Jessica
Kneebone 2096334
Introduction
Netball
is enjoyed by one of the largest number of players of any team game within the
commonwealth (Knusdon, 2007). Despite this fact, there is a lack of published
literature that analyses skill and each movement within the game. However some biomechanical research has been
conducted and this blog with explore these principles in detail for the netball
goal shot. In relation to the game of netball, accurate shooting is critical to
the success of the netball team. To answer this question properly we first need
to identify and understand the biomechanics of this activity. Biomechanics is
the sport science field that applies the laws of mechanics and physics to human
performance, in order to gain greater understand of performance in athletic
events through modelling, simulation and measurement (Blazevich, 2010). So the
question is what biomechanical principles must be applied to best perform an
accurate goal shot in netball?
The
Answer
Preparation
Phase:
Preparation Stance
To prepare for an accurate netball shot the correct stance must be
taken. Excessive trunk movement before or during the shooting action could
hinder with stability and body balance. (Steele, 1993). Having a solid
structure for balance and stability will allow for optimal performance to execute
an accurate shot at goal. A key skill that many athletes must be able to maintain
is the skill of balance and stability. The base of support is the area by which
the body is supported. The larger the area of base support is, the greater the
stability (Hede, Russell & Weatherby, 2011). As shown in Figure 1.1 , you
can see a low centre of gravity above the base of support improves stability.
Figure
1.1 ( Hede et al., 2011, p. 7)
When shooting a goal in netball often the athlete is in a static position meaning when the body is at rest (Blazevich, 2007). However, a body may be stable in one direction but not in another therefore, it is critical to consider the orientation of the base support to the force being applied. Relating this to a netball shot there is not much force needed to shoot the netball the athlete will only have their feet shoulders width apart therefore creating a more stable base and centre of gravity (Hede et al., 2011). A study that was completed by Elliot and Smith (1983) found that skilled netball shooters also maintained a relatively upright trunk position, leaning backwards slightly with their head upright and cantered in the midline of the body to help a balanced shooting stance.
How Close to Stand to the Ring
Distance
Another
aspect that contributes to an accurate netball shot is the distance the player
is from the netball ring. Often netball players are aware of their shooting
percentages over different distance ranges (Steele, 1993). The further the
distance the player is to the ring obviously the chance of achieving a goal is
reduced and it requires greater flexion of the knees and shooting elbow to
create more force while also increasing release height and greater velocity
(Steele, 1993). Shooting goals further from the post required changes in the
mechanics of the shooting action. These technique changes may account for the
loss of accuracy especially in the longer shots (Knusdon, 2007).
Projectile motion
The
projectile motion of the netball shot also plays a vital role in completing an
accurate netball shot. Projectile motion refers to the motion of an object
projected at an angle into the air (Blazevich, 2007). If an object is projected
vertically, it will land back as its starting point this is due to gravity pulling
it back to earth. The maximal range of projectile is determined partly by its
angle of projection, when the angle is greater the object attains a great
vertical height but lesser range (Blazevich, 2007). The release of the netball
would slightly be above 45 degrees and between 70 degrees however, it also
depends on the height of the defender as it can affect the angle of release. Blazevich
(2010) notes that “At a projection angle of 45 degrees, the object will have an
equal of vertical and horizontal velocity and its range will be maximised.”
This relates back to the principle of gravity, and must be taken into account to
release the ball at an angle that allows it to travel horizontally towards the
ring but also vertically upwards. When an object is projected through the air
at an angle, it is called projectile motion. When the ball is released the trajectory of
a ball is influenced by projection speed, the projection angle and the height.
Execution
Phase:
Does the Push-Like Movement or
Throw-Like Movement Pattern Provide a More Accurate Netball Shot?
To answer this question the push-like movement pattern is used to throw
the netball into a goal ring. This is a movement that replicates the motion of
pushing something and where all joints extend in conjunction with each other
(Blazevich, 2010). The push-like movement often provides optimal outcomes in
netball goal shooting because it allows the kinetic chain of the body to create
a straight-line movement. This kinetic chain results in the forces being put
into movement but also increases the accuracy by ensuring that all parts of the
kinetic chain are aimed towards the goal.
The process broken down can be seen as;
- Stable base of support
- Slight bend in knees to build momentum
- Upwards motion using knees to project forward while pushing up on toes
- Extend shooting arm upwards
- Push ball off tips of fingers in an upwards movement
The process broken down can be seen as;
- Stable base of support
- Slight bend in knees to build momentum
- Upwards motion using knees to project forward while pushing up on toes
- Extend shooting arm upwards
- Push ball off tips of fingers in an upwards movement
This sequence allows the energy to build up throughout all the joints being used in a way that maximises both force and accuracy as seen in Figure 2.1. Despite the beneficial elements of this approach, one major disadvantage of the push-like pattern is the slow movement speed; this speed may provide the opposing team with a chance to intercept the ball while it is in flight. The throw-like pattern provides more force and speed behind the object (the netball) but follows a curved pattern and therefore reduces the accuracy of the shot (Blazevich, 2010)
Figure 2.1 (Teach
PE, 2013)
Taking the shot:
Force
Force is defined as being “The
product of mass and acceleration; induces a change in the mobile state of an
object” (Blazevich, 2010). When a player is in a state of static balance with
the netball in hand, force must be exerted in order to change the inertia of
the ball to the state of rest. Newton’s second law is just this, “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). Newton’s
second law would say that the greater the mass of a netball, the more force
that must act upon it and the force that must be applied to the netball when
shooting is dependent on the distance in which the ball must travel. The
previously discussed push-like movement patters is a key component of
controlling the direction of the force being applied during a netball goal
shot. Having one hand pushing the ball and the other hand as the guide also
maximises the force of the motion whilst maintaining accuracy (McGinnis,
1954). Forces can
specifically be defined as a push or pull or anything that causes or has
potential to cause movement (McGinnis, 1954). Forces can also be described as
internal, act within the object or system or external, act on an object as a
result of its interaction with the environment (McGinnis, 1954). For Example
muscles and bones are seen as inside the system therefore, are internal forces,
and forces applied outside the body such as gravity, contact with the ground or
another person are all external forces. When
shooting in netball, the ball is propelled through legs, trunk, shoulders,
arms, and wrist, this is demonstrated in Figure 2.2. Many shooters tend to bend their knees during
the sinking action of the shot. 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). 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).
Figure 2.2 ( Hede et al., 2011)
Ball Release
The
ball release is an important concept when performing a shot for goal. The trunk
of the body is straight and an upright head position is maintained. Skilled shooters release the ball with arm
extended, but not to the position of being rigid or unbendable. The release
point of the ball is directly above the head. This is evident is accurate
shooters. When a defender is present the angle of release will change if the
defenders hands are close hence an interception or tip may be achieved. A high
release of the ball was recognized as beneficial which saw the ball release
from the hands higher, also shortening the pathway the ball travelling to reach
the goal ring (Steele, 1993). Release
height can be influenced and improved by extension at the knees and at the
elbow of the shooting arm (Steele, 1993).
Follow
Through:
Back spin
Average
elite netball players were recorded completing backspin of 1 to 1.5 revolutions
from the release to entry of goal (Steele, 1983). Backspin is found to improve
accuracy by supporting and maintaining flight direction and decrease ball speed
when coming into impact with the goal ring. This back spin then leads to the
ball to rebounding off the ring and through for a scored goal. Also numerous elite shooters are quite tall
in structure and less muscular therefore causing them to have stronger knees
and elbows as these muscles are consistently being used.
Magnus effect
The Magnus effect is a
change in the trajectory of an object towards the direction of spin, therefore
resulting in a Magnus force (lift force acting on a spinning object) (Blazevich,
2010). It can be explained that a spinning ball, in this instance the 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).
Figure 3.1: (Knusdon, 2007).
In Figure 3.1 the collision
between the oncoming air and the ball or air spinning with it causes air on one
side of the ball to slow down (decreased velocity) is demonstrated. On the
other side the air moves past unobstructed (Blazevich, 2010). In netball and
basketball backspin of the ball increases the chance of bouncing on the ring
and dropping through the net (Knusdon, 2007).
This is due to the spinning ball bounces in the direction of the spin on the
ball and putting backspin on the ball, the ball will bounce backwards and an
accurate goal shot will have been performed (Knusdon, 2007).
How Can we Apply This
Information
We see this shooting technique in many other sports. In
basketball, and other throwing games that accuracy has a vital impact on the
success of the game. From the biomechanical principles such as balance,
summation of forces, Magnus effect and projectile motion information can be
utilised to improve performance in other sports. For example in cricket the
bowler’s main aim to is bowl the ball with the correct angle of release, height
of release and enough force to get the batter out.
This information can also be used in different
mediums. For example a school setting when teaching the basics of a netball
shot becomes relevant. Applying the above information
to coaching and teaching settings the players will successfully be instructed
to execute the skill to their optimum ability (Steele, 1993). It is ideal for junior players to be taught
the theoretical background of a skill, as this will allow for they to achieve optimal
technical performance during a game (Steele, 1983).
After
investigating these biomechanics principles in the context of netball shooting,
it can be said that the quality of game can be greatly increased by taking
these factors into consideration.
References
Arbab,
A. I. (2010). The generalized newton's law of gravitation. Astrophysics and
Space Science, 325(1), 37-40.
Blazevich, A. (2007). Sports
biomechanics the basics: Optimising human performance. Bloomsbury Black
Publishing.
Hede,
C., Russell, K., & Weatherby, R. ( 2011) Applying biomechanics to sport(3rd
ed). New York: University of Oxford.
Human
Kinetics (n.d). Magnus Effect Human Kinetics. Retrieved 16th June 2014 from: http://www.humankinetics.com/excerpts/magnus-effect
Knusdon,
D. ( 2007). Fundamentals of biomechanics:
Department of Kinesiology. California
Springer Publishing. 2, 4-334.
McGinnis, P.
M. (1954). Biomechanics of sport and
exercise. (2)5. Champaign, IL: Human Kinetics, 5-9
Steele,
J. ( 1993). Biomechanical factors
affecting performance in netball. Department of Biomedical Science. 3, 1-18.
Teach
PE. (2013). Netball Coaching. Retrieved from Teach PE: http://www.teachpe.com/netball/rules.php
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