Major Question

What are the optimal biomechanics for a drop punt in AFL?

Australian Football is one of the country’s most popular spectator and participant spots. Considering this the biomechanics of its techniques have not been extensively studied. The most common use of ball disposal is the kick, specifically the kicking technique of the drop punt, due to a combination of accuracy, distance and speed execution (Orchard et al. 2002). The object of the drop punt kicking is to project the ball accurately over a desired distance at a desired velocity (Dichera et al. 2006). This ability allows for goals to be scored at long distances and with the increasing defensive pressure in the forward 50, players are able to take a shot on goal further out from the forward line.  Effective long kicks during a game have been found to be a major predictor in score difference between AFL teams (Forbes 2003). The punt kick is important throughout a game of football, but the support leg kinetics and ground reaction forces have been implicated in injury and performance in kicking (Ball 2013), this is why it is critical to determine the optimal biomechanics to enhance performance and limit injury.

Many different biomechanical principles can be used to improve the technique of the drop punt kick. Although players’ individuality will have slightly different preparation techniques, the biomechanical principles discussed in this blog should be able to be applied to the majority of drop punt kicking techniques.

Within this blog these biomechanical principals will be explored:

• Impulse-momentum
• Acceleration
• Newtons Three Laws of Motion
• Levers
• Ground reaction force
• Centre of mass

The Answer

The drop punt kick is divided into five specific stages that can be broken down to discuss the biomechanical factors affecting each action.

The skill cues of the drop punt are shown in figure 1, and includes the:

• Approach
• Release
• Support land
• Ball contact
• Follow through

Figure 1. The drop punt kick sequence (Ball 2008)

The run up approach and foot speed: Australian rules football requires high level of technical expertise, tactful awareness, speed, power (force), accuracy and endurance in a fast-moving environment (Hart et al. 2014). Therefore, impulse and momentum are two key biomechanical factors that are used in the drop punt kick. Blazevich (2010) defines impulse as “the product of force and time” and momentum as “the product of mass and velocity”. Therefore, to increase the momentum of the football the impulse needs to increase.

In order to increase the momentum of the football, the impulse force of the kicking foot has to increase. Newtown’s second law states that, the relationship between an objects mass m, its acceleration a, and the applied force F is F =ma. Acceleration and force are vectors, in this law the direction of the force vector is the direction of the acceleration vector (Blazevich 2010). The most efficient way to increase the momentum of the football is to increase the acceleration of the foot prior to making contact. It is important to know that the foot speed is not the speed of the food during the run up or approach but the speed when the foot travels through the air prior to contact. Prior to the kick using a six to eight step run up, the last 0.2 seconds of the approach were designated to the push off period. Step length throughout the run up has no effect on the kicking performance but a longer last step has been associated with greater kicking distance. The longer last step may allow for greater hip extension and thigh range motion, which in turn increases the potential for developing greater foot speed (Ball 2008).  As seen in Figure 2 Ball (2008) found that when kicking for distance, a greater foot speed metres per second was favoured.

Figure 2. Studies involving multiple kickers and attempts.

In the research of Ball (2008) the force production, forward swing of the foot speed at ball contact 26.4 m/s kicked the ball 61m. The forward swing is the phase of continued hip flexion and knee extension which lasts 0.05 seconds and ends at ball contact. At ball contact the right knee (preferred kicking side) is still flexed at approximately 50 degrees, with the support leg moving forward with an angular velocity of approximately 1400 degrees per second with the right ankle held fixed in plantar-flexion (Orchard et al. 2002). Greater hip flexion allows for a fluid movement and a greater hip flexion throughout the movement also has links with greater accuracy (Dichiera et al. 2006).

The support leg: The support leg acts as the base of support and allows for the body to prepare and balance for the momentum from the kicking leg. Ball (2013) found that the support leg kinematics was related to punt kicking performance. A more extended knee at support leg foot strike that remained at a greater extension (lower maximum flexion) during the stance phase was related to greater foot speeds at ball contact (Ball 2013). This could indicate that a stronger support leg is valuable aspect of an elite athlete. The strong supporting leg assists in the extension for the player to be able to kick through the football. Diagram 1 below illustrates the role of the supporting leg in three phases, the flexion, absorption and extension. The flexion and extension phase of the supporting leg is where the momentum shifts due to ground reaction forces (Orchard et al. 2002). Ground reaction force is when the force exerted by the ground onto a body that is in contact with it (Blazevich 2010). The ground reaction force pushes the body up, with the follow through and momentum pushes the kicking leg up that was in contact with the ball, which can contribute to greater force behind the kick.

                                                Flexion              Absorption         Extension

Diagram 1, The three stages of the supporting leg throughout the kicking motion.

The ball position and release in relation to the guiding arm: The centre of gravity and linear motion is vital in the drop punt kick. Linear motion can occur either in a perfectly straight line (rectilinear motion) or a curved line (curvi-linier motion) (Blazevich 2010). The ball is held with both hands evenly spreading the fingers over the ball, the ball was released by the left hand (when a right foot kick is being executed) prior to the “push off” movement and then released by the right hand at about waist height. This decreases the amount of space between the ball drop and the kicking foot to allow the ball to move in a linear motion and also keep the core and centre of mass of the player upright to keep the body in balance. The centre of mass is the point at which the body is evenly distributed in all directions (Blazevich 2010).

Newtons third law of motion “for every action there is an equal and opposite reaction” applies somewhat to the guiding arm of the drop punt (Blazevich 2010). As the right foot player releases their ball grip from the left hand, the right hand guides the ball onto the foot and the left hand swings out from the body. This counteracts the swinging motion of the right side of the body to keep the body evenly distributed, and the players’ centre of mass balanced. This is shown in the Youtube video below of Nathan Buckley, where through the kicking motion Nathan releases his left hand from the ball and moves it outside of his body with a follow through to the intended target of the kick.

Ball Contact and follow through: It is noted that the kick knee of the player extends prior to contact with the ball, stabilizing the movement (Ball 2013). Levers are used in all sports and in AFL the legs act as levers. The knee of the player acts as the fulcrum or the point of rotation of the lever moving in a forward motion from behind the players body, resulting in resistance (Hede et al. 2010). The legs are third class levers and are efficient in generating speed and range of motion which creates more force. The leg moving forward generates a positive acceleration (Blazevich 2010). Understanding acceleration can have positive benefits for individual and team sports. To ensure maximum force and acceleration transfers into the football to increase kicking distance and efficiency it is important that the leg is straight at the point of contact to produce a follow through and forceful knock on effect. This is in correlation with Newtons First Law of Motion that “every object in a state of motion tends to remain in that state of motion unless an external force is applied to it” (Blazevich 2010).

The follow through and recovery starts at the initial ball contact and finished at the hip maximum flexion, 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 et al. 2002). This creates a force of momentum upwards prior to landing again due to gravitational forces.

How else can we use this information?

Research found that greater accuracy was linked with greater pelvic tilt, and hip and knee flexion (Dichiera et al. 2006). An increase in the final step of the run up is recommended but should be monitored carefully to determine an optimal point for each individual, as if the ball is dropped to far out in front, the player will be reaching decreasing the level of force behind the ball, or if the ball is too high the ball trajectory will be too vertical (Ball 2011). According to Ball (2013) conditioning the support leg to maintain a more extended knee position and to produce greater breaking forces may assist in players to attain a stronger base of support for kicking which in a game of AFL can have positive outcomes. To increase the kicking distance in AFL it is recommended to increase the speed and shank angular velocity at ball contact (Ball 2008).

This information would be useful for football coaches and players who would like to attain the most effective drop punt technique to achieve positive outcomes. This information provided in this blog is a good starting point for understanding the biomechanics of the drop punt kick in AFL or as a part of a teaching curriculum. Educators will benefit from this blog with the need to understand biomechanical principles, how they are put into action and to assist in explaining and answering questions in regards to the importance and key points of the skill.

There are several other sports that the biomechanical factors of the drop punt kick discussed in this blog can be related to. The drop punt kick can be related to many kicking sports including American Football, Soccer and Gaelic Football and can benefit from this information.  

Although there are these principals for the optimal technique it should be noted that an elite athlete can take these into consideration but may also have their own techniques and application of skill that works for them and what feels comfortable to the athlete is supported.

The result of using this information and executing optimal biomechanics? A full force, long distance, accurate kick.

References

Blazevich, A. (2010). Sports biomechanics, the basics: Optimising human performance. A&C Black

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

Ball, K. A. (2011). Kinematic comparison of the preferred and non-preferred foot punt kick. Journal of sports sciences, 29(14), 1545-1552.

Ball, K. (2013). Loading and performance of the support leg in kicking. Journal of Science and Medicine in Sport, 16(5), 455-459.

BigPondAFL. (2012, August 2012). Tom Hawkins goal on the siren - AFL [Video file]. Retrieved from https://www.youtube.com/watch?v=2h9OVHIGNAE

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.

Forbes, D. (2003). Characteristics of match statistics in the AFL. Melbourne: Swinburne University/Champion Data Research.

Hart, N. H., Nimphius, S., Spiteri, T., & Newton, R. U. (2014). Leg strength and lean mass symmetry influences kicking performance in Australian Football.Journal of sports science & medicine, 13(1), 157.

Hese, C., Russell, K., & Weatherby, R. (2010). PE: Senior Physical Education for QLD. Queensland: Oxford University Press.

Orchard, J., Walt, S., McIntosh, A., & Garlick, D. (2002). Muscle activity during the drop punt kick. Science and football IV, 32-43.

Warchief100. (2010, September 7). How To Do a Drop Punt [Video File]. Retrieved from https://www.youtube.com/watch?v=aj1fGrHTls8

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