Sunday 14 April 2013

How can a goalie improve the accuracy of her netball shot?




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, p. 3). In relation to the game 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.
Preparation of the netball shot
 





Every athlete must be able to maintain balance and stability. An athlete’s loss of stability can have an adverse effect on their ability to perform the skills of the given sport (Hede, Russell & Weatherby, 2011, p. 7). 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. As shown in Figure 1.1  you can see a low centre of gravity above the base of support improves stability.
 


Figure 1.1 shows how the body’s centre of gravity can shift depending on the body’s movement and position.  When shooting a goal in netball often the athlete is in a static position meaning when the body is at rest (Blazevich, 2007, p. 125).   It is important to note, however, that a body may be stable in one direction but not in another. For this reason, it is essential to consider the orientation of the base support to the force being applied. For example as there is not much force needed to shoot the netball the athlete will only have their feet shoulders width apart, however, a wrestler for example wanting to prevent being pushed back will brace himself by placing his feet in a wide stance and having one foot behind the other (Hede et al., 2011, p. 7).  A study by Elliot and Smith (1983, p. 14) 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 the ring ?
Another aspect to consider when shooting the netball 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, p. 4). The further away the netballer is to the ring the less chance they will have of getting it in. As the netballer is further away from the ring they need to demonstrate greater flexion of the knees and shooting elbow to create more force while also increasing release height and greater velocity (Steele, 1993, p. 5). 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 in the longer shots (Knusdon, 2007, p).


















Shooting Action
Force is anything that causes or has the potential to cause the movement, diversion or slowing of the object on which it acts. This relates 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, 2007, p. 125). All forces have four common properties, magnitude, direction, a point of application and a line of action.



   Figure 1.3  ( Knudson, 2007, p.7)

Figure 1.2 ( Knudson, 2007, p.7)





Figure 1.3 shows where these four common properties are located when shooting a basketball. Force production is not necessarily just about producing the most force possible. For the skills, such as shooting a basketball goal or netball goal, accuracy is critical for success. The player therefore must be able to control both the amount and direction of force produced.  To obtain maximum force, or little force it is necessary to combine or add up the forces applied by different body parts (Blazevich, 2007, p. 34). This concept is known as the summation of force, Figure 1.4 shows the sequential summation of force starting from the trunk of the body.  Figure 1.5 shows a netballer in the shooting position, as you can see the knees are bent slightly creating force the trunk position is straight and the arms the elbows are slightly bent increasing hand motion, greater release height and greater release velocity ( Blazevich, 2007, p. 35).
 
 Figure 1.4
 
 
 
 
 
 
 




                        Figure 1.5
 
 
 
 











Projectile motion 
From the above information we now know that balance and force are two important biomechanic principles when shooting netball.  However the projectile motion of the netball shot is also important. Projectile motion refers to the motion of an object projected at an angle into the air(Blazevich, 2007, p. 125).    The angle of projection is an important factor affecting the projectile range. If an object is projected vertically, it will land back as its starting point, after gravity has pulled 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. A study done by Elliot and Smith (1983, p. 7 ) found that the average angle of release in netball shooting equalled 59.8 degrees from the horizontal.  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 this effects the angle of realise. As you can see in figure 1.6 the defender from Victor Harbor netball club is very tall. The Netballer must project the ball with greater angle and veloicty height to aviod the netballers hand.
 

















The relative height of projection is also important when trying to improve accuracy of the netball shot.   The height of projection is the vertical distance between the projection point of an object and the point at which it ands ( Blazevich, 2007, p. 130). When shooting the netball close to the ring players need to project the ball with maximum vertical velocity  the netball will therefore  not travel horizontally over the ring (Blazevich, 2007, p. 125).   A high release of the ball contributes to accuracy as it also shortens the pathway the ball has to travel to reach the goal ring. Once a projectile has been released, its horizontal velocity remains constant for the duration of its flight. 
Follow through





Often when a projectile is thrown, techniques are used to cause the projectile to spin. The Magnus effect occurs when a spinning object is moving through air or water, this can be seen in figure 1.6. As shooting a netball is more about accuracy often netballers decrease the release speed placing more emphasis on perfecting the angle and height of release (Blazevich, 2007, p. 125).    However, a study by Elliot and Smith (1983, p. 5) found that skilled netballers implied a small amount of backspin to increase the entry angle of the ball to rebound off the ring into the net. This is because when a spinning ball bounces, it always bounces in the direction of the sin on the ball. A backspin on the ball tends to make it bounce backwards into the net.
Figure 1.6 (Knusdon, 2007, p. 7)
 
 











The Anwser
How does understanding all this allow us to determine how a goalie can improve the accuracy of her netball shot? The factors we need to consider when working out how a netballer can improve the accuracy of her netball shot can be summarised as:
  • Preparation:

In preparing to shot place the foot corresponding to the shooting side of the body either slightly forward or aligned both feet parallel to point directly at the goal ring, spaced approximately shoulder width apart or less. The knees should also be slightly bent. This foot placement facilities accuracy by providing a stable base support minimising trunk rotation. The centre of gravity is lowered by slightly bending the knees assisting the base of the support even more.      

Implications: minimise head and trunk movement while preparing to shoot to ensure stability.

To enhance the accuracy of the netball shot athletes should be encourage to manoeuvre the ball as close to the goal ring as possible before shooting. A study by Elliot and Smith ( 1983) found that preferable between 0.9m and 1.5m from the post was the best spot for improved accuracy.
  • Shooting action:
Flexing or sinking at the knees is necessary to ensure sufficient force can be generated during the subsequent extension phase of the shooting action to propel the ball to the goal ring.  As already stated athletes must be able to control both the amount and direction of force produced during the shooting motion. Therefore to improve accuracy the netballer should slightly flex the elbow, sufficient but not excessive hypertension of the hand to stabilise the ball, minimisation of trunk, arm and forearm movements during the shooting action in favour of increased hand motion, creating greater force for the release height and release velocity.

Implications: To improve shooting accuracy players should extend shooting hand only as far as necessary , avoid hypertension of the hand at the wrist and decrease movement of the trunk and forearm is recommended in the shooting motion.
 
  • Projectile motion 
To improve accuracy of the netball shot when close to the ring, the athlete needs to shot the ball at a greater angle to attain greater vertical height and less range. The relative height of projection is also important. The athlete needs to project the ball with maximum vertical velocity. A high release of the ball contributes to accuracy as it shortens the pathway the ball has to travel to reach the goal range.
 
The Magnus effect occurs when a spinning object is moving through air or water. To improve the accuracy of the netball shot the athlete should use backspin to assist the flight direction. It also reduces the ball speed impact with the goal ring which, in turn provides better opportunity for the ball to rebound off the ring and into the net. Wrist Flexibility can be modifies through using appropriate training exercises.
 
Implications: Release height in shooting could be improved by increasing extension at the knees and at the elbow of the shooting arm. Optimal shot for goal would be realised at an angle of approximately 60degrees, with a backward spin of 1 to 1.5 revolutions in relation to its direction of travel.
How else can we use this information
We see  this shooting technique in many other sports. In basketball, and other throwing games accuracy is vital to the success of the game. We can now use our understanding of the biomechanical principles such as balance, summation of forces, Magnus effect and projectile motion 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.
From analysing the netball shot we know that the athlete must project the ball with maximum vertical velocity to improve accuracy. However in cricket the ball needs to cover  a long range to reach the batter and therefore, we can encourage the athlete to try find a projectile angle that has equal magnitude of vertical and horizontal velocity which will then increase the range of the throw. As can be seen in Figure 10 an object thrown at an angle to low the object doesn’t have sufficient vertical velocity to attain significant range. An object projected vertically will land back at its starting point, after gravity has pulled it back to earth. We can use this information to help athletes understand the biomechanical principles of throwing an object and what needs to be down to improve the range or vertical height the ball covers.
The above information allows us to firstly understand the biomechanical principles of the netball shot and then use this information to understand how to improve accuracy. Understanding the initial movement is central to health and physical education not only for acquiring the skills, concepts and strategic awareness required for physical activity participation and enhanced  performance but also as a medium for learning across this curriculum area.  
References
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.

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

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