Monday, 29 April 2013

Biomechanics of Netball shot.

Biomechanics is a study of forces and their effects on living systems (McGinnis, 1954). The study looks at the body and both the internal and external forces that act on it. By understanding the concepts of biomechanics, it can be clear to program out body to move with precision. Furthermore this study enables us to research the technical error, decrease injury and comprehend the significance of equipment design. 

This study will be directed towards looking at the biomechanics of a netball shot at goal. 

The question:
To understand this question we need to understand what is involved in producing this skill.

-          Shooting action
-          Balance and stability
-          Ball release
-          Ball  Trajectory  
-          Distance from the goal post
-          Backspin
-          Magnus effect
-          Netball shoot sequence

Shooting action
Forces can define as a push or pull (McGinnis, 1954) or anything that causes or has potential to cause movement. Forces can be described as internal (act within the object or system whose motion is being investigated) or external (act on an object as a result of its interaction with the environment). For Example muscles and bones are regard as inside the system therefore, are internal forces, any forces applied outside the body e.g. gravity, contact with the ground or another person and friction are all external forces.  The motion we are curious about is the force directed upon the ball as it travels to the goal ring.

The tendency for an object to remain in its present state is called inertia, often referred to as Newtons Law of Inertia. This law states:

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).   

This means that if we want to change the motion of an object, we need to apply a force.

Figure 1.1: Forces of have four properties

All forces have four common properties:

-          Magnitude (the amount, and how much applied)

-          Direction( the angle at which the force is applied)

-          A point of application (the specific point at which the force is applied)

-          A line of action (represented by a straight line through the point of application in the direction that the force is acting).

(Hede, C., Russell, K., & Weatherby, R. 2011).

Figure 1.2:  the sequential summation of force from body parts is essential to maximise force production.

As a goal shooter in netball, we propel the ball through legs, trunk, shoulders, arms, and wrist.  Many shooters bent 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). To gain a more accurate shot for goal, many shooters tend to flex their forearm at the elbow. The optimal angle for elbow flexed stated in Biomechanics factors affecting performance in netball (1993) was 90 to 104 degrees.
How does this relate? Shooter should extend the shooting hand only as far as necessary to stabilise the ball in preparation to shoot. Try to evade unnecessary hyperextension of the hand at the wrist.  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).

Additionally there is no single or optimal target for skilled shooters to focus on when preparing to shoot.   Where a shooter focuses upon when preparing to shoot is one of personal preference (Steele, 1993).  

Figure 1.3: Shows the simultaneous motion of flexion of knees and elbow.
Balance and stability
All humans and objects have a centre of gravity.  Blazevich (2010) states “the point around which all the particles of the body are evenly distributed, and therefore the point at which we could place a single weight vector is the body’s centre of gravity”.  Centre of gravity cannot be easy to find the exact centre of gravity on a human, especially in sport.

Excessive trunk movement during the shooting action could hinder with stability and body balance. Therefore, there is minimal movement of the truck and arm movement (Steele, 1993). Having a solid structure for balance and stability will allow for optimal performance to execute an accurate shot at goal. 
Figure 1.4:  A body’s centre of gravity can shift, depending on the body’s movement and position.

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).  

Figure 1.5: A projectile flight is affected but its angle of release, height and speed of release. The optimal angle of release for a shot at goal is approximately 60 degrees.
Ball Trajectory
Projectile motion refers to the motion of an object (Blazevich, 2010).  This could be a shot, ball or human body projected at an angle into the air. Such factors that affect projectile are gravity and air resistance.  Trajectory of a ball is influenced by projection speed, the projection angle and the height. Steele (1993) implies the average angle of entry of a ball through the goal ring is 43.1 degrees. This angle of the shot was proven to be optimal due for the tolerance for error.  When a shooter is close to the goal post the projectile motion is 90 degrees vertical and zero degrees horizontal. The speed of the projection object will be determined by height it reaches before gravity accelerates in back down to earth (Blazevich, 2010). 
Back Spin
A study conducted by Elliott and Smith (1983) found all elite players used backspin of 1 to 1.5 revolutions from the release to entry of goal (Steele, 1983). Backspin is found to improve accuracy by supporting to maintain flight direction and decrease ball speed on impact with the goal ring. Therefore offers a better chance for the ball to rebound off the ring and through for a scored goal.  

Most elite shooters are quite tall in structure and less mesomorphic (muscular). These athletes have stronger knees and elbows as these muscles are consistently being used. Catherine Cox (pictured) is known as one of the most recognisable netballers in the country. She has represented Australia in both Commonwealth Games and National Test Caps. As a goalie Cath is aware of the principals involved in a netball shot in order to produce an accurate shot at goal.

Distance from the post
Distance is also another factor that will impact on a netball shoot. The results showed as the distance increased from the goal post accuracy decreased on the netball shot (Elliott and Smith (1983). The optimum distance for goal scoring was between 3 and 5 feet (0.9m to 1.5m) from the post.  When the shooting range (or distance) has increased, shooters will require a change in the mechanics of the shooting action.
 For example shooting 4-5 metres out from the goal post will require:
-          an increase in force produce on the object (netball)
-          Projectile angle increased, height will be increased.
-          Increased speed of motion on the ball
-          Deeper flexion of knees and elbows to produce a greater  force
All the above factors will influence the accuracy of the netball shot.

The Magnus effect
Blazevich (2010) describes the Magnus effect as changing the trajectory of an object towards the direction of spin, therefore resulting in a Magnus force (lift force acting on a spinning object). It is explained that a spinning ball ‘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 1.6: 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). On the other side the air moves past unobstructed, therefore one side the air is less and than the other side (Blazevich, 2010). In netball and basketball places backspin of the ball will allow it of a chance of bouncing on the ring and dropping through the net. 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 into the goal ring.
Figure 1.6: (Knusdon, 2007).
Netball shot in sequence:
In the first 4 frames we can see:
-          Centre of gravity is centre to mass (person is balanced and stable)
-          Flexion of the elbow as ball it placed behind head
-          Flexion of the knees to produce a force on the ball
-           Simultaneous flexion of both knees and elbow in same motion

In the last 2 frames we can see:
-          The angle of release
-          Extension of the knees and elbows to produce force on the ball
-          Right arm is fully extended
-          Backspin is placed on the ball by flicking of the hand and fingers
-          The flight of the ball is vertical and then drops down due to gravity

Through the analyses of biomechanics any sport can be examined. Information of such principles will allow coaches and teachers to instruct players and students to execute the skill to their optimum (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). The above information will allow students and players to understand the biomechanics of a netball shot. This data can be used in physical education lesson or as a coaching tool. There will be other sports where this information will be helpful, e.g. basketball. An understanding of biomechanics will enable students to think critical about sports and also improve their performance.
Reference list:
-          Blazevich, A. (2010). Sports biomechanics the basics: Optimising human performance. Bloomsbury: Black Publishing.
-          Knusdon, D. ( 2007). Fundamentals of biomechanics: Department of Kinesiology. California Springer Publishing. 2, 4-334.
-          McGinnis, P. M. (1954). Biomechanics of sport and exercise (2nd ed.) Champaign, IL: Human Kinetics.
-          Steele, J. ( 1993). Biomechanical factors affecting performance in netball. Department of Biomedical Science. 3, 1-18.