THE QUESTION…

INTRODUCTION:

Within the sport netball, most would say that the most crucial position to play is that of a goal shooter/goal attack. As these players are relied upon by the team, to score points within the game, by successfully making a shot with the ball into the hoop. Netball is a sport enjoyed by a large amount of participants of any team within the Commonwealth, especially Australia, New Zealand and the United Kingdom (Steele, 1990). The sport is loved for is fast passed invasive nature, of trying to take and maintain possession as a means to eventually score, through the use of a team approach, utilizing various positions of different players on the court. Seeing as goal shooting is the most relied upon as a means to win, within the game, the biomechanical principals utilized to perform the shot will be further examined.

Figure 1. (IntoSport, 2011)
Video demonstrating how to perform basic netball shot, with appropriate skill cues.

By understanding the biomechanical principles involved in generating an accurate and successful netball goal shot, a player might be able to further develop their understanding of the skill. Biomechanics has been defined as the study of movement of living things using the science of mechanics (Hatze, 1974). So the question now is, what are the biomechanical principles to generate a successful netball goal shot? The answer to this question will be discussed below, within this blog. In order to best explain it, the answer will be broken down into the three phases of the standard goal shot. These phases include:

The preparation phase:

Distance

Balance and stability

Centre of gravity

Impulse and momentum

Producing power phase:

 Summation of force 

Kinetic chain

And lastly the execution phase:

Projectile angle

Projectile motion

Force

Magnus effect

In a basic throw, the preparation phase puts the body into an advantageous position for the action phase and increases the acceleration path of the object to be thrown. The action phase demonstrated a sequential action of muscles as segments are recruited into the movement pattern at the correct time. The recovery phase involved the controlled deceleration of the movement by eccentric contraction of the appropriate muscles (Bartlett, 2007).

THE ANSWER…

PREPARATION PHASE:

Distance -

In order for a player to make an accurate netball shot, they must position themselves the correct distance from the ring. The distance from which the player shoots from can either mean a hit or miss in terms of shooting and scoring. Research suggests that the further the distance the player is from the ring the less likely they are to obtain a successful shot. As it requires greater flexion of the knees and shooting elbow to create more force while also increasing release height and greater velocity (Steele, 1993). The study which Elliot and Smith (1983) produced, indicated that shooters were able to achieve an average of 79% accuracy when shooting within 1.6 meters of the ring, where as, they were only able to achieve 64.2% when shooting 1.6-3.3 meters from the post, and only 43.5% accuracy when attempting shots further than 3.3 meters from the ring.

Figure 2. (ANZ Championship, 2013)
 Showing appropriate distance from hoop to perform a successful shot.

Balance and Stability (base of support) –

Another crucial element to the preparation phase of setting up a successful netball goal shot, is for the player to take the correct stance, relying strongly on their balance and stability as well as their base of support. Balance is achieved when the body’s centre of mass lies within the base of support, either by moving the legs in one direction or by reducing the distance between the hands (Blazevich, 2010). Steele (1993) suggests that shooters should place the foot corresponding to the shooting side of the body either slightly foreword or aligned with both feet parallel, to point directly at the goal ring, spaced approximately shoulder width apart or less. By having the players position their feet in this way, it was able to provide them with a stable base of support as well as limiting their trunk rotation during the shot. It is important for skilled players to maintain a fairly upright trunk position, with their head also upright and centered in the midline of the body. Some players tend to lean backwards slightly (15 degrees from vertical) to help a balance-shooting stance (Steele, 1993).  Any excessive trunk movement during moment of ball release could potentially interfere with body balance and concentration and therefore, minimize shooting accuracy.

Figure 3. (Catherine Co, Netball Australia, 2015)
Catherine Cox demonstrating correct trunk, head and arm positioning to maintain balance and stability in order to generate a successful shot.

Center of Gravity –

Center of gravity is described by Blazevich (2010) as, the point around which all the particles of the body are evenly distributed, the point at which we would place a single weight vector, is therefore, the body’s center of gravity. The human body is made up a large number of particles; the weight of a body is a function of the mass of each particle and their acceleration due to gravity. The center of gravity in an imaginary point at which the weight of an object can be considered to act (Bartlett, 2007). Due to the nature of the netball game, players are often involved in specific movements which alter their centre of gravity, the player will therefore need to maintain stability in order to no effect their sequence of the skill, or loose possession of the ball.

Figure 4. (Applying Biomechanics to Sport, 2010)
Demonstrating how when our body movement changes, so does our centre of gravity, as there are many movement variations within netball.

Impulse and momentum –

Impulse and momentum is required with the netball shot in order to generate power behind the ball, to propel it towards and into the hoop. Newton’s Second Law states that, 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). When a ball is thrown, for example in netball, the acceleration of the ball will be proportional to the force applied to the ball by the throwers arms and inversely proportional to the mass of the ball (Bartlett, 2007). The player must therefore take into consideration the following elements in order to make a successful shot, line of action, direction of the ball, their point of application and magnitude (demonstrated in Figure 5. below).

Figure 5. (Old.netball.asn.au, 2012)
Demonstrating the four main aspects involved in generating force; magnitude both both the amount or how much is applied to the object, the direction of the acting force and specific point of application for the acting force.

PRODUCING POWER PHASE:

Summation of Force –

Blazevich (2010) describes summation of force in the following way, in order to achieve maximum force, or little force it is necessary to combine or add up the forces applied by different body parts. Summation of internal forces is most important in activities requiring speed or force, such like netball; it involves the recruitment of body segments into the movement at the correct time (Bartlett, 2007). The large muscle groups within the body typically initiate these movements, which therefore, produces force as a means to overcome inertia. In order to maximise the velocity of the ball, it is helpful to maximise the number of muscles engage, and ordered in the correct sequence. Notice in the image below (in Figure 6.) Kimberley utilises her whole body in order to generate power behind the ball to take a shot.

Figure 6. (Kimberleyjs.blogspot.com.au, 2013)
Showing the correct movement sequence to produce a summation of force within the body, beginning with raising the ball, bringing it behind the head whilst bending at the knees and finally the release of the ball, extending the body.

Kinetic Chain –

Human motion involves the complex co-ordination of individual movements about several joints at the same time. We affectively have a moving chain of body parts: the kinetic (moving) chain, subsequently there are two main categories of kinetic chain patterns: push-like and throw-like (Blazevich, 2010). Within the kinetic chain, some movement analysts distinguish between throw-like movements for distance, in which segmental rotations occur sequentially, and push-like movements for accuracy, in which segmental rotations occur simultaneously (Bartlett, 2007). Within the netball goal shot, a throw-like movement is essentially used, as the movement from each body part occurs sequentially starting proximal to the body, finishing distal, and allowing for force summation (Blazevich, 2010).

Figure 7. (Applying Biomechanics to Sport, 2010)
Graph demonstrating how the kinetic chain works within the body to create a sequential movement patter, beginning with the trunk and generating velocity over time to finally execute with the hand.

EXECUTION PHASE:

Projectile Angle –

The projectile angle is defined as the angle between the projectiles line of travel (its velocity vector) and the horizontal at the instant of release or takeoff, the value of the projection angle depends on the purpose of the activity (Bartlett, 2007). If an object is projected vertically, it will land back around its starting point, after gravity has pulled it back down, thus affecting its projectile range. In order for an object to travel both vertically and horizontally it must be projected between 0 and 90 degrees. At a projection angle of 45 degrees, the object will have an equal magnitude of vertical and horizontal velocity and its range will be maximized, (Blazevich, 2010).  Steele (1993) suggests that, a high release of the ball, within netball, was identified as helpful, contributing to accuracy by shortening the pathway of the ball travelled to reach the goal ring while still evading interception by the defending player. Release height in shooting could be improved by increasing extension at the knees and at the elbow of the shooting arm and increasing the height the shooter pushes off the ground at ball release (Elliot and Smith, 1983).

Figure 8. (Mount Albert Grammar School, 2012)
Demonstrating the projectile angle, by referring to the angle of release and the height of release in order to make a successful shot.

Projectile Motion –

Blazevich (2010) describes projectile motion as the motion of an object projected at an angle into the air, with gravity. In accuracy-dominated skills, such as set shots in netball, the release of the object needs to achieve accuracy within the distance constraints of the skill (Bartlett, 2010). Within Elliot and Smith’s (2010) study they discovered that the average angle of release in netball shooting equaled 59.8 degrees from horizontal, and the average angle of entry into the ring of the same successful shots was 43.1 degrees. Trajectory is influenced by the projection speed, the projection angle and the relative height of projection, that is, the vertical distance between the landing and release points (Blazevich, 2010). It is therefore, crucial for netball shooters to obtain an accurate projectile motion in order successfully obtain a goal shot.

Figure 9. (Quintic 4 Sports Education, 2010)
Showing how the angle of release effects the projectile motion to which the ball will travel once released.

Force –

Within the netball goal shot, force is required in order to generate power to propel the ball towards and into the hoop; force for this shot can be generated with the use of knees and arms. Forces can be defined as a push or pull motion (McGinnis, 1954). 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 from a state of rest. This therefore directly links to 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, 2010). In their study, Elliot and Smith (1983) stated how much the shooters bent their knees during the sinking action of the shot varied considerably (average = 112.6 degrees as measured between the thigh and calf). Although optimal angle of knee flexion was considered to be based on individual preference, the authors claimed adequate flexing or sinking at the knees was necessary to ensure sufficient force could be generated during the subsequent extension phase of the ball release action to propel the ball to the goal ring.

Figure 10. (BBC Sport Academy, 2011)
Image demonstrating how the human body can move in order to generate force (power) from within the body, by bending at the knees and elbows.

Flexion –

Flexion can be best described as, a movement away from the midline of the body, generating a ‘bending movement’ (Bartlett, 2007). As a means to improve shooting accuracy, a player should extend their shooting hand only as far as they feel it to be comfortable in order to stabilize the ball to prepare to shoot. Within Elliot and Smith’s (1983) research they found that, the optimal relative angle at the elbow during flexion was in the region of 90 to 104 degrees. Forceful hyperextension of the head was likely to create excessive strain and tension in the flexor muscle of the hand resulting in an increased likelihood of an uncontrolled and inaccurate shot (Elliot and Smith, 1983).

Figure 11. (Catherine Cox, Netball Australia, 2015)
Catherine Cox showing how to create flexion (bending movement) to improve shooting accuracy, she has only extended her arms as far as they feel comfortable in order to allow her to shoot.

Magnus Effect (back spin) –

H. G. Magnus attributed, in 1852 that 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 a 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). Elliot and Smith (1983) found all skilled players imparted backspin of 1 to 1.5 revolutions from release to goal entry. Additionally, backspin improved accuracy by assisting to maintain flight direction and it also reduces ball speed on impact with the ring, which, in turn, provides better opportunity for the ball to rebound off the ring and into the net (Elliot and Smith, 1983).

Figure 12. (Applying Biomechanics to Sport, 2010)
Demonstration of how the Magnus Effect is generated,  through decreased velocity, from the collision of air onto the ball, therefore creating increased velocity on the other side of the ball.

HOW CAN WE APPLY THIS INFORMATION…

Shooting and throwing objects occurs in a variety of modern day sports, where accuracy and success, plays a vital role of the victory of the game. The biomechanical principles explored within this blog can all be utilized to improve performance within a variety of other sports. For example within the sport cricket, it is of high importance to bowl the ball with the correct angle of release, as well as height of release and enough force to get the batter out. 
Through studying the biomechanical structures behind a set skill sequence, it allows educators to both quantitatively and qualitatively analyse human movement within sport. This information can then be utilized within a school setting when teaching the basics of a skill sequence; netball goal shot for example, becomes relevant. Information presented from biomechanical analyses of netball skills should provide coaches/teachers with the necessary theoretical background to teach the basics to junior players as well as to refine existing techniques of experienced players so they may achieve optimal technical performance of game skills while minimizing the potential for injury (Steele, 1993).

REFERENCES:

Applying Biomechanics to Sport. (2010). Retrieved 15 June 2015, from

http://iahf.ac.in/admin/pdf/15-11-2014-1416043807.pdf

Bartlett, R. (2007). Introduction to Sports Biomechanics – Analysing Human Movement Patterns. Routledge, New York. 2, 1-76)

Blazevich, A. (2010). Sport Biomechanics. London: A &CB.

Elliot, B. & Smith, J. (1983). The relationship of selected biomechanics and anthropometric measures to accuracy in netball shooting. Journal of Human Movement Studies, 9, 160-193.

Knudson, D. (2007) Fundamentals of Biomechanics. Springer Science+Business Media. 2, 1-10.

Steele, J. (1993). Biomechanical factors affecting performance in netball. Department of Biomedical Science. 3, 1-22.