The Question, The Answer, The How.

The Question

 

Every now and then you will hear the commentators at an Australian Rules Football (AFL) match say, ‘your an AFL footballer you should be able to kick that goal’. What they are saying is that at the elite level of footy the players should be able to kick more set shot goals then they miss.

But is it so easy to kick a set shot goal accurately when you have 50,000 screaming fans trying to put you off?

The answer might not be as simple as ‘yes’ or ‘no’ but what we do know is that there are several biomechanical principles as well as numerous physiological process that occur during a set shot at goal. The following blog will aim to provide an understanding at how the set shot at goal works by applying the appropriate biomechanical principles and knowledge to the task at hand. After reading you will be lining up at full forward and kicking goals like the greats of the game....

The Answer

 

To accurately perform a drop punt set shot at goal several factors are at play. Certain factors are controlled by the performer; body position, ball drop, force on contact, angle of release and summation of forces. Other factors you have an influence on but are ultimately out of your control such as the Magnus effect.

An accurately performed football set shot at goal can be achieved once the important biomechanical principles are known and the performer can practice. Whilst I cannot guarantee you will kick more goals then points I can assure you that the more you know about the how, the better off you will be in perfecting the set shot at goal in terms of both accuracy and distance.

So how did we get to the answer? Below the important information required for you to know when taking a set shot at goal is detailed for you to read and in no time you will be kicking like the greats of the game.

Just like Jack Riewoldt who kicked the most goals in a season at the elite level, the video shows a near perfect biomechanical action…

 

 

Summation of Forces to Produce a Kick

 

 

The summation of forces also known as the Kinetic Chain is the body's ability to sequentially segment all the body parts from largest to smallest in order to produce a ‘push’ or ‘throw’ like movement pattern. In order for the ball to propel forward an amount of velocity has to be generated from the swing through of the leg to the optimal point of contact between the foot and the ball. Blazevich (2010) explains that the kinetic chain of the kick begins with the performer first drawing the leg back, before swinging forward through where the muscles around the hip accelerate the thigh segment, before the leg and foot swing through later in the kick cycle resulting in something resembling a throw-like movement pattern with high velocity (refer to figure below).

The speed (velocity) of the swing through of the leg will also determine the distance the object or football in this case travels. The higher the speed of the foot swing through the greater the distance that can be achieved due to a greater power generated through the summation of forces. This theory is reinforced by a study conducted by Ball (2008) where, "foot speed was the major contributor to kicking distance, with larger foot speeds being associated with longer distances."



Figure from Blazevich (2010) shows the phases of a kick from backswing to foot-ball contact.


There are 7 biomechanical principles that can be involved at any one time to explain how all movements are produced. Principles #2 and #3 come under the heading of ‘Maximum Effort’ and refer to the kinetic chain and how it produces force at foot-ball contact.

Principle #2: The production of maximum force requires the use of all the joints that can be used.

Principle #3: The production of maximum velocity requires the use of joints in order from the largest to the smallest.

Principle #6: Angular motion is produced by the application of force acting at some distance from an axis (or a torque) (Taylor, 2013), comes under the heading Angular Motion and is applicable when the foot makes contact with the ball after the torque has been produced by the by the leg acting away from the axis.

How Do We Kick the Ball Accurately using our body?

 

In order to kick the ball a great distance force you are required to put into practice the biomechanical principles of angular motion and maximum effort. In order to kick the ball accurately you need to introduce a new biomechanical principle known as STABILITY. Biomechanical principle #1 states that, “The lower the centre of gravity, the larger the base of support, the closer the line of gravity to the centre of the base of support, and the greater the mass, the more STABILITY increases” (Taylor, 2013). So why stability? well as in most sports and skills if you want to go straight your body has to be lined up straight and you have to be balanced because your body position has a direct correlation to where you are going.

In cricket if you want to produce an accurate throw-like motion you need to point in the direction you want to throw the ball with your non throwing arm then produce your throw which will follow the same path. So it would make sense to say that if you want to kick straight you will need to have your support leg lined up straight. An article entitled ‘The Best Foot Forward’ by Geoff Maslen (2011) printed in the Age newspaper looked at the research conducted by Dr Kevin Ball into the best kicking technique to produce the most accurate set shot at goal. Dr Ball in his research found that the supporting leg also known as, “the player’s ‘dynamic balance’ — his ability to brake or to stabilise the body as he kicked the ball” is explicitly important in determining the distance and accuracy of the drop punt kick. Anderson and Sidaway (2013) in a similar study into Kicking Biomechanics and the importance of balance determined that, “Single-leg balance was significantly correlated with kicking accuracy”.


Figure show how you can improve balance and thus dynamic balance in you stabilising support leg.

Thus the conclusion drawn is that stability is important in taking an accurate set shot at goal. If your dynamic balance provided by the supporting leg can stabilize your body then your kicking leg will come through straighter producing a more accurate kicking motion. One AFL hall of famer who was known for his straight kicking at goal was Matthew Lloyd. His kicking routine was the object of much ridicule and frustration by fans and opponents alike but it was proven to be extremely accurate as he produced a 2-1 goal to goal to point ratio which few players can boast who have kicked over 500 goals (he kicked 900 in his career).


Matthew Lloyd of the Essendon Bombers football club in the AFL Australia’s professional sports league.

 

So Biomechanically now I am sound, How do I know what the ball will do in flight?

 

This part is a little tricky so stick with me here. First I will explain Newton’s first law & the Magnus Effect, then I will explain how adding lift will get the drop punt to go accurately in flight.

Newton’s First Law states: An object will remain at rest or continue to move with constant velocity (speed + direction) as long as the net force equals zero. This law is also known as ‘the Law of Inertia’ because inertia is the term referred to if an object remains in a constant state (Blazevich, 2010, p.44). What also is associated with Inertia is the mass of the object and if the mass of the object is larger then it takes more inertia to move it off its projected path.
Newtons First Law spawned further research by one H.G Magnus into a phenomenon known as the Magnus Effect. The Magnus Effect states that if sideways pressure is applied to an object moving straight, then the object will deviate in that direction. How this works for example is, “that a spinning baseball ‘grabs’ the air that flows past it because of the friction between the air and the ball, so these air particles start to then spin in the direction of the spin (Blazevich, 2010, p.188).

So we now know about Newton’s 1st Law of motion & the Magnus Effect and how they will influence a spinning round ball. Both these principles apply to a drop punt set shot when coupled with the notion of ‘Lift’. (Diagram below shows the principle of 'Lift')



The principle of Lift is important to an AFL set shot at goal because lift will generate distance and accuracy. Bernoulli’s Principle states that if there is a greater pressure below the object then above the object (accounting for gravity already that forces an object with mass in a downward direction) then the pressure differential will cause the object to produce a lift force (Brown, 2000). So if an object is thrown or kicked directly upwards it will travel in an upwards direction due to the force applied below being greater then above but alternatively that object will eventually have the forces of Gravity overcome the force from the hand or foot and thus the object will return in a down direction.

Finally how these 3 principles work together to apply to a football drop punt!! First look at the diagram below of the Magnus Effect at work then I will explain.



When a drop punt kick is taken in AFL with a oval shaped ball, the contact between the football boot and the ball will (if done correctly) be between the lace of the boot and the underneath part of the ball at a 45 degree angle. This contact point will cause the ball to spin  due to the Magnus effect grabbing the air in the direction of the spin which in the case of a drop punt is backwards. Once the ball is now in the air it will begin to ‘lift’ as stated in Bernoulli’s principle where the force below is greater then that above as was produced by the impact force of the foot on the ball. So now that the ball is travelling upwards and spinning backwards it will travel forwards due to Newton’s 1st Law where the mass of the object is large with greater inertia so it is harder to move off its course.
In conclusion the 3 principles working together will cause the drop punt to travel straight.

But this will not always make the ball travel straight as slight changes in pressure applied by wind can cause the ball to move off course.

How Else can we use this information?

 

 

When attempting to produce a perfect movement in any skill there are biomechanical principles at play. The AFL set shot like most other forms of kicking wether it be in soccer or rugby requires a level of understanding before you are able to demonstrate the correct technique repeatedly. Through the use of this blog and similar studies you can take note of the basics applying them to your own technique to improve your selected skill. Whilst you can achieve this through means that you provide yourself to speed up the process working with a coach or trained sports Biomechanist. First step is just to begin with practice because as Ericsson theorised as referred to by David’s, Button and Bennett (2008), expertise in a skill can only be achieved after 10,000 hours of training.

 

 

References

 



Anderson, D., Sidaway, B. (2013, July). Kicking biomechanics: Importance of Balance, Lower Extremity Review. Retrieved from http://lermagazine.com/article/kicking-biomechanics-importance-of-balance
 

 

Ball, K. (2008). Biomechanical considerations of distance kicking in Australian Rules football, Sports Biomechanics, 7:1, 10-23,

DOI: 10.1080/14763140701683015
 

Brown, E. (2000). Conditions of Linear Motion. Accessed on 17.4.2012. Retrieved from https://www.msu.edu/course/kin/400/linear_motion.htm

 

 

Blazevich, A. (2010). Sports Biomechanics The Basics (2 ed.). London Bloomsbury.
 

Maslon, G. (2011). Best Foot Forward. The Melbourne Age. Retrieved from http://www.theage.com.au/national/education/best-foot-forward-20110701-1gujp.html
 

Taylor, M. (2013). Seven Principles of Biomechanical Analysis [Prezi slides]. Retrieved from http://prezi.com/sewhgcqyehfp/seven-principles-of-biomechanical-analysis/