Introduction
Netball is the most popular sport in Australia played
by women with an estimated amount of one million players playing nationwide (Netball Australia, 2015).
Netball is a very fast paced, skillful game that not only requires players to
have speed, agility and endurance but also relies greatly on teamwork. Netball
is a team sport that requires seven players from each team on the court at a
time, with each only allowed in specified areas during play. The positions can
be separated into two groups: the attackers and the defenders. The goalkeeper,
goal defence and wing defence make up the defenders. While the wing attack,
goal attack and goal shooter make up the attackers. The centre is included in
both groups. Netball goal shooting is a major component within a netball game
and as stated by Steele (1990) ‘shooters shoot goals and goals win games’. The
ability of a goal shooter to successfully score goals is a major aspect within
a game, therefore goal shooters must be able to understand the biomechanical
principles of goal shooting and be able to get into a preferred shooting
position as quickly as possible.
Image 1: Netball court and player positions
What is sports biomechanics?
Blazevich defines biomechanics as the “field of
science devoted to understanding mechanical principles in relation to
biological organisms” (2010). In order to achieve optimal technique in any
skill, we must understand what factors influence the technique and what is
considered optimal. Analysing a skill from a biomechanical perspective allows
for optimising performance techniques.
This blog will
demonstrate the specific biomechanical factors that are required for optimal
execution of the netball goal shot.
The Answer
What are the biomechanics of the netball shot?
The biomechanics of a successful goal shoot are
listed below and each of these can have a major impact on the success of
scoring a goal in a netball game.
There are three major phases of movement in regards to
the netball shot, which are;
Preparation Phase
Release Phase
Follow through Phase
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Each of these phases have biomechanical principles as
well as skill cues which relate directly to the phase and need to be understood
in order to be executed successfully.
Video 1. Phases of a goal shot in motion.
Video 1 shows the stages of the netball goal shot and how they link into one another. It will demonstrates the optimal performance that is going to be detailed below.
Preparation Phase – Balance and Stability
What is included in the preparation phase of the netball goal shot?
The preparation phase consists of the movements that help prepare an athlete for the performance of a skill (Pyke, 2010). To determine whether or not to shoot is a decision that every goal shooter or goal attack has to make when in the goal ring in a matter of seconds. The three key factors that influence this decision are: balance, distance from the goal ring and the position and availability of the other shooter (Woodlands, 2006).
Balance
A netball player must be able to find their centre of
mass in order to achieve balance when preparing for goal, which is done by
identifying the point at which the body is evenly distributed in all directions
(Blazevich, 2010). Balance (equilibrium) is an essential component in preparing
to successfully execute this skill. Balance can be effected by Newton’s First Law,
“An object will remain at rest or continue to more with constant velocity as
long as the net force equals zero” (Blazevich, 2010, p.44). This means that
when the forces acting upon the body
equal zero, a state of equilibrium is achieved (Pollock,
Durward, Rowe, & Paul, 2000). Being balanced allows for the goal shooter to
prepare to take a shot. The quicker balance is achieved the more time there is for decision making, skill execution and processing other factors influencing the goal.
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| Figure 1: Centre of Gravity changes in different positions. |
Distance
The distance
from the goal post can have a great impact on the overall accuracy of the netball
shot as the further away from the ring the shooter is, the less likely it is that a goal will be scored. Steele (1993) states that the
distance from the goal post when shooting highly influences the accuracy of the
overall shot while Woodlands (2006) states that ‘experienced shooters know their range and how far out they can shoot confidently’. When further from the goal ring greater flexion of the elbows and knees is required in order
to generate more force.
Position
After receiving a pass in the goal circle the first
foot to touch the ground (the grounded foot) is not allowed to lift off of the
ground. A pivot is required to face the goal ring, resulting with feet being in
line with the goal ring. It is important to ground the second leg at shoulder
width apart to form a balanced base of support, which will provide stability (Blazevich,
2010). In an upright steady position the body’s centre of gravity will be in
line with the base of support (Figure 1), which results in being balanced and not swaying involuntarily. If the centre of gravity is displaced
outside of the base of support the body will become unsteady and begin to fall
(Pollock, Durward, Rowe, & Paul, 2000).
Skill Cues
"Land in a position that will assist with gaining balance quickly."
“Stand with feet shoulder width apart with relaxed
knees.”
“Keep feet facing towards the goal post.”
"Limit trunk movement to assist balance and stability."
“Raise ball above head using preferred hand while
supporting with the other hand.”
How can the preparation phase help the accuracy of the netball goal shot?
The preparation phase helps the shooter maintain balance and stability when performing the netball goal shot and allowing for successful completion of the following phases, which can then lead to a goal being scored.
Release Phase – Power production
The
release phase of a netball shot requires force, which is gained by using a push
like movement by extending the knees and elbows in an upright position towards
the goal ring. The release phase also requires the shooter to flick both wrists
as the ball leaves the fingers in an upwards direction through a backwards spin
which helps the trajectory of the ball.
Newton’s Laws
Newton's Laws can be incorporated into understanding the netball shot by allowing netball players to get a better understanding of the science behind the successful shooting technique of scoring a goal.
Within the phases goal shooters must also learn to maneuver within the goal circle to become closer to the goal post to increase the chance of scoring the goal. Furthermore, constraints such as defenders, weather and personal ability (Davids, Button, Bennett, 2008) can all have an impact on a goal shooter's chance of performing an accurate goal shot. Practice with the use of constraints can benefit and improve the goal shooter's ability to over come issues they may face during a game situation.
Force
Blazevich (2010) defines force as being 'the product of mass and acceleration; induces a change in the mobile state of an object". Force helps to set up and determines whether or not a
ball will make the distance when shooting for goal. Within netball the force of
the shot can be described as a push-like movement where all joints are
simultaneously extended. This movement generates force that is transferred through the body to the ball.
Projectile motion
The projectile motion refers to the motion of an object that is projected into the air at an angle. The projectile motion within the sequence of the netball shot plays a vital role in completing the shot successfully (Figure 2). When a netball goal shooter is attempting a shot at goal, they need to release the ball at an angle that is big enough in order to obtain sufficient vertical height to reach the goal ring.
The projectile motion refers to the motion of an object that is projected into the air at an angle. The projectile motion within the sequence of the netball shot plays a vital role in completing the shot successfully (Figure 2). When a netball goal shooter is attempting a shot at goal, they need to release the ball at an angle that is big enough in order to obtain sufficient vertical height to reach the goal ring.
Figure 2. Angle of release at 60 degrees to ensure correct vertical height and range are reached.
Newton's Laws can be incorporated into understanding the netball shot by allowing netball players to get a better understanding of the science behind the successful shooting technique of scoring a goal.
Newtons First Law: Inertia
‘An
object will remain at rest or continue to move with constant velocity as long
as the net force equals zero’ (Blazevich, 2010, p.44).
This means that to change the state of motion of an
object, a force must be applied. Inertia means that an object will continue in
its current state of motion. The mass of an object determines how easily the
state of inertia can be altered. Inertia is relational to the mass of an object: larger objects have a greater mass and therefore greater inertia. Buses for example have a large mass and will
require a greater force to change the state of motion, to increase or decrease
velocity or to change direction.
The distance from the ring when preparing to shoot
will determine the force that is needed to be applied to the ball (to change the state of inertia) in order to increase its velocity and project the ball towards the
ring.
Newtons Second Law: Acceleration
‘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’ (Blazevich, 2010, p.45).
The acceleration of an object is determined by its
weight and the force applied.
Force =
Mass x Acceleration
If an object is lighter it will accelerate faster
under a given force. This law is demonstrated when the ball is released from
the hands, it accelerates, and moves towards the target. The amount of force
applied on the small object needs to be appropriate as to not over shoot the
target.
Newtons Third Law: Action/Reaction
‘For
every action, there is an equal and opposite reaction’ (Blazevich, 2010, p.
45).
When the ball is released there is a force applied to
the ball in order to project it through the air and change its state of motion.
When considering energy it is important to remember "energy can neither be created nor be destroyed" (Dincer, 2002). Whether the goal is successful
or not depends on how this force is transferred. If the goal is successful the
ball will hit the ground and the opposite reaction is the force that causes the
ball to bounce upwards. If however the goal is unsuccessful and optimal
technique has not been implemented then the equal and opposite reaction occurs
when the ball rebounds off the ring and travels in another direction. In either
instance, the force from the shot is not lost but transferred.
Kinetic Chain
The kinetic
chain is the movement of body parts. There are two types of kinetic chains,
push-like movement patterns and throw-like movement patterns. The two
categories differ in the order that joints move. Blazevich defines the movements as:
The throw-like
movement involves the progressive extension of joints, following on from each
other. This is important in:
- Increased velocity
- Force Generation
- Accuracy (2010)
A throw like movement builds upon each movementd extension and builds momentum which generates higher velocity (Blazecich, 2010). A netball goal shot, unlike a football kick down the field, does not require a large range to be achieved or a high velocity to be reached but rather an accurate action. It would therefore be less appropriate to implement a throw like motion and compromise the accuracy of the push like movement. The push like movement is commonly used to shoot for goal in netball. The flexion of the knees and elbows in the beginning of the chain movement, and the extension of the elbow and knees is the end of the chain when the ball is projected towards the target (Figure 3). When the chain is smoothly executed the accuracy of the netball goal shot can be increased.
Figure 3. Push-like movement showing simultaneous flexion and extension of the knees and elbows.
How can the Release phase help the accuracy of the
netball goal shot?
The release phase of the netball shot is important as
the ball follows the direction in which it was released by the shooter. The
release of the ball from a higher height will shorten the path in which the
ball has to travel and therefore reduces the chance of the ball being
intercepted (Blazevich, 2010).
Skill Cues
“Bend knees and elbows to generate power.”
"Push through using feet, knees, elbows."
“Simultaneously bring knees and arms up towards the
goal.”
Follow Through Phase - Backspin
What is included in the follow through phase of the netball
goal shot?
The final phase of the netball goal shot is the follow
through. In this phase the shooter must have completed the previous phases with a
degree of accuracy in order to allow a successful final phase. The final phase
requires the release of the ball while still maintaining the balance and
stability from the previous phases. Once the ball has been released the shooter
must prepare for the rebound and prepare to shoot again following the sequence
beginning from phase one.
Momentum
The goal shooter generates momentum through the kinetic chain movements. Force that is generated through the muscles and joints passes through the finger tips and generates momentum of the ball. The momentum generated by the shooter then helps prepare them for the follow through of the ball, by moving forwards.
Momentum = Mass x Velocity
The Magnus effect – Backspin
The Magnus effect is the force exerted on a spinning
object moving through air or other fluids in a direction at an angle to the
axis of spin (Blazevich, 2010). Goal shooters apply backspin to the ball when shooting
to ensure the ball drops into the ring. This
backspin on the ball is caused by The Magnus Effect. When the ball is released
from the hand with a flick of the wrist, backspin is created. When the ball
spins in the air, rotating in the opposite direction to the travel of the ball,
air travels around the ball on both sides (Figure 4). The friction between
the ball and the air causes the air to cling to the ball which forms a layer
that is referred to as the boundary layer.
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| Figure 4. The Magnus Effect (Blazevich, p.188, 2010). |
On
one side of the boundary layer, the air collides with the normal passing air-
this air decelerates - while the air on the other side moves freely with the
surrounding passing air - this does not impact the air velocity.
Therefore:
Higher air velocity = lower relative pressure.
Slower
air velocity = higher relative pressure
The pressure differential creates a Magnus force
which causes the ball to move in the direction of the difference, high to low.
Ball trajectory
Blazevich defines projectile motion as “the motion of
an object projected at an angle into the air (p. 25, 2010).” Three factors
influence the trajectory: the projection velocity, distance from the target and
release angle. These three factors will affect how high and how far the
released object will go. Netball goal shooting does not require the ball to go
far, unlike football for example, but requires higher accuracy. As there is a
target that the goal shooter is aiming for (to get the ball into the ring) the
angle of release needs to be within a certain range or the ball will miss the
target. For successful netball shooting the vertical height should be higher
which will mean the range is lower. Figure 5 from Blazevich (2010) demonstrates the impact that desired angle of release and range have on one another. Studies have shown that the optimal release
angle for netball goal shooting is approximately 60 degrees from the horizontal, although certain circumstances
can slightly vary this release angle such as distance from the ring and
defender height (Elliot and Smith, 1983 as cited in Fairley, 2014). When relatively close to the ring, the angle of release
will be greater which will cause greater vertical height and lower distance
(range) and the opposite will be required when at a greater distance from the
ring. To
improve the height that the ball reaches, the extension of the knees and elbows
should be increased. The higher height of the ball will mean that the ball will, when acted upon by
gravity (an environmental factor), fall downwards through the goal ring net,
reducing the chances of bouncing off of the ring.
Figure 5. Projection angles for netball goal shooting (Blazevich, p. 26, 2010).
Skill Cues
“Follow through with a flick of the wrist.”
"Extend shooting arm to decrease the distance between you and the goal post."
“Prepare for rebound.”
How else can we use this information?
Within the phases goal shooters must also learn to maneuver within the goal circle to become closer to the goal post to increase the chance of scoring the goal. Furthermore, constraints such as defenders, weather and personal ability (Davids, Button, Bennett, 2008) can all have an impact on a goal shooter's chance of performing an accurate goal shot. Practice with the use of constraints can benefit and improve the goal shooter's ability to over come issues they may face during a game situation.
Once the biomechanic principles are understood, the knowledge can then be transferred to analysing other sports. We discussed the ball release in the netball goal shot and described why height was more important than range. Other sports have different outcomes that require different actions to be taken. For example, the optimal ball release in the cricket bowling action would be different to the optimal ball release point in the netball goal shot. In cricket the target is lower to the ground and further away from release point, which means that the ball is going to be released lower and at a higher velocity to achieve the distance.
Other sports can be examined by using the same principles used above but in different ways. An example would be Newton's third law. The equal and opposite reaction of the ball varies between sports. In netball it is seen after the ball has been released as it rebounds off the ring. In cricket, however, it occurs at the beginning of the follow-through phase: the momentum of the body after releasing the ball.
The information that has been presented regarding the biomechanics of a successful goal shot within netball can be useful for teachers, coaches and players. The same biomechanical principles applied to determine the optimal netball goal shot can also be used to examine other sports optimal technique such as the basketball shot. Understanding the phases of the netball shot and the biomechanical principles used such as Kinetic chain, Ball trajectory, force and velocity to name a few can allow for understanding of how to create the optimal technique for any sport.
The information that has been presented regarding the biomechanics of a successful goal shot within netball can be useful for teachers, coaches and players. The same biomechanical principles applied to determine the optimal netball goal shot can also be used to examine other sports optimal technique such as the basketball shot. Understanding the phases of the netball shot and the biomechanical principles used such as Kinetic chain, Ball trajectory, force and velocity to name a few can allow for understanding of how to create the optimal technique for any sport.
Understanding the concepts of biomechanics allows for the
modification of techniques to be perfected.
