lacked the needed momentum was not able to perform the
jump. Subject A can also be seen waving their arms backwards,
which is used to gain more momentum before the jump
(so they can jump higher!) The last analysis to be done is that of
the actual spiking of the ball. Subject A is successful in the spike, while Subject B isn't, and once again, there are numerous reasons for this: Firstly, Subject A began their preliminary phase (the jump),at a much higher height than Subject B. This
allowed the ball to be spiked at a much higher height. Moreover, Subject A had performed their backwards motion at a much larger range than Subject B, which allowed for more momentum to be generated during the force-producing motion. During both the backwards motion and the forwards one,
Subject A had a larger angular velocity in regards to the
movement of their arm (due to a smaller moment of inertia),
which allowed for less torque to be used to rotate the arm, and
a larger Angular momentum. During the impact phase, Subject A transferred a much larger
quantity of angular momentum to the ball than Subject B.
This of course allowed the ball to go much further. Subject A
was also much more accurate in regards to their aiming during the impact phase. While in contact with the ball, Subject A was successful
in producing an off-centre force such that a projectile
rotation of the ball will be initiated. Subject A , also used more joints in their lower-body during the
forwards motion which helped produce a larger force. Well, this is the end of the analysis!
Thank you for watching! Therefore, in summary, some of the things that
Subject B should improve upon and the reasoning
behind it are: Balanced stance in beginning- to prevent falling when motion begins More bursts of force should be used during the sprint - to gain more momentum for the jump.
During the spiking of the ball, more joints should be used- increase the force
Also during spike, elbow should be flexed - to decrease moment of inertia
During the contact with the ball a follow through should be done- to increase accuracy/rotation of ball
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