The purpose of this blog is to explore the biomechanics of the netball shot in order to determine the most optimal technique for shooting with accuracy. The biomechanical principles will be discussed within each skill phase, including the preparation phase, force production phase, release phase and the follow through. The following video clip provides a demonstration of the basic shooting technique used in netball.
Video Clip: Demonstration of the shooting technique in netball.
Preparation phase
The preparation
phase is the most important phase to execute correctly, as it will ultimately
determine the accuracy of the shot. Steele (1990) suggests that shooters should
allocate at least 50% of their possession time preparing for the shot. During this phase it is integral that shooters are stable and balanced by maintaining their center of gravity in preparation for the
shot. Blazevich (2010, p.63) defines center of gravity as the, “point around which all particles of the body
are evenly distributed, and therefore the point at which we could place a
single weight vector, is the body’s center of gravity”. In order to achieve
balance, a goal shooter must locate their center of gravity over a stable base
of support, which in netball involves positioning the feet shoulder width apart
(as shown in figure 1). If a shooter leans too far forward or backwards,
their center of gravity would shift outside their base of support, resulting in
instability and poor accuracy. Elliot and Smith (1983) also found that to
maintain stability, goal shooters must minimise head and trunk movement.
Shooters can accomplish this by aligning their feet and body to the goal post.
This will enable the shooter to produce a concentric force, which will result in the
ball following the direct path in which the force is applied (shown in
figure 2) (McGinnus, 2013). During the preparation
phase the shooters body and the ball remains unchanged, hence
demonstrating Newton’s First Law of motion which states, “An object will remain at rest or continue to
move at a constant velocity as long as the net force equals zero” (Blazevich,
p.45, 2010). The shooter and the ball will remain in a state of inertia until
the commencement of the following skill phase.
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| Figure 1: Shooter with stable base of support. |
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| Figure 2: Concentric/Eccentric Force |
Force
Production phase
The force
production phase is consistent with Newton’s Second Law of motion
which states, “the acceleration of an
object is proportional to the net force acting upon it and inversely
proportional to the mass of the object” (Blazevich, p.45, 2008). For the
ball to propel into the air, towards the goal ring, shooters must produce an
accurate amount of force. Within a game, the amount of force will
vary depending on the goal shooters position within the circle. During the
force production phase, shooters execute a push-like pattern of
limb movements. Blazevich (2010, p.296) describes a push-like pattern the “simultaneous movement of joints in our
kinetic chain in one single movement”. This is evident in netball when the
shooter flexes their knees and elbows and extends them together, in one movement, to produce
force behind the ball. The angle between the knees and elbows at this stage of
the skill will influence the amount of force produced. In their study, Elliot and Smith (1983) found
that the angle between the shooters thigh and calf during flexion varied
considerably, however averaged at about 112.6 degrees. This study also demonstrated
that there was less variation in the angle of the shooters elbows during
flexion, with the optimal angle relative to 104 degrees. Delextrat and Sampson
(2010) found that the joint angles adopted during the shooting action determines
the position of the ball at the point of release, which they consider to be the
most important factor for success. If shooters need to produce more force, they
should decrease the angle between their thigh and calf, rather than decreasing
the angle of the elbows. If shooters bring the ball back too far behind their
head, they risk the ball overshooting the goal ring. This can be attributed to impulse-momentum relationship, which describes how the momentum
of an object changes in proportion to the sum of applied impulses (Blazevich,
2010). Therefore, by increasing the flexion of the elbow, the shooter is
applying more force over a longer period of time, resulting in more angular
momentum. Acquiring this understanding is essential for shooting accuracy as it
demonstrates how shooters should produce more force if they are further away
from the goal ring.
Release Phase
The force that
was produced in the previous phase is used to propel the ball into the air,
towards the goal ring. There are 3 key elements that influence the flight
trajectory of the ball after release including, projection speed,
projection angle and the height of projection. In sports like
javelin and shotput the aim is to achieve the greatest distance
of an object before it falls back down to the ground. The distance covered is
the outcome of the speed of which the object was projected. For the netball
goal shot, the aim is to shoot for accuracy rather than distance. In saying
this, without some projection speed, the ball would fail to travel the distance
between the shooters hands and the goal ring. The shooter remains In a
stationary position while executing the shot, hence the projection speed of the
ball immediately after release is the result of the angular velocity produced
by the knees and elbows during the force production phase. More importantly, is
the angle of which the ball is released. A shooter can
throw the ball between 0 and 90 degrees (right angle). The angle of release is ultimately determined by
the angle between the upper arm and forearm at release point. In order to
produce force behind the ball the shooter must extend (increase the angle) of
their knees and elbows, however not to the point of being stiff or locked (as shown in figure 3) (Steele, 1993). Elliot and Smith (1983) found that the most accurate shots were
achieved when the ball was released directly above the head at an angle of 60
degrees. In order for the ball to ‘swish’, the ball should pass through the ring at
45 degrees. To achieve this the ball must reach enough vertical velocity during flight. When vertical velocity is
greater, the range of distance covered by the ball is less (Blazevich, 2010). Therefore,
more vertical projection would need to be achieved for shots taken further away
from the goal ring. The height of projection also has a major influence on
shooting accuracy. At the end of this phase shooters must be on their toes to
maximise the height at which the ball is released. Hudson (1982) found that
shooters' who released the ball at a greater height, achieved greater accuracy
in their shots. By heightening the release point, shooters are
effectively shortening the path that the ball has to travel to reach the goal
ring (Steele, 1993). This contributes greatly to shooting accuracy as there is
less time for external factors to affect the balls trajectory during flight
(eg. wind). It is also important to note that the principles of balance and
stability are critical during this phase.
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| Figure 3: GS just before the ball is released. Her knees and elbows aren't stiff or locked out. |
Follow
Through Phase
During the
follow through phase the shooter executes a wrist flick as the ball leaves
their finger pads. By doing this, the shooter imparts torque (moment of
force) on the ball, which Blazevich (2008, p.63) describes as, “the magnitude of force causing the rotation
of an object”. The influence that backspin has on shooting accuracy can be
explained through the Magnus Effect, which pursues
that a ‘lift force’ is produced on
the ball as air particles (moving at a faster rate) collide with the balls
surface, which in turn exerts more pressure, forcing the ball into a backwards
spin (Knudson, 2003). Figure 4, shows the Magnus Force inflicted
on the ball as the air separates the balls boundary layer. Blazevich (2010, p.190) argues that since the masses of air change
the balls velocity (both magnitude and direction), a force must have been
applied. This force is relative to masses of air colliding with the ball during
flight. As shown in figure 4, the boundary layer at the bottom of the ball
separates later than the boundary layer at the top of the ball. Thus a mass of
air with velocity moves upwards behind the ball, resulting in a ‘lift force’ (Blazevich, 2010). This
impact of air masses on the balls velocity is coherent with Newton’s Third Law- For every action, there is
an equal and opposite reaction (Blazevich, 2008). In netball shooters can
use backspin to maintain the balls direction of flight and to reduce ball speed
on impact with the goal ring (Elliot & Smith, 1983). This in turn increases
the chance of the ball rebounding off the ring and into the net. Elliot and
Smith (1983) found that the most accurate shooters imparted backspin of 1 to
1.5 revolutions in its direction of travel. A similar study (Delextrat &
Sampson, 2010) showed that backspin was also beneficial in relation to the
release angle in which the ball entered the ring, which was due to the balls
increased velocity during flight.
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| Figure 4: Magnus Effect- Air masses colliding with balls surface during flight, resulting in backspin. |
After conducting
a biomechanical analysis of the netball goal shot, the most optimal technique has been discovered. To achieve accuracy, the goal shooter must
execute each skill phase correctly. During the preparation phase, shooters must
align their center of gravity over a stable base of support, which can be achieved by setting their feet shoulder width apart and in
alignment with the goal ring. This will enable the shooter to produce a concentric
(straight) force, as they are effectively minimising trunk and head movement during the shot. This supports that shooters’ should compose themselves, and set up
into the appropriate stance, which will allow them to maintain balance and stability
during the execution of the shot. In order to propel the ball into the air, the
shooter must produce enough force through the flexion of their knees and elbows. However,
shooters should avoid flexing their elbows too far as they will produce too
much angular momentum, which would most likely result in the ball overshooting
the ring. This was explained through the impulse-momentum relationship, whereby
more force is exerted over a longer period of time. To further improve accuracy
shooters need to be aware of the projection angle and speed of which the ball is
released. Elliot and Smith (1983) support that the release angle for an optimum
shot is 60 degrees. It was outlined that when vertical velocity is more, the
distance covered will be less. Hence, shooters need to apply different
magnitudes of force depending on their position in the goal circle. At release
point, the shooters arms and knees should be fully extended, however not to the
point of being locked out. The height of
release contributes greatly to the accuracy of the shot as it effectively
reduces the balls flight time. For this reason, shooters should release the
ball at the highest point, which is directly above the head with arms fully extended. The follow through is essential as this is the point at which the shooter imparts backspin on the
ball. The Magnus Effect ultimately results in the ball achieving greater
velocity, enabling it to fall through the goal ring at 45 degrees. Backspin is
also important is it slows the speed of the ball down and increases the chance
of it falling into the ring after a rebound. All of these elements are
essential if goal shooters want to shoot for accuracy.
How can this information be used?
Understanding
the biomechanics of movement is integral for improving athletic performance. The
biomechanical principles that have been discussed throughout this blog can be
applied to several sports. Similar biomechanics are observed during the
basketball free throw, especially in terms of force, angular momentum, center
of gravity and the Magnus Effect. Angular kinetics can be used to improve
sprinters’ running technique. In particular the impulse-momentum relationship
explains that if sprinters make more contact with the ground, they will be able
to produce a greater amount of force over a longer period of time. This
knowledge is particularly valuable for any sports involving explosive
movements. The Magnus Effect can also be used to explain why a golf ball curves
during flight. Golfers can use this knowledge to change the direction of their
swing and in turn improve the accuracy of their shot. This same principle applies to soccer players when they kick a curve ball to bypass the goal defender.
References
Blazevick, A.J. (2010). Sports
Biomechanics: The Basics: Optimising Human Performance, A & C Black,
London.
Elliott, B., & Smith, J. (1983). The relationship of
selected biomechanic and anthropometric measures to accuracy in netball
shooting. Journal of Human Movement Studies, 9(4), 171-187.
Delextrat, A., & Goss-Sampson, M. (2010). Kinematic
analysis of netball goal shooting: A comparison of junior and senior players. Journal
of sports sciences, 28(12), 1299-1307.
Hudson, J. L. (1982). A biomechanical analysis by skill
level of free throw shooting in basketball. Biomechanics in sports,
95-102.
Knudson, D. (2007). Fundamentals of biomechanics.
Springer Science & Business Media.
McGinnis, P. M. (2013). Biomechanics of sport and
exercise. Human Kinetics.
Steele, J. R. (1990). Biomechanical factors affecting
performance in netball. Sports Medicine, 10(2), 88-102.
YouTube, Netball
Skills: Basic Shot Technique [video], retrieved from https://www.youtube.com/watch?v=wGUXLyYXvzU.
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