Introduction

Netball is the most popular sport in Australia played by women with an estimated amount of one million players playing nationwide (Netball Australia, 2015). Netball is a very fast paced, skillful game that not only requires players to have speed, agility and endurance but also relies greatly on teamwork. Netball is a team sport that requires seven players from each team on the court at a time, with each only allowed in specified areas during play. The positions can be separated into two groups: the attackers and the defenders. The goalkeeper, goal defence and wing defence make up the defenders. While the wing attack, goal attack and goal shooter make up the attackers. The centre is included in both groups. Netball goal shooting is a major component within a netball game and as stated by Steele (1990) ‘shooters shoot goals and goals win games’. The ability of a goal shooter to successfully score goals is a major aspect within a game, therefore goal shooters must be able to understand the biomechanical principles of goal shooting and be able to get into a preferred shooting position as quickly as possible.

Image 1: Netball court and player positions

What is sports biomechanics?

Blazevich defines biomechanics as the “field of science devoted to understanding mechanical principles in relation to biological organisms” (2010). In order to achieve optimal technique in any skill, we must understand what factors influence the technique and what is considered optimal. Analysing a skill from a biomechanical perspective allows for optimising performance techniques.

This blog will demonstrate the specific biomechanical factors that are required for optimal execution of the netball goal shot. 

The Answer

What are the biomechanics of the netball shot?

The biomechanics of a successful goal shoot are listed below and each of these can have a major impact on the success of scoring a goal in a netball game.

There are three major phases of movement in regards to the netball shot, which are;

Preparation Phase

Release Phase

Follow through Phase

Each of these phases have biomechanical principles as well as skill cues which relate directly to the phase and need to be understood in order to be executed successfully.

Video 1. Phases of a goal shot in motion.

Video 1 shows the stages of the netball goal shot and how they link into one another. It will demonstrates the optimal performance that is going to be detailed below.

Preparation Phase – Balance and Stability

What is included in the preparation phase of the netball goal shot?

The preparation phase consists of the movements that help prepare an athlete for the performance of a skill (Pyke, 2010). To determine whether or not to shoot is a decision that every goal shooter or goal attack has to make when in the goal ring in a matter of seconds. The three key factors that influence this decision are: balance, distance from the goal ring and the position and availability of the other shooter (Woodlands, 2006). 

Balance

A netball player must be able to find their centre of mass in order to achieve balance when preparing for goal, which is done by identifying the point at which the body is evenly distributed in all directions (Blazevich, 2010). Balance (equilibrium) is an essential component in preparing to successfully execute this skill. Balance can be effected by Newton’s First Law, “An object will remain at rest or continue to more with constant velocity as long as the net force equals zero” (Blazevich, 2010, p.44). This means that when the forces acting upon the body equal zero, a state of equilibrium is achieved (Pollock, Durward, Rowe, & Paul, 2000). Being balanced allows for the goal shooter to prepare to take a shot. The quicker balance is achieved the more time there is for decision making, skill execution and processing other factors influencing the goal.

Figure 1: Centre of Gravity changes in different positions.

Distance

The distance from the goal post can have a great impact on the overall accuracy of the netball shot as the further away from the ring the shooter is, the less likely it is that a goal will be scored. Steele (1993) states that the distance from the goal post when shooting highly influences the accuracy of the overall shot while Woodlands (2006) states that ‘experienced shooters know their range and how far out they can shoot confidently’. When further from the goal ring greater flexion of the elbows and knees is required in order to generate more force.

Position

After receiving a pass in the goal circle the first foot to touch the ground (the grounded foot) is not allowed to lift off of the ground. A pivot is required to face the goal ring, resulting with feet being in line with the goal ring. It is important to ground the second leg at shoulder width apart to form a balanced base of support, which will provide stability (Blazevich, 2010). In an upright steady position the body’s centre of gravity will be in line with the base of support (Figure 1), which results in being balanced and not swaying involuntarily. If the centre of gravity is displaced outside of the base of support the body will become unsteady and begin to fall (Pollock, Durward, Rowe, & Paul, 2000).

Skill Cues

"Land in a position that will assist with gaining balance quickly."

“Stand with feet shoulder width apart with relaxed knees.”

“Keep feet facing towards the goal post.”

"Limit trunk movement to assist balance and stability."

“Raise ball above head using preferred hand while supporting with the other hand.”

How can the preparation phase help the accuracy of the netball goal shot?

The preparation phase helps the shooter maintain balance and stability when performing the netball goal shot and allowing for successful completion of the following phases, which can then lead to a goal being scored.

Release Phase – Power production

The release phase of a netball shot requires force, which is gained by using a push like movement by extending the knees and elbows in an upright position towards the goal ring. The release phase also requires the shooter to flick both wrists as the ball leaves the fingers in an upwards direction through a backwards spin which helps the trajectory of the ball.

Force
 

Blazevich (2010) defines force as being 'the product of mass and acceleration; induces a change in the mobile state of an object". Force helps to set up and determines whether or not a ball will make the distance when shooting for goal. Within netball the force of the shot can be described as a push-like movement where all joints are simultaneously extended. This movement generates force that is transferred through the body to the ball. 

Projectile motion

The projectile motion refers to the motion of an object that is projected into the air at an angle. The projectile motion within the sequence of the netball shot plays a vital role in completing the shot successfully (Figure 2). When a netball goal shooter is attempting a shot at goal, they need to release the ball at an angle that is big enough in order to obtain sufficient vertical height to reach the goal ring.

                                 Figure 2. Angle of release at 60 degrees to ensure correct vertical height and range are reached. 

Newton’s Laws

Newton's Laws can be incorporated into understanding the netball shot by allowing netball players to get a better understanding of the science behind the successful shooting technique of scoring a goal.

Newtons First Law: Inertia

‘An object will remain at rest or continue to move with constant velocity as long as the net force equals zero’ (Blazevich, 2010, p.44).

This means that to change the state of motion of an object, a force must be applied. Inertia means that an object will continue in its current state of motion. The mass of an object determines how easily the state of inertia can be altered. Inertia is relational to the mass of an object: larger objects have a greater mass and therefore greater inertia. Buses for example have a large mass and will require a greater force to change the state of motion, to increase or decrease velocity or to change direction.

The distance from the ring when preparing to shoot will determine the force that is needed to be applied to the ball (to change the state of inertia) in order to increase its velocity and project the ball towards the ring.

Newtons Second Law: Acceleration

‘The acceleration of an object is proportional to the net force acting on it and inversely proportional to the mass of the object: F = ma’ (Blazevich, 2010, p.45).

The acceleration of an object is determined by its weight and the force applied.

Force = Mass x Acceleration

If an object is lighter it will accelerate faster under a given force. This law is demonstrated when the ball is released from the hands, it accelerates, and moves towards the target. The amount of force applied on the small object needs to be appropriate as to not over shoot the target.

Newtons Third Law: Action/Reaction

‘For every action, there is an equal and opposite reaction’ (Blazevich, 2010, p. 45).

When the ball is released there is a force applied to the ball in order to project it through the air and change its state of motion. When considering energy it is important to remember "energy can neither be created nor be destroyed" (Dincer, 2002). Whether the goal is successful or not depends on how this force is transferred. If the goal is successful the ball will hit the ground and the opposite reaction is the force that causes the ball to bounce upwards. If however the goal is unsuccessful and optimal technique has not been implemented then the equal and opposite reaction occurs when the ball rebounds off the ring and travels in another direction. In either instance, the force from the shot is not lost but transferred.

Kinetic Chain

The kinetic chain is the movement of body parts. There are two types of kinetic chains, push-like movement patterns and throw-like movement patterns. The two categories differ in the order that joints move. Blazevich defines the movements as:

The throw-like movement involves the progressive extension of joints, following on from each other. This is important in:

• Increased velocity

The push-like movement involves the synchronization of different joints at the same time. When executed successfully the movement will result in:

• Force Generation

• Accuracy (2010)

A throw like movement builds upon each movementd extension and builds momentum which generates higher velocity (Blazecich, 2010). A netball goal shot, unlike a football kick down the field, does not require a large range to be achieved or a high velocity to be reached but rather an accurate action. It would therefore be less appropriate to implement a throw like motion and compromise the accuracy of the push like movement. The push like movement is commonly used to shoot for goal in netball. The flexion of the knees and elbows in the beginning of the chain movement, and the extension of the elbow and knees is the end of the chain when the ball is projected towards the target (Figure 3). When the chain is smoothly executed the accuracy of the netball goal shot can be increased.

Figure 3. Push-like movement showing simultaneous flexion and extension of the knees and elbows.

How can the Release phase help the accuracy of the netball goal shot?

The release phase of the netball shot is important as the ball follows the direction in which it was released by the shooter. The release of the ball from a higher height will shorten the path in which the ball has to travel and therefore reduces the chance of the ball being intercepted (Blazevich, 2010).

Skill Cues

“Bend knees and elbows to generate power.”

"Push through using feet, knees, elbows."

“Simultaneously bring knees and arms up towards the goal.”

Follow Through Phase - Backspin

What is included in the follow through phase of the netball goal shot?

The final phase of the netball goal shot is the follow through. In this phase the shooter must have completed the previous phases with a degree of accuracy in order to allow a successful final phase. The final phase requires the release of the ball while still maintaining the balance and stability from the previous phases. Once the ball has been released the shooter must prepare for the rebound and prepare to shoot again following the sequence beginning from phase one.

Momentum 

The goal shooter generates momentum through the kinetic chain movements. Force that is generated through the muscles and joints passes through the finger tips and generates momentum of the ball. The momentum generated by the shooter then helps prepare them for the follow through of the ball, by moving forwards.

Momentum = Mass x Velocity

The Magnus effect – Backspin

The Magnus effect is the force exerted on a spinning object moving through air or other fluids in a direction at an angle to the axis of spin (Blazevich, 2010). Goal shooters apply backspin to the ball when shooting to ensure the ball drops into the ring. This backspin on the ball is caused by The Magnus Effect. When the ball is released from the hand with a flick of the wrist, backspin is created. When the ball spins in the air, rotating in the opposite direction to the travel of the ball, air travels around the ball on both sides (Figure 4). The friction between the ball and the air causes the air to cling to the ball which forms a layer that is referred to as the boundary layer.

Figure 4. The Magnus Effect (Blazevich, p.188, 2010).

On one side of the boundary layer, the air collides with the normal passing air- this air decelerates - while the air on the other side moves freely with the surrounding passing air - this does not impact the air velocity. 

Therefore:

Higher air velocity = lower relative pressure.

Slower air velocity = higher relative pressure

The pressure differential creates a Magnus force which causes the ball to move in the direction of the difference, high to low.

Ball trajectory 

Blazevich defines projectile motion as “the motion of an object projected at an angle into the air (p. 25, 2010).” Three factors influence the trajectory: the projection velocity, distance from the target and release angle. These three factors will affect how high and how far the released object will go. Netball goal shooting does not require the ball to go far, unlike football for example, but requires higher accuracy. As there is a target that the goal shooter is aiming for (to get the ball into the ring) the angle of release needs to be within a certain range or the ball will miss the target. For successful netball shooting the vertical height should be higher which will mean the range is lower. Figure 5 from Blazevich (2010) demonstrates the impact that desired angle of release and range have on one another. Studies have shown that the optimal release angle for netball goal shooting is approximately 60 degrees from the horizontal, although certain circumstances can slightly vary this release angle such as distance from the ring and defender height (Elliot and Smith, 1983 as cited in Fairley, 2014). When relatively close to the ring, the angle of release will be greater which will cause greater vertical height and lower distance (range) and the opposite will be required when at a greater distance from the ring. To improve the height that the ball reaches, the extension of the knees and elbows should be increased. The higher height of the ball will mean that the ball will, when acted upon by gravity (an environmental factor), fall downwards through the goal ring net, reducing the chances of bouncing off of the ring. 

Figure 5. Projection angles for netball goal shooting (Blazevich, p. 26, 2010).

Skill Cues

“Follow through with a flick of the wrist.”

"Extend shooting arm to decrease the distance between you and the goal post."

“Prepare for rebound.”

How else can we use this information?

Within the phases 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. Furthermore, constraints such as defenders, weather and personal ability (Davids, Button, Bennett, 2008) can all have an impact on a goal shooter's chance of performing an accurate goal shot. Practice with the use of constraints can benefit and improve the goal shooter's ability to over come issues they may face during a game situation.

Once the biomechanic principles are understood, the knowledge can then be transferred to analysing other sports. We discussed the ball release in the netball goal shot and described why height was more important than range. Other sports have different outcomes that require different actions to be taken. For example, the optimal ball release in the cricket bowling action would be different to the optimal ball release point in the netball goal shot. In cricket the target is lower to the ground and further away from release point, which means that the ball is going to be released lower and at a higher velocity to achieve the distance.

Other sports can be examined by using the same principles used above but in different ways. An example would be Newton's third law. The equal and opposite reaction of the ball varies between sports. In netball it is seen after the ball has been released as it rebounds off the ring. In cricket, however, it occurs at the beginning of the follow-through phase: the momentum of the body after releasing the ball.

The information that has been presented regarding the biomechanics of a successful goal shot within netball can be useful for teachers, coaches and players. The same biomechanical principles applied to determine the optimal netball goal shot can also be used to examine other sports optimal technique such as the basketball shot. Understanding the phases of the netball shot and the biomechanical principles used such as Kinetic chain, Ball trajectory, force and velocity to name a few can allow for understanding of how to create the optimal technique for any sport. 

   

Understanding the concepts of biomechanics allows for the modification of techniques to be perfected.

References

Blazevich, A. (2010). 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

Dincer, I. (2002). The role of exergy in energy policy making. Energy policy, 30(2), 137-149.

Elliott, B., & Smith, J. (1983). Netball shooting: a statistical analysis. Sports Coach, 7(1), 29-37 as cited in Fairley, A. (2014). What Biomechanical Factors can improve a Netball Goal Shooter’s Accuracy?. Biomechanics and Goal Shooting Accuracy. Retrieved from http://biomechanicsandgoalshootingaccuracy.blogspot.com.au/

Netball Australia,. (2015). What is Netball? - Netball Australia. Retrieved 12 June 2015, from http://netball.com.au/our-game/what-is-netball/

Pyke, F. (2012). Methods of movement analysis. Human Kintetics. Retrieved from,http://www.humankinetics.com/excerpts/excerpts/methods-of-movement-analysis

Pollock, A. S., Durward, B. R., Rowe, P. J., & Paul, J. P. (2000). What is balance? Clinical rehabilitation, 14(4), 402-406.

Steele, J. (1993). Biomechanical factors affecting performance in netball. Department of Biomedical Science. 3, 1-18.

Steele, J. R. (1990). Biomechanical factors affecting performance in netball. Sports Medicine, 10(2), 88-102.

Woodlands, J. (2006). The netball handbook. Human Kinetics.