What biomechanical principals underpin the 'optimal' technique of the netball static single hand goal shot?

Figure 1: The goal shot at the elite level

The goal shot is one of the most important skills in the game of netball. It is the only way a team is able to score and win a game, so it is important that the goal shot is learnt and practiced using the correct technique. There are many factors that can influence a successful goal shot. This blog will explore and discuss the biomechanical principals that underpin the 'optimal' technique and how they can be used for netball goal shooting.

This blog will break the skill of netball goal shooting down into 3 different movement phases:

• Preparation phase
• Force production phase
• Shooting phase

Refer to figure 2.

Figure 2: The 3 movement phases of the netball shot

Biomechanical Principals related to each movement phase

Preparation phase:

• Base of support
• Balance
• Stability
• Center of gravity

Force production phase:

• Summation of forces
• Newton's Third Law of Motion

Release phase:

• Height of release
• Angle of release
• Projectile motion (trajectory)
• Magnus effect (backspin on the ball)

Lets explore the...

Preparation phase:

Shot preparation is the basis of a great netball shot. Like anything, without good preparation the end result is never 'optimal'. A study by Steele (1993), of 12 highly skilled shooters showed that 58% of the time, from when the ball is caught to when it is released is spent in the shot preparation phase, and the left over 42%of the time is divided over the last 2 phases. 

The preparation phase should be used to steady the ball and establish balance and concentration.

To obtain these intended outcomes there are a number of biomechanical principals that can be implemented. 

To begin with, a steady base should be established. both feet should be aligned, a shoulder width apart and placed parallel to the target (goal ring). This stance is proven to aid accuracy and to stop trunk rotation during the shooting action. The shooter should keep a straight trunk position, leaning 15 degrees backwards (Steele, 1993)  of the body's center of gravity (Otago, 1983). "Center of gravity is the point about which the sum of all these torques is zero" (blazevich, 2012 pg.65). Refer to figure 3.

Figure 3: The body"s enter of gravity can change depending on body position

The head should be alligned in the center of the body. By synchronizing all of these factors head and trunk movement will be minimal resulting in greater Static balance (United States Tennis Association, 2013) , stability, concentration and a steady ball, resulting in a more accurate shot.

Natalie Medhurst is known as one of the most technically correct and accurate goal shooters in the world. She shoots at an average of 91% and displays all of the biomechanical principals mentioned in the preparation phase. Refer to video 1 for her technique.

Video 1: Natalie Medhurst goal shooting

Force production phase:

The force production phase is important as this is where the body and ball gains momentum and force to deliver the ball into the net. without efficient and sufficient force production, the netball shot will suffer and accuracy will be affected. Netball shooters do not only have to produce force they also have to control and direct these forces.

force production in the netball goal shot is largely due to summation of forces. 'To achieve maximum force, or little force it is necessary to combine or add up the forces applied by different body parts' (Blazevich, 2007, pg. 34). These forces are generated predominately through Flexion of the elbow, knees and ankles and hyper-extension of the wrist. Refer to Figure 4 for examples of optimal flexion.

Figure 4: Optimal flexion measurements (Elliot & Smith, 1983)

The flexion of the ankles were found to be left to personal preference, as long as the shooter could generate enough force to successfully shoot the netball. The wrist again had no optimal angle of hyper-extension, it is left to the individual. It is advised that the wrist is not over hyper-extended as it puts tension on the flexor muscled and can result in decreased accuracy (Elliot & Smith, 1983)

More importantly is the flexion created at the knees and elbow. Elliot & Smith suggests that the optimal flexion at the knee during the 'sinking' action of the force production phase is 112.6 degrees, measured between the hamstring and the calf. Optimal flexion at the elbow was found to between 90 and 104 degrees, measured between the bicep and the forearm. Although the more successful shooters demonstrated greater flexion at the elbows.

To ensure optimal force summation the ankles, knees, and elbow should be extended and the wrist flexed simultaneously. This technique is implemented to increase accuracy rather than velocity (speed) (Elliot & Smith, 1983). 

This synchronization of movement also relates to Newton's Third Law of Motion: "For every action, there is an equal and opposite reaction" (Blazevich, 2012 Pg. 45). 

Figure 5: Newton's Third Law of Motion

As the ankles and knees flex, the force created travels through the trunk of the body, through the legs and feet until it hits the ground. the ground then sends and equal and opposite reaction back through the feet, legs and trunk (refer to Figure 5) which help propel the body upwards generating the force needed to shoot the netball.

It is also important to note that to ensure optimal performance a steady trunk, arm and forearm position is carried out from the preparation phase through to the force production phase.  

Shooting Phase:

The shooting phase is the most technical phase of the shooting action. If this phase is not executed properly they the likelihood of a successful shot attempt is unlikely. The 'moment of release' is possibly the most critical moment of all 3 movement phases.

At the moment of release there are a number of biomechanical principals that can be applied to obtain optimal performance, such as Height of release, angle of release, projectile motion (trajectory) and the Magnus effect (backspin).

It is important to to continue to keep balance, stability and concentration throughout the shooting phase following on from the first 2 movement phases. this is obtained through keeping the steady base set in the preparation phase, keeping a steady trunk position and an upright head position.

Height of Release

At the moment of release the shooting arm should fully extended without being locked or stiff. The ball should be released from above the head, centrally aligned to the body. refer to Figure 6.

Figure 6: Arms extending and the ball is centrally aligned 

Elliot and Smith (1983) found a liner relationship between height of release and success rate. The higher the point of release = a higher % of successful goal shots. This is because the ball has less distance to travel in the air, therefor having less air time, allowing for less influence by outside forces on the ball, such as wind and gravity. A high release point also allows the goal shooter to evade defenders. Refer to Figure 7.

Height of release can also be increased by greater extension of the Knees and ankles and keeping a straight trunk position. Similarly to the elbow, the knees and ankles should be extended as much as possible without being stiff or locked. Refer to figure 7

Figure 7: Characteristics and benefits of a high release point

Angle of release & projectile motion

Angle of release and projectile motion are linked very closely. depending on what angle and how fast the ball is released from the hand influences the path the ball will take in the air  therefor influencing the accuracy of the shot.

Elliot & Smith's (1983) study provides evidence that when a successful shot is made the angle at which the ball leaves the hand is 59.8 degrees from the horizontal (refer to figure 8), this number was an average of all successful shots made by 12 elite athletes. What this information doesn't take into consideration is that not all the athletes were the same height, so this number can only be an approximation. As a guide shooters should be aiming for an angle of release of approximately 60 degrees for optimal technique and greater success rate.

The same study also indicated that the optimal angle the ball should enter the goal ring is 43.1 degrees from the horizontal of the top of the goal ring. Refer to figure 8.

Figure 8: Optimal angle of release and entry of the ball

Optimal velocity of the ball once released from the hand generated from the summation of forces from the ankles, knees and elbow in the force production phase has divided opinions when it comes to optimal performance. As there is very little research on  netball goal shooting biomechanics, the research has been divided. Elliot & Smith (1983) suggest that better shooters shoot the ball with less velocity, whereas Otago (1983) suggests a higher success rate when the ball is shot with greater velocity. 

Due to this divide in opinion, it is up to the  athlete to find what works best for them, this will only come through practice, experience and analysis of their own technique and results. Optimal velocity can be established by ensuring the ball leaves the hand at an angle of approximately 60 degrees and enters the ring at an angle of approximately 43 degrees.


The Magnus Effect

Elliot & Smith's research indicates that when shooting a netball, for optimal accuracy and success rate there should be back spin on the ball. there are a number of reasons for this. By having backspin on the ball it aids with maintaining the flight direction of the ball (Knusdon, 2007). Backspin on the ball also reduces the speed at which the ball makes contact with the goal ring, increasing the chance of the ball rebounding into the net. finally by applying backspin on the ball, it alters the trajectory of the ball, increasing the angle at which it may enter the ring, this is what is called The Magnus Effect (refer to figure 9), which results in a larger margin for error. For optimal performance and increased accuracy 1-1.5 rotations of backspin on the ball are recommended from the time the ball leaves the hand to goal entry.

Figure 9: demonstration of The Magnus Effect (Knusdon, 2007 Pg.7)

Re-visiting the question

What biomechanical principals underpin the 'optimal' technique of the netball static single hand goal shot?


The Answer

To obtain the 'optimal' technique for the netball static single hand goal shot there are numerous amounts of biomechanical principals that can be implemented. This blog focuses on number of key principals that can be easily adapted to any netballer's shooting technique to help improve success rate. To answer the question again the shooting action will be broken down into the 3 movement phases. The biomechanical principals that underpin the optimal technique in the:

Preparation phase

• base support
• balance
• stability
• center of gravity

These principals ensure that the shooter is steady and well balanced setting them up for a successful shot at goal. this is done by placing the feet parallel to the target at a shoulder width apart and keeping a straight trunk position. It is important to get the preparation phase right as it makes up almost 60% of the shooting movement and set up the body for the next 2 movement phases. 

(Elliot & Smith, 1983)

Force production phase

• Summation of forces
• Newton's Third Law of Motion

These principles ensure that there is enough force generated to propel the netball into the ring. without sufficient force production the shot is futile. Adequate force is produced through the flexion and extension of the ankles, knees and elbow of the shooting arm, the hyper-extension and flexion of the wrist and the equal and opposite reaction force generate from the summation of forces impacting the ground.

(Elliot & Smith, 1983)

Release phase 

• Height of release
• Angle of release
• Projectile motion (trajectory)
• Magnus effect

These principals are critical to the success of the shot. Without executing this movement phase correctly it is highly unlikely the shot will be successful. Maximal height of release is obtained by fully extending the ankles, knees and elbow of the shooting arm without being stiff or locked and keeping a straight trunk position. Angle of release is optimal when the ball is released from the hand at an angle of 59.8 degrees from horizontal,  there should be sufficient velocity on the ball to allow it to enter the goal ring at an angle of 43.1 degrees. There should also be 1-1,5 rotations of backspin on the ball to help maintain its flight path, reduce the speed the ball contacts the goal ring and change the trajectory of the ball to increase the angle it enters the goal.

(Elliot & Smith, 1983).

Who else can use this information?

The skill of the netball goal shot is very similar to the basketball free throw skill. Both skills have the ability to apply the same biomechanical principals to optimize performance. There may be slight differences in specific detail such as angle of release and the angle the ball should enter the hoop due to the increase in the size of the hoop and the distance the ball is shot from. but in principal this information can be applied to both sports. 

When the skill is broken down and each individual biomechanical principal is analysed separately, they can be implemented in nearly every sport in one way or another. A couple of examples could be; The Magnus Effect and  Newtons Third Law of Motion. 

The Magnus effect is often applied to the baseball pitch. The pitcher releases the ball with side spin in hope of getting the ball to swing towards the direction of the spin. This is commonly known as the 'curve ball' (Robertson, 2009). 

Newtons Third Law of Motion can also be applied to the spike in volleyball. The more force the volleyballer strikes the ground with their feet will determine how high they will be able to jump in the air to strike the ball due to the equal and opposite reaction forces created between the feet and the ground. 

References

Blazevich, A. (2007). Sports biomechanics the basics: Optimising human performance. Bloomsbury Black Publishing.

Knudson, D. (2007). Fundamentals of biomechanics: Department of Kinesiology. California Springer Publishing. 2, 4-334.

Otago, L. (1983). A game analysis of the activity patterns of a netball player. Sports Coach. 7(1), 24-28.

Robertson, W. C. (2009). Science 101: What makes a curveball curve? Science and Children, 46(7), 59-63.

Steele, J. (1990). Biomechanical Factors Affecting Performance in Netball. Sports Medicine. 10(2), 88-102.

Steele, J. (1993). Biomechanical Factors Affecting Performance in Netball. Department of Biomedical Science. 3, 1-18.

United States Tennis Association. (2013). Sport Science. Retrieved from: http://www.usta.com/improve-your-game/sport-science/114378_technique_basic_terms_and_principles_in_biomechanics/