What Biomechanical Principles Must be Applied to Best Perform an Accurate Goal Shot in Netball?

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

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