What are the biomechanics beneficial for an AFL Drop Punt and the Torpedo?
The Australian Football League (AFL) is a dominant sport in society with many participating for health and physical activity or at an elite level. The most important means of ball travel during the game, is kicking. The drop punt is the standard kicking technique in most situations, due to a combination of accuracy, distance and speed of execution. The Torpedo is a specialised kick to increase the distance and flight time, as the ball incurs less wind resistance due to the spinning effect the ball has (AFL Community). Each participant has an individual technique, however, the fundamentals remain the same. These include; run up, plating the supporting leg, ball drop, swing of the leg, and ball to foot contact. A player’s ability to make a strong and precise impact with the ball will ultimately determine if the kick reaches the intended target (AFL Community 2017). The most common injuries in the AFL are hamstring strains, knee injuries and groin injuries and are more common on the dominant kicking side (Orchard. J, Walt. S, McIntosh. A, Garlick. D. 1999). The impact if injury will be discussed due to both participants incurring a hamstring and knee injury, hindering their optimal performance. The drop punt and Torpedo will be broken down using the biomechanics to understand the technique, and how they benefit the kicking style to achieve a greater velocity.
Key movement characteristics to be discussed:
- Run Up
- Planting the supporting leg
- Ball drop
- Swing of the leg
- Ball to foot contact
- Follow through after the kick
Breakdown of the skill:
The run up is the initial phase of the kicking action and is a crucial stage required in executing the drop punt and torpedo most effectively. Using the run up is the most preferred technique amongst players as it creates forward momentum, that is then transferred into the kicking styles, thus allowing the ball to travel further (Ball, K. 2011). Within this phase players are attempting to gather speed and momentum whilst maintaining balance to achieve the maximum potential distance of the kick. Speed and Acceleration are utilised in a linear motion to create maximum velocity potential when performing the kick. Acceleration is a vital aspect of the run up phase as it performed over a short distance of around 5-10 metres. Therefore athletes who are able to accelerate quickly will achieve a much greater level of velocity and distance of the kick, if correctly executed. In order to allow momentum to occur an impulse is required. When an athlete hits the ground with their foot, they opt to apply the largest possible amount of force for the longest time possible. The higher level of impulse achieved, the greater the change in momentum which, ultimately results in a higher velocity (Blazevich, A., 2012).
Newton’s 3rd law (ground reaction force)
Newton’s Third Law states that for every action, there is an equal and opposite reaction (Blazevich, A., 2012). The equal and opposite forces that enact when the football is kicked is the result of friction which occurs between the ball and the foot when contact is made. Gravity forces the kicks flight path to reach a particular height which, is dependent on the angle and speed of release.
Planting the supporting leg
Drop punt and torpedo kicking is a throw-like motion, with much of the work performed eccentrically in the early phases. The most active muscle group during this phase is the quadriceps and the kicking leg, which is also the wind up phase. The hamstrings concentrically initiate the backswing and show an eccentric action during the follow through (Orchard. J. Et al. 1999).
During this phase, the planting of the supporting leg is highly important for the player to remain balanced when providing momentum for the swinging leg to provide a force on the ball. Power, range of motion, balance and technique are the major factors in kicking accurately (Ball, K. 2008). It is essential that players work on either reducing or shifting the mass in their legs in order to increase the power produced. In order for this to happen players can engage in strengthening exercises concentrating on small muscle groups in an athlete’s leg (Ball, K. 2008). For example the participant in the diagram has incurred a hamstring injury resulting in the supporting leg being the dominant kicking leg. This means the player has had to shift their body mass to a non-preferred side and alter their kicking technique. The player must be able to manipulate their centre of mass. This is the point at which the mass of the player is evenly distributed in all directions, which, occurs through the hips and legs extension of the supporting leg (Blazevich, A. J. 2013). The aim of the drop punt is to propel the ball forwards in an upwards direction, as is the torpedo but due to the spinning motion of the torpedo this kick leads to the ball covering a greater distance. Momentum is transferred from the kicking foot/ankle to the ball when the angular velocity of the leg is at its maximum(Orchard. J. Et al. 1999). This is shown in the above diagram when the participant takes small steps during the run up phase, and then the planting of the supporting leg acts as a stability mechanism to maximise power and drive the ball forward.
Within the ball drop of both the drop punt and torpedo players must guide the ball down with the guiding hand cradling the ball and with the release point being at the time kicking foot leaves the ground, ultimately allowing the player sufficient time to generate power to kick the ball. The ball is released from hip level as the guiding hand controls the path and orientation of the ball. Throughout this stage the non-guiding hand is removed from the front of the ball and swings up and back in an arc to provide balance and stability. In the final stages of the ball drop it is crucial to ensure the ball is in a vertical position as it leaves the hand to allow the bottom third of the ball to reach contact with the foot. Ultimately resulting in the ball to spin backwards therefore creating a more accurate kick (AFL community, 2017).
Newton’s 1st law states that all things at rest want to stay at rest (Blazevich, A., 2012).
A player brings the ball from rest to motion by running with the football and then dropping the ball onto their foot which drives back behind the body before swinging through towards the intended target and making contact with the ball. This force then moves the ball from rest into motion towards the direction and angle that force was applied (Blazevich, A., 2012).
Kinetic energy/ Potential energy
Mechanical energy is the energy associated either with an object’s movement (kinetic energy) or its position (potential energy). Kinetic energy (KE) is defined as the energy associated with motion, therefore from a linear perspective, an object with a greater mass or velocity has greater energy. The other form of mechanical energy is potential energy (PE), which is the energy associated within an object’s position. For example a rock at the top of a cliff, if it were to roll off the cliff, it would fall with a velocity, that is, it would have kinetic energy. However whilst it is stationary at the top of the cliff, it has the potential to gain kinetic energy, potential energy (Blazevich, A., 2012). This example can be further explored within the ball drop phase. Inevitably the higher level the ball is dropped the more potential energy the ball has and therefore will achieve a higher level of kinetic energy as a consequence. As a result of the higher level of kinetic energy produced the velocity of the ball being dropped to the player’s foot will increase, therefore creating a higher potential velocity to be achieved on the ball.
Swing of the leg
During the swing phase, the leg has angular momentum. This is because any mass with velocity has momentum, and because the leg has an angle it therefore has angular momentum. As previously mentioned for optimal power and acceleration of the swing of the leg, we need to reduce the mass (shoes) or keep the mass close to the centre of rotation. this is why is why we can see the swing of the leg remains relatively close to the centre of the body to generate power for the kick.
This is how Newton’s second law is relative to this stage. The 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. In this instance the football requires a force to be accelerated at a great distance. To assist with this the torpedo can be beneficial to cover a greater distance due to the spinning effect.
Ball to foot contact
Prior to the ball making contact with the foot, the movement of the leg backwards from the front of the body needs to overcome inertia. Since the leg swings with the hip as the centre of rotation the correct term is moment of inertia (Blazevich, A. J. 2013). In this instance the moment of inertia is the distance the swinging leg is from its centre of rotation (hips). Inertia is overcome when the swinging leg changes it’s state of motion, and swings through making contact with the ball. For an AFL drop punt to be successful, players must bring their leg behind to a 90 degree angle and with a great momentum swing the leg forward to make contact with the ball and transfer the momentum to the ball, overcoming inertia and propelling the ball forward.
The ball to foot contact is a push-like movement pattern. That is all the joints extend in our kinetic chain simultaneously in a single movement. Because all the joints in the leg are acting simultaneously, the cumulative forces (torques) generated about each joint result in a high overall force (Blazevich, A. J. 2013). To improve the power and accuracy of the kick there needs to be a reduction of mass relative to the centre of rotation. Inturn this means wearing lighter shoes, and limiting strength training in the distal areas (calf muscles) (Blazevich, A. J. 2013). If there is less mass relative to the centre of rotation (hips) known as the radius of gyration the moment of inertia is decreased, resulting in an increase in the angular velocity (Blazevich, A. J. 2013). In this instance the angular velocity will be greater due to the mass being lighter in the lower leg, however there is a need for a greater momentum when the ball makes contact with the foot. In order for a force to be applied, the angle of the quadriceps and the knee joint are important when propelling the ball forward. This relates to Newton’s second law of motion in that the acceleration of an object is proportional to the mass of the object (Blazevich, A. J. 2013). Following on from this the object and in this case the football, has no momentum because it has no velocity, however it still has inertia due to a force needed to change its state of motion. When the foot makes contact with the ball the back swing of the leg and follow through are pivotal when giving the ball momentum to propel forward.
Follow through after the kick
The Kinetic chain is described by Blazevich (2012) as characteristics of push- and throw-like movement patterns and both open and closed kinetic chain movements. For human motion to occur, it requires the complex co-ordination of individual movements about several joints at the same time. In essence this creates a moving chain of body parts known as, the kinetic chain (Blazevich, 2012). There are two main categories of kinetic chain patterns: push-like and throw-like movement patterns. Kicking the drop punt is a clear example of a throw-like movement pattern as muscles around the hip accelerate the thigh before the leg and foot swing through in sequential motion, which requires correct timing for optimal performance. Throw-like movement patterns are able to make the most efficient use of the tendons. As the tendon stretches, elastic energy is stored. When the tendon is released, it recoils at a very high speed, thus a high output of kinetic energy. Throw-like movement patterns are able to achieve much greater speed and velocity opposed push-like movement patterns the recoil speed of elastic elements such as tendons is much higher than the speed of a muscle (Blazevich, 2012).
Blazevich (2012) describes the ‘Magnus Effect’ as a spinning ball ‘grabs’ the air that flows past it, due to the friction between the air and the ball and as a result the air particles begin to spin with the ball. The Magnus Effect has an affect on the drop punt as the ball spins in a backward motion in a vertical position. Ultimately this creates an increased amount air resistance and greater level of friction. Therefore the speed and velocity of the ball is significantly reduced as a result of form drag, however it does provide an increased level of control and accuracy as a consequence. This is evident as the ball spins it creates a pressure difference, which moves from left to right which in turn creates more control of the way the ball moves throughout the flight path (Blazevich, 2012). The image below provides a visual representation of the how the ‘Magnus Effect’ occurs.
The diagram above depicts a spinning ball moving throughout the air. On the left side of the ball that has air spinning around it, the ball collides with oncoming air and slows down. In contrast to the drop punt which achieves a high level of friction as it moves throughout the air, the torpedo kick is marginally influenced by friction and air resistance due to the way it travels throughout the air. The torpedo kick is a kick used to achieve large distances as it relies on a high amount of spin and rotates in a vortex position throughout the air for this to be successfully achieved.
In order to perform the drop punt and torpedo effectively, the biomechanics of the skill were reflected upon, in regards to assisting with injuries. Below is the results of the kicking progressions by the participants and after each attempt critiques were made with a noticeable improvement, with a greater velocity generated. With knee and hamstring injuries, the optimal biomechanics of the drop punt and torpedo are hindered by power, accuracy and execution of the kicking techniques. The run up phase is important for players to gain momentum, speed and acceleration to transfer this into the kick to ensure a greater distance is covered. Following on, the planting of the supporting leg allows players to shift their body mass to be evenly distributed, allowing the participant to excel power into the kick. Potential and kinetic energy is established within the ball drop phase whereas, if the player drops the ball from a greater height the greater the kinetic energy generated when in contact with the foot. However, dropping the ball closer to the foot is beneficial when avoiding wind resistance, and remaining possession.
During the swing phase speed and acceleration of the kick is important. To ensure this is achieved reducing the mass from the centre of rotation (footwear) can provide a greater velocity and power for the kick. Finally the ball to foot contact and the follow through after the kick is just as important as the lead up progressions. During this phase, moment of inertia is overcome and a push like and throw like movement pattern is generated with the movement being carried out sequentially. Although the torpedo is technically varied, the outcome of a spinning vortex (football) is beneficial when overcoming the forces of gravity and air-resistance, resulting in a greater velocity and distance achieved.
How can we use this information?
The information discussed throughout this blog may be used by coaches, players, sport enthusiasts and Physical education teachers. The information may assist coaches in providing them with the breakdown of the skill of the drop punt and torpedo kick from a biomechanical aspect. Consequently this will potentially allow coaches an opportunity to attain a higher quality output of the skill from their players, as a result of particular focus on key biomechanical aspects. Physical Education teachers may utilise this as a tool for lower grades as a skill development tool in the way skill is broken down and discussed, allow students an opportunity to better understand the skill through part task practice. Ultimately all the information presented above creates an understanding through deep analysis in regards to the fundamental biomechanical aspects utilized throughout the drop punt and torpedo kick in AFL.
AFL AusKick,. (2008). Skills – Drop Punt. Retrieved from https://www.youtube.com/watch?v=YsuzLq-n6m4
AFL Community 2017. kicking guide for players. AFL community. accessed 8th June 2017. available at: http://www.aflcommunityclub.com.au/index.php?id=878
AFL Development. (2013). Basic Mechanics of Kicking. Retrieved April 22, 2012, 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, 10-23
Blazevich, A. (2012) Sports Biomechanics: Newtons Laws, A&C Black Publishers, Bloomsbury, London, p 43-50
Blazevich, A. (2012) Sports Biomechanics: WORK, POWER AND ENERGY, A&C Black Publishers, Bloomsbury, London, p 98-108
Blazevich, A. J. (2013). Sports biomechanics: the basics: optimising human performance. A&C Black.
Orchard. J, Walt. S, McIntosh. A, Garlick. D. 1999. Muscle activity during the drop punt kick, sports science journal. accessed 8th June 2017. available at: http://www.johnorchard.com/resources/article-muscleactivitydroppunt.pdf
Rath, D. (2005). Biomechanics of Kicking. unpublished Hawthorn Football Club. Available at: http://www.ulstergaa.ie/wp-content/uploads/2008/01/biomechanics-of-kicking-taken-from-afl.pdf
Victoria University, The Conversation, Centimetre Perfect: A quest for flawless goal kicking in the AFL, Melbourne