What are the optimal biomechanical principles when
performing a netball goal shot?
Katie Archer & Mel Moldenhauer
Katie Archer & Mel Moldenhauer
Major Question
Biomechanics
is the study of forces and the effects they have on living systems. It is
effected by internal and external forces. Analysing such a thing and being
familiar with the biomechanics of select movements can allow one to execute a
certain technique with precision. This also allows for further analysis of
whether there is technical error in the execution of the skill, how much the
design of the equipment effects execution and reduces risk of injury. Netball is
a very popular sport within Australia. As it is an invasion game and the main
aspect of it is to get the ball in offensive possession to then successfully
score a goal. The importance of executing a goal shot biomechanically correct
is crucial to accurately getting a goal. Biomechanics aspects also feature as a
key role in playing a successful game of netball. Within this blog we will be
discussing the biomechanical requirements of a netball goal shot and further
analysing the phases of it i.e. Preparation phase, execution phase and the
follow through.
The Answer
PREPARATION
PHASE
Balance and stability
Blazevich
(2010) states ‘the point around which all the particles of the body are evenly
distributed, and therefore the point at which we could place a single weight
vector is the body’s centre of gravity.’ All humans have a centre of gravity
which can change depending on the stance or movement of an individual, as shown
in figure 1.
Fig 1. Centre of
gravity (William, C, 2010).
In a netball
goal shot, gaining balance is the first part of the shooting sequence in order
to successfully perform the skill. If a shooter is off balance in the
preparation phase the remainder of the skill execution will likely be
unsuccessful. Efficient netballers will often have the ability to land in a
position that allows them to recover and regain balance easily (Hede, Russell
& Weatherby, 2011). Blazevich (2010) suggests that as the size of the
shooters base increases so does the level of stability. Therefore having a
strong and stable structure when goal shooting will provide balance and
stability which will increase an individual’s chances of accurately executing a
shot. Throughout the goal shot there is minimal trunk movement. If the trunk
moves during the shooting action a players stability and body balance will be
affected. Therefore a goal shooter is required to perform the action with
minimal movement of the trunk to effectively execute the shot (Steele,
1993). In addition to a stable base of support
and minimal movement of the trunk, leaning backwards with the head positioned
upright in the midline of the body will also help balance a shooting stance
(Steele, 1993).
Distance from goal
Another aspect
to consider when shooting in netball is the distance between the player and the
netball ring. This distance can have a significant impact on the accuracy of
the shot. Experienced shooters know their range and how far they can shoot
confidently (Woodlands, 2006). However many netball shooters are unaware of
their shooting capabilities at a range of distances (Steele, 1993). The further
away a player is from the ring the more likely they are to execute the shot unsuccessfully.
When the shooting distance is increased netballers are required to change the
mechanics of the shooting action, which may lose accuracy in the shot (Knusdon,
2007). As the netballer is further away from the ring they need to demonstrate
greater flexion of the knees and shooting elbow to produce more force and
increase the angle of release and the height of the projectile. There is also
more time for external factors to act upon and influence the flight of the
netball. However, if a netballer can master shooting from various distances it
will make them a more versatile player. Elliott and smith (1983; Steele 1993)
studied the optimum distance for an accurate goal shot. They discovered that
the optimum distance for a goal scoring from the post was between 0.9m to 1.5m
(3 and 5 feet). For a player to have an increased likelihood of scoring they
should position themselves between 0.9m and 1.5m from the ring. This can be
viewed in fig.
Fig. 2 Optimal distance between shooter and goal post.
EXECUTION PHASE
Forces
Newton’s law of
inertia Force can be defined as being “The product of mass and acceleration;
induces a change in the mobile state of an object” (Blazevich, 2010). The
acceleration of an object is proportional to the net force acting on it and
inversely proportional to the mass of the object (Blazevich, 2010). Thus a
change in the motion of an object requires the application of a force. Forces
are either internal or external. An internal force is within an object or
system that’s motion is being investigated such as bones or muscles. An
external force acts on an object as a result of its contact with the
environment such as friction, gravity, or contact with another object. The
major force that affects when shooting for goals in netball is the force that
is put on the balls as it travels towards the goal ring. Before the player
shoots they must be in a state of static balance holding the netball, a force
must be exerted so the inertia of the ball is changed to rest. Newton’s second
law of inertia is “The acceleration of an object is proportional to the net
force acting on it and inversely proportional to the mass of the object.”
(Arbab, 2010). Therefore the greater the mass of the object, which is a netball
in this case, the greater the force needed. The force needed when shooting is
also dependent on how far the ball needs to travel. The netball shot uses
forces of propulsion through the legs, trunk, shoulders, arms and wrists, as
you can see in Figure 2.2. At the beginning of the shot, it is required to flex
the knees to create an adequate force that will then continue the force through
to the extension phase in the shooting action which is when the ball is
propelled towards the goal ring (Steele, 1993). Technique correct shooters will
extend the knees and shooting elbow and flexed hand at wrist all in the same
motion. This simultaneous motion is used so that a high accuracy is attained
not focusing on the velocity of the shot. (Steele, 1993).
Figure 3. Velocity and time relationship in a netball
goal shot (Hede et al., 2011)
Push like movement or throw-like movement?
The
push-like movement is when the joints move at the same time, while the
throw-like movement is when one movement is completed to form another movement
to help transfer the weight (Blazevich, 2010). In the netball goal shot
he the push-like movement is required for optimal performance. It provides
prime opportunity to score as the kinetic chain forms a straight line which
follows each sequence movement. A push-like movement is also a key component when controlling the direction
of the force.
Kinetic chain/summation of forces
The kinetic chain
is a movement where all joints extend in conjunction with each other
(Blazevich, 2010). For optimal accuracy and outcomes when shooting in netball,
the push like movement allows the kinetic chain of the body to form a straight
line movement towards the goal post. Executed best when there is a stable base
of support, knees are slightly bent to form momentum, an upwards motion created
by the knees to project forward while pushing down through the toes, extending
shooting arm upwards and finally by pushing the ball in an upwards motion. The
summation of forces is the force the kinetic energy that is used through the
legs, trunks, shoulders, hand and wrist. This allows for the highest accuracy
and highest levels of force production to be achieved (Blazevich, 2010). Force
is applied through the legs, trunk, shoulders, arms and wrists through the
three phases of delivery, sequentially from the trunk, upper arm, forearm and
finally the hand. The summation of forces can be viewed in fig. 3
Fig
4. Summation of forces
Trajectory motion: height, speed & angle of release
Projectile motion
refers to the motion of an object projected at an angle into the air
(Blazevich, 2007). When attempting to go for goals in netball the angle
of release is an important aspect. Optimal angle of release includes two main
aspects which are forward and upward flight that are the results of optimal
trajectory. The optimal angle for elbow flexed is between 90 to 104 degrees
(Steele, 1993). To increase accuracy when shooting for goals, players must
create a greater flexion of the knees and bend elbows, a semi hyperextension of
the hand so the ball can be held stable, minimization of the trunk, arm and
forearm movements through the shooting action to increase hand motion, greater
release height and greater release velocity. The angle of the release changes
depending on the space the defender blocks with their hands, a higher release
of the ball would be necessary and more beneficial, while shortening the
pathway the ball is to travel (Steele, 1993). Once a projectile is released,
the horizontal of the object remains constant for the duration of its flight.
When the shot is being taken from a distance further away from the ring, more
accuracy is required, and the speed on release needs to be decreased as this
ensures the angle and height on release is more accurate (Steele, 1993).
However the projectile motion of the netball shot is an important accept when
shooting. It is the motion of an object projected at a certain angle into the
air (Blazevich, 2007). The angle of projection is a significant accept that
affects the projectile range. Objects projected vertically will land back at
its initial starting point, from the effects of gravity pushing it back down.
The angle of projection affects the range of the particular object. If the
angle of the object is greater the vertical height is increased but the range
it travels is lessened.
FOLLOW THROUGH PHASE
Magnus effect and
backspin
Netball goal shooters can improve their accuracy when executing their
shot by adding backspin to the ball. Backspin is produced by the flick of the
wrist and fingers. Backspin enhances shooting accuracy by maintaining flight
direction, bounce pattern and decreasing ball speed when contacting the ring. It
provides a higher chance of the ball rebounding off the ring to score a goal. Elite netball
players recorded completing an average backspin of 1 to 1.5 revolutions from
the release to entry of the goal (Steele, 1983).
When backspin is applied to a shot, techniques are used to cause the
projectile to spin which is known as the Magnus Effect. Blazevich (2010)
explains the Magnus effect changes the trajectory of an object towards the
direction of spin, resulting in a Magnus force.
The impact between oncoming air and the spinning object causes air on
top of the object to decrease velocity. Underneath the spinning object, the air
moves freely and therefore has an increased velocity (Blazevich, 2010). This
concept is shown in fig.5
Fig. 5 Magnus effect (Knusdon, 2007)
In relation to the netball goal shot the Magnus effect generates
backspin on the ball, creating a higher chance of the ball bouncing on the ring
and through for a goal due to its spinning direction. The netball direction
beings straight but the spin develops a sideway force that takes the ball
off-line. Due to the friction between the air and the netball, the spinning
netball grasps air particles that flows past it and these start to spin with
the ball (Blazevich, 2010). A netball goal shooter should apply a small amount
of backspin, 1 to 1.5 spins ideally, to increase the entry angle and force of
the ball to rebound in the net and not back into play (Steele, 1983).
Momentum
Momentum is an important principle in the follow through phase of a
netball goal shot. The momentum in a netball goal shot is for the player to fully
extend limbs and follow through with movement after the ball has been released.
The prior movements in the shot sequence allow energy to build up through the
legs, arms and fingers to maximise force and accuracy (Watson, 2013). When the shooter
releases the netball their arms and legs are fully extended while pushing
through the ball to release at a predetermined force and height. Once this
stage is complete shooters are ready to step towards the goal for a follow
through. The law of conservation of momentum is applied in this stage as energy
remains constant and can neither be created nor destroyed. The shooter uses
momentum gained from the goal shot to continue forward and stepping towards the
goal for a rebound.
How does this biomechanical information translate into movement?
Preparation phase
Fig 6. Preparation phase of the netball goal shot (BBC,
n.d)
In the
preparation phase of the netball goal shot the player must first receive the
ball and land on two feet. To improve accuracy of the netball shot players
should attempt to position themselves 0.9m to 1.5m from the goal post (Elliot
and Smith, 1983). The foot corresponding to the shooting side of the body must
be slightly forward or aligned with the other foot. This foot placement helps
accuracy by limiting trunk rotation and provides a stable base of support. A
players hips need to be level and the whole body must be parallel facing the ring.
Feet should be placed shoulder width apart or less to increase core stability
and ensure the centre of mass is above the base of support to provide optimum
stability (Watson, 2013). This prevents players breaking the stepping rule in
netball and creating a turnover. The knees should also be slightly bent. When
bending the knees a player’s centre of gravity is lowered further assisting the
base of support. The trunk should be in an upright position, slightly learning
backwards with their head upright in the centre of the body to help balance the
shooting sequence. The ball should be held steady in the players
preferred hand with fingers slightly spread to ensure there is no gap between
the ball and fingers. The players second hand should also be placed on the ball
to develop balance, support and control for the shot. The ball should not be in
the players sight as it is held above their head, slightly backwards with
elbows somewhat bent. A very important concept for players to remember during
this phase is to minimise head and trunk movement as this will ensure stability
and balance throughout the entire movement.
Execution phase
Fig. 7.
Execution phase of the netball goal (BBC, n.d)
This is the stage where the power for the goal shot
is produced. The power for the goal shot is produced from the knees. The player
must maintain a stable base ensuring their able to keep their whole body
balanced, while focusing on the goal ring. In many sports it is important to
keep the head and eyes still during the execution of the movement (Blazevich,
2010). Elbows will be flexed so that the ball is positioned behind their head.
As the elbow bends, the ball is levered backwards while the elbows remain above
head height. The next movement is using their ankles and knees to push through
the ground and the push arms into a straight position. Ball is released at the
height of the arm extension which should occur once legs and arms are
straightened sequentially. Optimal shot for goal would be released at an angle
of approximately 60degrees, with a backward spin of 1 to 1.5 revolutions in
relation to its direction of travel. Implications: Aspects of the goal shot
that improve the technique and accuracy are ensuring the extension of the
shooting hand isn’t over extended, hypertension of the hand needs to be avoided
as it affects the wrist, and minimal movement of the trunk and forearm is
beneficial towards the shooting motion. To improve the accuracy of the netball
shot the player should use backspin to assist the flight direction. This also
reduces the speed of the ball when it hits the goal ring which will give it
more opportunity to fall into the net. Having a flexible wrist is important as
it will mean creating backspin on the found that the most preferable distance
was between 0.9m and 1.5m from the post. The release height of the ball can be
increased by extending the knees further and the extension at the elbows of the
shooting arm is full. The closer they are, the more accurate they are likely to
be. A study by Elliot and Smith (1983).
Follow Through Phase
Fig. 8. Follow through phase of the netball goal shot (BBC, n.d)
The final phase is the Follow Through phase. The
last 2 steps need to be successfully completed for this final stage of
following through to happen. After the release of the ball, it’s important for
player to remain upright and balanced and then following the ball in to prepare
for the possibility of a rebound and positioning themselves where they would
most likely get the rebound.
The above
information allows us to thoroughly understand the optimal biomechanical
principles of a netball goal shot. This information can be used among coaches,
teachers and players to improve technique and accuracy when performing the
netball goal shot and promote optimal performance. Understanding biomechanical
principles of an action can help individuals improve their overall performance
and become versatile players in a game. These biomechanical principles will
help to produce highly skilled players and also act as a safety precaution to
prevent players executing the skill incorrect and injuring themselves. The
biomechanical principles of the netball goal shot can also be used for other
shots in netball. Knowledge of the kinetic chain can help players decide which
pass to use. For example, if a player is struggling with force for the shot
they can adopt a push-like pattern in order to produce enough acceleration to
power the pass. However for stronger players a throw-like movement may be used.
Understanding which movement pattern to use can be particularly helpful when
teaching children and adults.
The
biomechanical principles of a netball goal shot are also evident in sports
where accuracy is vital to the game. Many of the biomechanical principles in
the netball goal shot can be transferred into a game of basketball when
shooting. These include balance, force, kinetic chain, summation of forces,
Magnus effect, backspin, momentum and projectile motion. In relation to
cricket, the biomechanical principle of trajectory motion can be used. Netball
goal shooters must be aware of their trajectory motion as do bowlers in sports.
In both cricket and baseball a bowler’s main aim is to bowl/throw the ball at a
correct projectile motion and force to ensure that the opposition player experiences
difficulty upon returning the ball. This
trajectory motion can also be used when executing a throw in cricket. However
the difference between a netball shot and cricket throw is the distance of the
shots. From analysing force we can determine that if an object is projected
vertically it will land back at its starting point due to gravity. This helps crickets understand the trajectory
requirements of the throw and find a projectile angle that will ensure the
throw is accurate. For a long throw players should find a projectile angle that
has equal magnitude of vertical and horizontal velocity which will therefore
increases the range of the throw.
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principles must be applied to best perform a goal shot in
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