What are the crucial biomechanical principles involved with kicking for goal during a set shot in Australian Rules Football?

Introduction

Australian Rules Football (AFL) is a microcosm of Australian society, where culture is reproduced and values are common nation-wide (Fitzen and Sage, 1989). AFL provides prospect for individuals to become physically fit as well as providing an opportunity for social integration in an invasion game (Tonts, 2005) (Pill, 2013). Biomechanics is the field of science devoted to understanding mechanical principles in relation to biological organisms (Blazevich, 2012). Biomechanical techniques have been established in AFL and although optimal techniques have been reached, there are still varying techniques when attempting a shot on goal, however the fundamental movement patterns remain the same to achieve a successful kick (Aflcommunityclub.com.au, 2015). Which can be seen through many modern day players including Drew Petrie and Daniel Rich.

The biomechanics of the AFL set shot kick refers to the movements specific for the application of the sport. The action of goal kicking is a complex combination of accuracy, power, strength and flexibility. Each of these components is a part of small complex movements, which the force summations synchronize and allows the ball to be struck in desired fashion (Blazevich, 2012). The set shot for goal is a perfect example of this and, when performed perfectly is one of the most exciting aspects of the game.

The following biomechanical principles will be included during this blog:

Accuracy- the degree to which the result of a measurement, calculation, or specification conforms to the correct value or a standard.

Angular momentum- product of the moment of inertia and angular velocity; angular analogue of linear momentum.

Angular velocity- the rate of change in angular displacement; equal to angular displacement per unit time.

Balance- an even distribution of weight enabling someone or something to remain upright and steady.

Distance- sum total of displacements of an object without reference to resultant direction.

Inertia- tendency for a body to remain in its present state of motion.

Impulse momentum relationship- relationship between impulse and momentum; the momentum of an object will change in proportion to the sum of a applied impulses.

Newton’s First Law- very object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

Newton’s Second Law- the relationship between an objects mass (m), its acceleration (a) and the applied force (f) F=ma. Acceleration and force are vectors. In this law the direction of the force vector is the same as the direction of the acceleration vector.

Newton’s Third Law- for every action there is an equal and opposite reaction

Projectile motion- object in free motion subjected only to the forces of gravity and air resistance

Torque- a twisting force that tends to cause rotation.

(Definitions of the biomechanical principles were taken from Blazevich, 2012)

Goal kicking

Figure 1. The Drop Punt Kick Sequence (Ball 2008)

The major skill required for playing Australian Rules Football (AFL) is kicking, players need to learn the critical elements of kicking before applying the same principles when kicking in front of goal (AFL Community, 2012). The key to being able to kick well is having a sound basic technique, although individuals will find a slightly individual technique that is suited to them, there are a few basic biomechanical principles that are evident throughout. Goal kicking uses the key principles of accuracy, distance, impulse momentum relationship, projectile motion and Newton’s three laws (Blazevich, 2012).

These key principles can be seen in both links attached below.

Gary Ablett on Goal kicking

https://www.youtube.com/watch?v=OD9ci2Ovxmw

Gary Lyon and Matthew Lloyd on kicking

https://www.youtube.com/watch?v=gdRfAFBEj-M

Run and Approach

The run and approach phase of goal kicking is where the player gains momentum as a steady controlled movement prior to kicking the ball. The player should have their hips square with the goals and be facing their target in order to achieve angular velocity through force summation ultimately transferred to the ball. The speed and momentum the athlete is able to gain is then translated into horizontal velocity, which can be seen after contact has been made with the ball. Therefore the run and approach section is a critical part of goal kicking in AFL. Ideally, the player will reach a steady speed whilst running directly at the goal, at an appropriate distance from the man on the mark in order to be successful with accurately kicking a goal.

Newton’s First Law states, “an object will remain at rest or continue to move with constant velocity as long as the net force equals zero” (Blazevich, 2012). The run and approach phase is a key part of goal kicking as it allows the athlete to gain momentum for a combination of accuracy and distance. The mass of the player also adds to the momentum, therefore players with larger body mass will not need to have a run up that is quite as fast in order to have a similar output, but will biomechanically be at an advantage with a faster run and approach phase (Blazevich, 2012). The player applies a force larger than the present inertia, resulting in an increased running speed on approach to the kick. Leading to Newton’s Second Law that 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, 2012).

Although, distance from goal can be a problem and if the player is beyond their range, a curved arc run and approach is common among current AFL players. This allows the players to gain more momentum and therefore gain more distance from their kick, although statistically, this has proved to not be quite as successful in scoring the desired result. Although it should be noted that the same correlation between distance and accuracy can be seen in sports world wide, as the further from goal, it is naturally harder to score.

Grip and Ball Drop

Figure 2. grip of drop punt (NAB AFL Auskick, 2012)

By referring to Figure 2 you can see that the hands are evenly distributed across both sides of the ball this is so when the ball is dropped it is kicked on the base of its longitude axis, when the football is being guided down by the kicking foot sides hand (right hand for a right foot kick) the kickers other hand will come off the football and be swung out, this is basically for balance (see videos above). While this is occurring the other hand will guide the ball towards their kicking foot and let go of the ball on the up to create a bigger range of motion for distance in the kick, this will be specified more in the next phase. By doing this it will allow for gravity to have its effect on the ball by forcing the ball to the leg which will later extend at the knee to come into contact with the ball (Blazevich, 2010). When performed properly this aspect of the kick requires inertia which is key element of Newton’s First Law, in this specific setting inertia ‘allows the ball to remain in its state of rest until released, at this stage gravity causes the ball to drop and continues with a consistent angular velocity” (Blazevich, 2012). When the ball is kicked the ball should be contacted on the base of the ball’s longitude axis on the laces of the player’s boots, this is so it creates a backward spinning motion on the ball while it stands up in a vertical manner, this creates a Magnus effect on the ball which will be discussed later, this allows the ball to travel the required distance (over the goal line) by travelling through the along the correct projectile motion.

Generation of Speed through opposing leg

(Pedler, 2012).

While this component of the drop punt kick is a phase that happens much quicker than the previous phase, it is an important aspect of how powerful and accurate the kick is going to be to reach its target. The force generated on the ball should be enough to enable it to gain appropriate distance to travel over the goal line without being touched by an opposition player. The actual speed of the kicking foot is created through the leg swing or the ‘wind up’ phase. Velocity is generated through a slight knee bend, which you can see in Figure A above, before it lengthens and swings towards the football, as shown in Figure B above (Blazevich, 2010). To get optimal distance from the kick the moment of inertia must be reduced, this will occur by producing tight angles at the thigh (see figure B) and the shank angle (see figure B), as the kicker springs vertically from the momentum of the run up and approach (Ball, 2008). To also increase the distance of the kick they need to create a larger range of motion and have higher flexibility in the hips, as seen in Figure A but even to a greater extent. To help this phase and the reason for the ball to travel further is with the help of angular impulse. As suggested by Blazevich (2012), angular impulse is created by employing a force over a higher extent of time. By expanding the range of motion in the hips in the wind up phase (see figure A), the player will employ torque, force for an extended period of time, which will increase angular velocity in the leg and produce a higher angular momentum when the leg moves back towards the ball which will result in more power behind the leg and result in the ball travelling further (over the goal line). The opposite leg is mainly for balance as it bends (see figure B) and soaks up the force from the momentum.

Contact and follow through

Daniel Rich (Brisbane Lions) is one of the best long kicks in the AFL (Hub Pages, 2015)

Drew Petrie (North Melbourne) has a very straight and accurate kick (Hub Pages, 2015)

During the actual kicking contact stage of the drop punt the player needs to equally spread their centre of mass, to allow for a larger support base (Blazevich, 2012). This is done by the supporting leg’s pelvis rotating and the head being in line with the supporting leg’s foot (Rath, 2000). While this is happening the angle of the support leg knee is marginally tensed, to lower their centre of gravity which will further enhance stability (Dichiera et al, 2006). When making contact with the football pointed toes and flexed leg muscles are vital to guarantee the foot has a greater contact surface area. If these fundamentals of kicking are not present there will be less energy going through the ball, therefore less speed, and will not reach the distance over the target (over the goal line).

As Newtons third law declares that for ‘every action there is an equal and opposite reaction’, this can be said how the ball reaches its intended target (over goal line) because of the force being applied from the momentum created (Blazevich, 2012). The foot has the allocation of transferring the velocity produced into the ball, but is reliant on the quality of the actual contact (Ruth & Young, 2011). Cross (2010), suggests that a football’s coefficient of restitution is usually 0.8, which with basic mathematics suggests that 80% of the initial energy produced will remain through the football after the force is applied. The ball will then leave the kicking foot and continue to spin backwards in an upright backwards manner, by incorporating this spin on the ball it allows the ball to hang in the air for a longer period of time and get the correct trajectory path for the ball to go over the line. The ball is able to sit up in the air for longer because of the Magnus effect, the air flow going past the ball will be evenly distributed on both sides of the ball (Knudson, 2007), and this will only occur if the player kicks the ball on the point by creating a large surface area as stated above. After making contact with the ball it is important to follow through as it can also help with the performance of the kick and also injury prevention. This can be done by the player swinging their kicking leg high and really stretching out after kicking the ball, by doing this it helps gradually disperse the momentum that has been made from the previous phases in the kinetic chain (Blazevich, 2012), because if the players body was to rapidly come to a halt it would put a lot of tension on their muscles and ligaments trying to combat the built up momentum. The injury might not occur on that particular kick but if continued over time would be more likely to happen.

Ball contact, follow through and foot speed

The most basic part of teaching to kick is to start with the impact of the foot connecting with the ball. Every kicking technique and every kicking situation is different; therefore a focus on grip, approach and follow through is not as important as what happens at impact. Players will learn to evaluate their kicking to the game situation they find themselves in. Situations in a match may mean the player doesn’t have time to grip the ball in a certain way, they may have to kick off one step or produce a low flat kick that produces a little follow through (AFL Community, 2012).

A player’s ability to make strong contact with the ball will ensure the kick reaches the intended target, in this case, the goals. Goal kicking has angular momentum and Newton’s 3rd law as key principles; for every angular action there is an equal and opposite angular reaction. Angular momentum is increased when the large step before kicking occurs, which allows the kicking leg to be a strong powerful use of momentum in order for maximum distance when kicking for goal (Blazevich, 2012)

The follow through phase of the kick starts at the initial ball contact and finishes at the maximum point of hip flexion. For a player kicking with their right foot, the right hip continues to flex during the recovery part of the follow through for approximately 0.2 seconds after the right knee finishes extending (Orchard, 2012). This creates a summation of forces allowing for more distance on the kick and upwards power causing the player to ‘hop’ before landing due to the gravitational forces.

Answer

Kicking a drop punt for goal in AFL football many biomechanical principles can be discussed and be broken down into certain components such as Run and Approach, Grip and Ball Drop, Generation of Speed through opposing leg, Contact and follow through in order for the player to kick the ball accurately and with enough distance in order for the ball to travel over the goal line. In order for this to occur the biomechanics suggest that the player should have a straight run up, running directly towards the intended target (goals), the player must run at a comfortable pace, not too quick as this will affect their balance, by doing this the player will gain momentum to continue and help with the next component. From a biomechanical perspective it is well documented that force = mass x acceleration but in this situation the mass cannot be changed, so for in order for the football to travel further and the required distance, the acceleration must be increased. This can be done by twisting your hips to create a larger range of motion to allow your kicking leg to have a greater distance to travel before making contact with the football, this will allow the player more time to create angular velocity, therefore generating more angular momentum and angular impulse. By having these biomechanical principles present or altering your technique to allow them to become greater will generate a higher summation of forces, which means when the football is come into contact the foot speed will be greater (acceleration) and therefore the ball will travel the required distance (over the goal line). The ball will be kicked underneath the ball to produce a backward spin and a Magnus effect with the air evenly distributed across both sides of the ball. The player will then finish off the kick by following through as this will help with the power of the kick and less likely to cause injury.

How else can we use this info?

The information discussed above can be used by anybody but would be extremely beneficial to football coaches or Physical Education teachers who are trying to educate the athletes on an AFL drop punt kick for goal. The teacher/ coaches can use the biomechanical principles to breakdown the skill to ultimately improve a player’s kicking technique. Despite this different players are going to have different techniques for certain biomechanical principles, if it feels comfortable for you and is effective and most biomechanical principles are met then their technique should not be tinkered with. These techniques and biomechanical principles do not just relate to the AFL drop punt kick, it can relate to other sports that require kicking, such as soccer, gridiron and rugby, even though certain movements might differ slightly and the ball is a different shape and size, the main biomechanical principles will stay apply. Every biomechanical principle once understood in regards to the drop punt kick can be taken away and incorporated into other sports, for example if moment of inertia and torque is looked at from a running perspective and the sprinter has a quicker leg swing with extra angular momentum they will become faster, which is ultimately their goal. Games that involve striking a ball could use acceleration to understand that for the ball to travel further, such as past the fielder in cricket to reach the boundary, more acceleration and force needs to be applied for this to occur, which can be done by allowing the player more time between the beginning of the drive and when they finally make connection with the ball.

References

Aflcommunityclub.com.au,. (2015). AFL Community: Basic Mechanics of Kicking. Retrieved 7th June 2016, from http://www.aflcommunityclub.com.au/index.php?id=424

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

Blazevich, A. J. (2012). Sports Biomechanics: The basics: Optimising human performance (2nd ed.). London: Bloomsburry Publishing.

Cross, R. (2010). Bounce of an oval shaped football. Sports Technology, 3(3), 168-180

Dichiera, A., Webster, K. E., Kuilboer, L., Morris, M. E., Bach, T. M., & Feller, J. A. (2006). Kinematic patterns associated with accuracy of the drop punt kick in Australian Football. Journal of Science and Medicine in Sport, 9(4), 292-298.

Hub Pages,. (2015). How To Kick An AFL Football Further. Retrieved from http://hubpages.com/sports/How-To-Kick-An-AFL-Football-Further

Knudson, D. (2007). Fundamentals of Biomechanics. USA. Springer

NAB AFL Auskick. (2012). Auskick Skills Guide. Retrieved from http://mm.afl.com.au/portals/0/afl_docs/development/coaching/junior_manual/AFL_Junior_Coaching_Manual_5.pdf

Pedler, A. (2012). The biomechancis of the drop punt: three-dimensional kinematics, variability and muscle activity. Unpublished PhD thesis, University of South Australia - Adelaide.

Pill, S. (2013) Play with Purpose (edn 3) ACHPER. Australia

Rath, D. (2000, December). Biomechanics of kicking. Presentation. Australian Rules Coaching Course. Amsterdam, Netherlands

Young, W. B., & Rath, D. A. (2011). Enhancing foot velocity in football kicking: the role of strength training. The Journal of Strength & Conditioning Research,25(2), 561-566.

Tonts, M. (2005). Competitive sport and social capital in rural Australia. Journal of rural studies, 21 (2), 137-149