Biomechanics is a field of science devoted to
understanding mechanical principles in relation to biological organisms
(Blazevich, 2012). The netball shot is understood in different stages when
referring to the biomechanical movements. The biomechanical principles of the shooting action are, balance
and stability, ball release, ball trajectory, distance from the goal post,
backspin, magnus
effect and netball shot sequence (Seelander,
2013). A netball goal can only be improved through identifying these
processes which must be taken and also identify biomechanically how the body
must propel and follow through when shooting a goal. The following discussion
will explain the biomechanical phases that must be conducted to ensure a
successful goal.
There are three main movement phases when conducting the netball shot at
goal. These three phases are preparation, execution and follow through.
Preparation phase:
The preparation phase contains all of the movements that prepare an
athlete for the performance of the skill (Pyke, 2010). When conducting the
netball shot the preparation phase focuses on the stance of the player before
executing the movement. A player’s balance, position, concentration and aim are
all aspects within this phase, which can influence the movement and the outcome
(successfully shooting the goal or missing). A player must find their centre of
mass, in order to have balance when preparing for the goal. This is done by
identifying the point at which the mass of the body is evenly distributed in
all directions (Blazevich, 2012), in this case it is the players feet being
positioned shoulder width apart. The player’s stability is found by identifying
the body’s base of support. The larger the area of
base support, the greater the stability. However the center of gravity and mass
can change depending on the angle or stance of an athlete,
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| Centre of gravity |
as well as position. When shooting a goal in netball often the athlete
is in a static position meaning when the body is at rest (Blazevich, 2012). As
the motion of shooting a netball does not require a high level of force a
netballer stands with feet shoulder width apart with an upright trunk position,
slightly leaning backwards with their head upright and cantered in the midline
of the body to help a balanced shooting stance (Moon, 2013). This allows a player to evenly space
their feet under their trunk without breaking the rule of stepping in the game
of netball. A shooter standing with their two feet placed on the ground,
shoulder width apart increases the core stability of the player and keeps the
centre of mass above the base of support - giving optimum stability (Watson,
2013). Excessive trunk movement during the shooting action could hinder with
stability and body balance; therefore, there is minimal movement of the trunk
and arm sequence (Steele, 1993). However a shooter is able to reduce their stability of their
base support by stepping forward (balancing on one leg), to provide a closer
shot at goals. This process goes against biomechanical principles but is
sometimes beneficial in a real life game situation
Execution phase:
The execution phase is the performance of the actual movement that often
includes a point of contact with an object (e.g., contact of the baseball bat
and ball), the release of an object (e.g. shooting a netball) or a flight phase
(e.g., long jump) (Pyke, 2010). Shooting a goal in netball relates to the
release stage after the preparation. This stage is broken down into two main
parts, the shooting action and the release of the ball. The shooting action
includes the focus of the eyes, which helps to maintain balance and stability
and creates a focal point. The eyes must always be focused on the top of the
goal ring to define a point in which the body motion must push towards.
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| Summation of force |
The shooting action phase is broken down into the movement of the elbow,
knee flexion and extension performed before releasing the ball. A goal shooter
in netball propels the ball through their legs, trunk, shoulders, arms, and
wrist (Seelander, 2013). The action of shooting a netball replicates the
pushing motion, which allows all joints to extend in conjunction with each
other (Blazevich, 2012). By shooting the netball it is using force (push,
pull). The push force has four main areas; main flexing or sinking at the knees
is required to ensure adequate force could be created during the extension
phase of the shooting action to propel the ball to the goal ring (Steele,
1993). The push-like movement often provides optimal outcomes in netball goal
shooting as it allows the kinetic chain of the body to create a straight-line
movement (Watson, 2013). The push-like movement can be used to improve force
production and accuracy (Blazevich, 2012). The optimal angle for elbow flexed
stated in Biomechanics factors affecting performance in netball (Steele, 1993)
was 90 to 104 degrees. By flexing the elbow between these degrees the accuracy
and force is increased. Newton’s 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).
Once these movements are complete the second stage is introduced which
is the release stage. This stage focuses on the wrist flick and the extension
and transfer of kinetic energy to the ball (Seelander, 2013) quick and continuous.
When a sequence of movement is undertaken to produce an optimal
velocity, then each segment is moved the instant that the previous segment
begins to slow down, this is known as the summation of forces (Hodgson, Wilson
and McNaughton, 2011). To obtain maximum force, or
little force it is necessary to combine or add up the forces applied by
different body parts (Blazevich, 2012). This concept is known as the summation
of force. Figure 1 demonstrates this by showing the sequence in which a
netball player’s body moves when shooting a goal.
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| Figure 1 |
The release point of the ball is directly above the head. A netball
shooter must also take into account gravity and project the ball at an angle
that allows it to travel horizontally towards the ring but also vertically
upwards (Watson, 2013). Through doing this, the netball is likely to be pulled
down by gravity into the net, apposed to not projecting enough height on the
ball and having the netball fall short of the ring.
In many sports it is important to keep the head and eyes still during
the execution of the movement (Blazevich, 2012). This is particularly important
within netball to ensure that your trunk and limbs don’t move off to the side
when performing the shooting action. Magnitude, direction, a point of
application and a line of action are all common properties, which impact the
force applied to the ball when shooting.
Skilled shooters extend the knees and shooting elbow and flexed hand at
wrist in the same motion. This simultaneous motion is used to attain utmost accuracy
rather than maximum velocity (speed) for the shot (Steele, 1993). The two
phases within the execution stage are often hard to teach and put together
smoothly due to the motion being simultaneous.
Follow through phase:
Finally, the follow-through refers to all of the movements that occur
after the release of the ball. This stage focuses on the momentum of the
player. As a player releases the netball they push through the ball and extend
both arms and legs fully to release the ball at the correct height and force.
The momentum of the player is to extend all limbs and following through with
the movement still after the ball has been released from a players hands. The sequence
of the ball release allows the energy to build up throughout all the joints
being used (legs, arms and fingers) in a way that maximizes both force and
accuracy (Watson, 2013). Shooting a netball focuses
more on accuracy; therefore netballers decrease the release speed placing more
emphasis on perfecting the angle and height of release (Blazevich, 2007). This
is known as the Magnus effect, which occurs when a spinning object is moving
through air or water (Blazevich, 2012). The netball starts off straight
but the spin creates a sideways lift force that takes the ball off-line. This means a spinning netball ‘grabs’ the air that flows
past it because of the friction between the air and the ball, so these air
particles start to spin with the ball (Blazevich, 2010). Trained netball
shooters apply a small amount of backspin to allow the netball to increases the
entry angle resulting in a goal. This is done due to the backspin forcing the
ball to bounce into the net rather then back to the player.
Once this stage is complete a shooters arms and legs are left straight
and ready to step towards the goal. Energy can neither be created nor destroyed
but remains constant (the law of conservation of momentum), which means a
player uses the momentum of the shooting action to continue forward, by
stepping towards the goal for the rebound (Blazevich, 2012).
Distance from the goal
ring:
The distance from the goal ring affects the accuracy of
the goal shot. Therefore this means that the further away from the goal post
and the angle the goal shooter is standing on influences the force, magnus
effect and projectile of the ball; resulting in a lower chance of successfully
shooting the goal. Gravity influences the distance the ball is projected from,
as the further away from the goal, the ball is released the greater impact
gravity has on pulling the ball down (dropping before the goal ring). Greater
flexion of the knees and shooting elbow create more force while also increasing
release height and greater velocity (Steele, 1993). This is required when
shooting a netball from a further distance in the goal ring.
Answer:
But how can a biomechanical break down of each phase, help
to improve the accuracy of a netball shot?
Biomechanical information can be used to refine the existing
techniques of experienced netball players so they may achieve optimal technical
performance of game skills while minimising the potential for injury (Steele,
1990). By creating an
understanding of biomechanical concepts such as balance and stability, gravity,
centre of mass, magnus effect, projectile motion,
summation of force Newton’s second law and the kinetic chain, a player is able
to identify the correct stance, height and angle to release the ball. This
creates a greater chance of scoring a goal.
‘To improve shooting accuracy players should demonstrate
greater flexion of the knees and shooting elbow when preparing to shoot,
sufficient but not excessive hyperextension of the hand to stabilize the ball, minimization
of trunk, arm and forearm movements during the shooting action in favour of
increased hand motion, greater release height and greater release velocity
(Steele, 1990)’. 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’. Constraints such as defenders, weather and personal ability (Davids,
Button, Bennett, 2008) all impact on a goal shooters chance of performing an
accurate goal shot. Practice with constraints taken into account will help to
improve a goalies ability to over come issues they may face during a game
situation.
Successful execution and accuracy requires the athlete to apply the
correct amount of force, in the correct direction and with precision timing (Pyke,
2010). It is recommended that athletes should use
backspin to support the flight direction, this will reduce the ball speed
impact with the goal ring and provides better opportunity for the ball to
rebound off the ring and into the net. Keeping a stable stance by having feet
shoulder width apart and moving one foot slightly forward (within the netball
rules of stepping) will provide a larger centre of mass resulting in balance
and less trunk movement during the netball shot.
Movement phases of the netball shot:
 |
| http://www.quintic.com/education/case_studies/Equations_of_Motion.htm The main elements to emphasis on through out the netball shot progression to improve accuracy are: |
- Centre of gravity is centre to mass (person is balanced and stable)
- Flexion of the elbow as ball it placed behind head
- Flexion of the knees to produce a force on the ball
- Simultaneous flexion of both knees and elbow in same motion
- The angle of release
- Extension of the knees and elbows to produce force on the ball
- Right arm is fully extended
- Backspin is placed on the ball by flicking of the hand and fingers
- The flight of the ball is vertical and then drops down due to gravity (Seelander, 2013).
Conclusively biomechanical principles such as balance,
summation of forces, Magnus effect and projectile motion can be used to improve
performance in other sports, which use the push shooting action.
Reference List:
Blazevich, A. (2012). Sports biomechanics the basics optimizing human
performance. Torque and centre of mass (pp.
62-71) Great Britain
Blazevich, A. (2010). Sports biomechanics the basics optimizing human performance. Torque and centre of mass (pp. 24-29) Great Britain
Blazevich, A. (2007). Sports biomechanics the basics optimizing human performance. Torque and centre of mass (pp. 104) Great Britain
Hodgson, C. Wilson, A. McNaughton, N. (2011). Physical education Sace 2 workbook.
Skill Acquisition and the Biomechanics of
movement. Chapters 5-8, accessed 10/4/14
Pyke, F. (2012). Methods of movement analysis. Human Kintetics. Retrieved from, http://www.humankinetics.com/excerpts/excerpts/methods-of-movement-analysis
Seelander, K. (2013). Biomechanics
of a netball shot. Retrieved from, http://kimberleyjs.blogspot.com.au
Steele, J. R. (1990). Biomechanical factors affecting performance in netball. Sports Medicine, 10(2), 88-102.
Watson, M. (2013). What biomechanics principles must be applied
to best perform a goal shot in netball. Retrieved from http://madeleinewatson-biomechanics.blogspot.com.au
