Introduction
The following principles will be explored;
Linear momentum
Linear velocity
Throw-like movement patterns and push-like movement patterns
Force
Angular velocity
Angular momentum
Center of mass
Linear velocity
Throw-like movement patterns and push-like movement patterns
Force
Angular velocity
Angular momentum
Center of mass
What are the optimal bio-mechanics of an AFL drop punt used for distance?
To evaluate the optimal biomechanics it is important to note that we will be investigating a professional footballers kick. But what constitutes as 'optimal'? In order to evaluate the drop-punt successfully, the following movement characteristics have been noted as key attributes to kicking success (Millar, 2004) and will be used to assess success.
The key movement characteristics successful to an optimal drop-punt are:
- A long backswing (position of hip extension and maximum knee flexion).
- An upright body position during the kick.
- The path of the foot should come through in a straight line in the direction of the kick.
- Watching the ball all the way onto the foot.
- Holding the ball straight as it is released from the hands.
- A taut instep. The ankle should be fixed in a position of plantar-flexion so that the ball will contact the bony surface of the foot.
- Foot to ball contact should not be too high off the ground.
(Other important notes to mention are that the players used in the following demonstrations are physically strong and healthy, have a full range of motion, have no injuries and are experienced with their kicking techniques.)
The following video is an example of how to correctly kick a drop-punt kick presented by former Collingwood AFL player Nathan Buckley. This video will help present a visual representation of a drop-punt kick.
What are the essential movement sequences of the drop punt kick?
The drop-punt kick can be broken down into the following 5 phases;
Phase 1: Approach
Phase 2: Supporting leg
Phase 3: Ball drop
Phase 4: Leg wind up and foot speed
Phase 5: Contact and follow through
These phases link together and optimally form a kinetic chain, a term used to describe the sequence or chain of events to form a movement.
Phase 1: Approach
Figure 1: Hand grip position
The approach consists of all the lead up movements. This includes the grip (figure 1), hand position and run-up. The first step in the approach is vital as it begins the state of motion known as horizontal velocity. The horizontal velocity enables momentum to be transferred into the impact of the ball in phase 5: contact (Ball, 2008; Ball, 2011 & Blazevich, 2012). In order for this state of horizontal velocity to begin, the individual must push and lift their foot from the earth. This is a direct link to Newton's 3rd law of motion, "every force has an equal and opposite reaction force'. A vertical and horizontal force is applied to the earth as the foot makes contact with the ground (figure 1). The ground then exerts a ground reaction force, which helps stop our feet from sinking into the earth and by accelerating us forwards, if the force is large enough to overcome our inertia (Blazevich, 2012).This is demonstrated in figure 2, as you can see the driving action of the left foot into the ground produces an equal and opposite ground reaction force.
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| Figure 2: Ground reaction force |
As demonstrated in figure 3 below, the individual prepares to kick the football with their trunk in a slight forward position. Creating this forward position allows the individual to balance, whilst still enabling force and a greater range of motion to be achieved. Following these optimal biomechanics of the approach, the player can then achieve: "An upright body position during the kick" and "A taut instep. The ankle should be fixed in a position of plantar-flexion so that the ball will contact the bony surface of the foot" (Millar, 2004).
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| Figure 3: The approach |
Phase 2: Supporting leg
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| Figure 4: The supporting leg involves flexion, absorption and extension throughout the kick. |
The supporting leg does exactly as it intends,
to support. As the kicking leg lifts off of the ground and into its full
extension movement, the supporting leg must maintain balance and support
the torso of the player from becoming unstable. It is also essential that
the player can manipulate their center of mass from the center of their body
over to the non-kicking leg. This helps increase balance and range of motion,
as the non-kicking leg acts as a pivot point for the kicking leg to swing back
further (Ball, 2011). The supporting leg has also been associated with
maintaining a technical hip alignment so that the ball can travel straight
and long (Orchard, Walt, McIntosh, & Garlick, 2002). As seen in the figure
above (figure 4), the supporting leg during a drop punt involves flexion
and extension through the knee. This helps the follow through of the
kicking leg push the ball to a greater distance as force is increased when
flexion of the knee extends and the heel of the supporting leg has been lifted
off the ground (Orchard et al., 2002). A slight plantar-flexion also
occurs at the ankle joint. This helps supports the foot during the kick and
enables the player to push away from the ground, assisting with vertical lift
in the kicking foot. This principle can increase the force from the football
impact slightly which can assist with kicking distance. Having a strong
supporting leg helps the body absorb the momentum that is established
through the swing of the kicking leg and assists the player in forming a sturdy
leg backswing.
Phase 3: Ball drop
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| Figure 4: Ball drop |
The
ball drop involves the moment in which the player drops the ball to their foot
to kick (figure 4). During the ball drop of the drop-punt the non-dominant hand
leaves the ball allowing for a slight rotation through the hips and shoulders
to occur. This increases kinetic energy of the football as a greater mass is
put directly behind the ball, in this case, the kicking leg. This is a product
of mass x velocity. The rotation of the torso causes a greater proportion of
mass behind the ball and in theory a greater mass has a greater kinetic energy
output, as per the equation. Therefore, the non-dominant hand plays an
important role in rotating the torso and increasing kinetic energy transferring
to an increase in overall distance. The non-dominant hand has another important
aspect as when it leaves the ball, it acts as a counteract to the swinging
motion that occurs from the kicking leg, this keeps the body evenly distributed
and in other words, the non-dominant hand allows the players to balance their
center of mass. Following the movement patterns
of the non-dominant hand in the ball drop. The most important aspect of the
drop punt is the drop of the football onto the boot. If the ball is being
kicked on the right foot, the right hand of the athlete becomes the dominant
guiding hand, which will then drop the ball vertically over the
kicking leg whilst being dropped at hip height. This allows the
athlete to make contact with the bottom third of the ball which makes an
effective drop punt, due to the ball spinning backwards (AFL Community, 2016). This
allows the ball to travel further caused by the Magnus effect, which
explains that a ball travelling backwards in the air will cause the ball to
stay in the air for longer and travel further, as a ball spinning forwards will
see the ball to drop quick than usual due to air resistance and gravity
(Dooghin, Kundikova, Liberman & Zel'dovich, 1992). As the
player drops the ball, the trunk shifts from a slight forward position to a
small backwards lean as shown in figure 5. This permits the ball to be dropped from hip height,
which is the recommended height for ball release (AFL Community, 2016). This
trunk position is ideal and allows a greater time/distance between the ball
drop and kick for the ball to be guided by the hand, allowing for a greater
accuracy to occur within the kick as the
longer the contact time in the ball drop, the more control the player will
have. Looking at figure 5, we can also see that the player makes continuous eye contact with the ball during the drop phase. This is essential for accuracy of the follow through foot. Following these optimal biomechanics of the approach, the player can then achieve: "Watching the ball all the way onto the foot" and "Holding the ball straight as it is released from the hands" (Millar, 2004).
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| Figure 5: Past professional AFL footballer Daniel Bradshaw (Brisbane Lions) performing a drop punt kick. |
Phase 4: Leg wind-up and foot speed
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| Figure 6: leg wind-up and foot speed |
During the initial wind-up phase of the drop-punt kick a throw-like movement pattern occurs due to the joints being extended sequentially, one after another. A throw-like motion can be characterised by a proximal to distal sequence of movement. This is demonstrated as the muscles around the hip extend and accelerate the thigh, before the knee and ankle swing through during the kick. Notice in the circled picture above (figure 6) how the knee is bent in flexion for the majority of the movement. Upon extension of the knee the patella tendon is stretched during flexion and the stored elastic potential energy is released to recoil and achieve a force multiplication effect. This effect can be compared to a sling-shot that uses elastic to propel rocks rather than trying to throw them (Blazevich, 2012). This promotes high velocity and an increase in foot speed. Having a bent leg conserves angular momentum in the leg wind-up, translating into a faster delivery of the kick (Blazevich, 2012). During the contact phase of the kick the joints in the kinetic chain of the leg all move simultaneously in a single-movement resulting in a straight-line movement of the chain, in this occurrence the foot. Therefore, the extended leg is moving in a push-like movement pattern. This results in better accuracy and cumulative force that increases the distance of the drop-punt kick. Following these optimal biomechanics of the leg wind-up and foot speed, the player can then achieve: "A long backswing (position of hip extension and maximum knee flexion)" (Millar, 2004).
Phase 5: Contact and follow through
When the
football player has made contact and followed through with the ball. The kinetic
chain changes from a throw-like movement pattern to a push-like movement
pattern. The joints in the kinetic chain all synchronise as one single
movement through the kicking leg. This builds and increases greater torque in
each joint, resulting in a larger overall force. Therefore, a longer distance
can be produced as well as an improvement in accuracy, as the ball is being
pushed towards a directed target with all joint rotations moving in a
linear line at the conclusion of the chain (Blazevich, 2007). Upon making contact with the ball the body is affected by both
velocity and mass, in other words 'momentum'. The action of the kick requires
the body to be propelled forward and in turn momentum is transferred forwards
to the ball. This allows the individual to increase the overall distance
of the kick, as the speed of the ball is also increased through the
momentum transfer. It is equally critical to extend the leg in the contact
phase to take advantage of an increased moment of inertia, as well as an equal
and opposite reaction force to translate into the kicking leg. This is
demonstrated in figure 7 below; as one ball hits another, the momentum is
transferred to the other ball and propels it forwards.
This is also very important
during the final stage of the kick, the follow through. During the follow
through, the player will have shifted most his weight over to the non-kicking
leg while completing the sequence and making contact with the ball. This allows
for a full swing of the leg to follow through this stage of the sequence,
maximizing the player’s range of motion and kicking truly through the ball. The
kicking leg in this phase comes through in a straight line due to linear
momentum and enables the ball to be propelled forwards with maximum force and
to its desired target. The foot makes contact with the ball at knee height,
which is relatively low to the ground; this ensures that the leg is at its
maximum velocity as it is at its peak of inertia. It is also essential that the
ball make contact with the ankle joint, or ‘hump’ of the foot. Any further down
the foot will result in impact with the slender foot bones, and will result in
a less stable platform, less efficient contact and an increase in potential injury.
Following these optimal biomechanics of the leg
wind-up and foot speed, the player can then achieve:
"The path of the foot should come through
in a straight line in the direction of the kick" and "Foot
to ball contact should not be too high off the ground" (Millar, 2004).
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| Figure 7: Momentum is transferred from one ball to another as they make contact with each other. |
The distance the ball carries in the air is effected by horizontal and vertical velocities of the AFL football and the height at which the contact has been made with the ball above the ground surface (Enoka, 2002). As you can see from figure 8, an object struck from the ground has a optimal projection angle of 45 degrees for maximum distance. As an AFL football is struck slightly off of the ground surface the optimal projection angle is slightly decreased under 45 degrees to reach its maximum distance. A drop punt kicked at and larger angle i.e. 75 degrees, will cause the ball to hang in the air longer and decreases the distance of the kick where as a drop punt kicked at an angle of 20 degrees will give the ball not enough air time with a horizontal velocity causing the ball to drop short.
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| Figure 8: Optimal angle for distance |
Other considerations
For optimal biomechanics to occur, considerations such as equipment, footwear and body composition should also be taken into account. A football that is wet or greater in size/width increases the mass of the ball and therefore requires more force to accelerate, whilst a ball with a smaller mass will require less force to accelerate. This can be referred to as Newtons 2nd law as “The change in velocity (acceleration) with which an object moves is directly proportional to the magnitude of the force applied to the object and inversely proportional to the mass of the object.”The muscular build of an individuals lower limbs e.g. larger quadricep muscles, can generate more force resulting in greater distances. Football boots not allowing full plantar-flexion to occur can affect the foot speed and in turn decrease the maximum distance achievable. Although these considerations are not classed as human biomechanics, they are optional principles that can be explored to benefit individuals and increase the biomechanics principles. Further research is needed for conclusive results.
How can we use this information?
You could use this information for any football players or coaches wanting a greater understanding and application of the key biomechanics that are involved in a successful AFL drop punt. This information provides justification and rationale behind important bio-mechanical principles that are required and can be put into practice to improve kicking technique and distance. It is important to note the backbone behind any successful kick is technique. The examples provided have demonstrated certain aspects of the skill as well as the techniques required to perform them effectively. Biomechanics can have a large role in preventing injury as well as benefiting from performance enhancing to improve distance and accuracy in the drop punt for footballers. Coaches can use a biomechanical analysis from videos taken of the athlete performing the acquired skill to determine what parts of their kicking technique can be changed to reduce movement variations which are causing injury and also adapt certain techniques so that the athlete can increase their kicking performance for optimal distance (Making Stridz, 2016). A coach or trainer can dissect and evaluate kicking techniques step-by-step using the 6 essential phases that have been broken down in-depth. By analysing the drop punt used in Australian rules football we can look at other kicking sports that have similar bio-mechanical principles and factors, e.g. soccer, rugby, gaelic football etc. We can apply the same principles directly to those sports and transfer information and knowledge. The principles discussed are related to optimal technique, however it should also be noted that individuals can still have their own distinct characteristics and applications of the skill that simply 'work best' for them. By following this information, a forceful drop-punt kick can achieve its intended maximum distance. When coaches have a great understanding of biomechanic principles to increase skill efficiency, they create an advantage over opposing coaches who lack the knowledge, and can use cues in their coaching to achieve the optimal mechanical techniques to benefit their players (Sports Training Advisor, 2016).
The answer!
In order to perform a drop-punt kick optimally for distance biomechanics principles must be applied. To reinforce the information learnt, we will recap the essential noteworthy elements covered in how to achieve a drop-punt for maximum distance.
Phase 1: Approach- Requires the player to maintain an upright trunk position whilst slightly leaning forward, allowing balance and momentum transfer to occur. This phase also requires an increased delivery stride.
Phase 2: Supporting leg- Demands the player to manipulate their centre of mass from the center of their body over to the non-kicking leg. This helps increase balance and range of motion, as the non-kicking leg acts as a pivot point for the kicking leg to swing back further and increase force.
Phase 3: Ball drop- Demonstrates that the ball must be dropped at hip height with the dominant hand guiding the ball to the foot. Contact on the bottom third of the ball is key for the ball to spin backwards caused by the Magnus effect.Eye contact is also an essential element and must be kept throughout the kick for maximal accuracy.
Phase 4: Leg wind up and foot speed- Requires a high increase in foot speed and angular velocity to generate force. The flexion at the knee is an essential component for force and velocity output as it increase the stored elastic potential energy.
Phase 5: Contact and follow through- Involves the player to follow through with their leg by increasing hip extension and range of motion. The kinetic chain changes from a throw-like movement pattern to a push-like movement pattern. The body is propelled forwards from phase 5 and momentum is transferred from the body into the ball to increase overall kicking distance.
By using these biomechanics principles, an Australian rules footballer at any level whether they are elite athletes or grassroot beginners, they will be able to increase the distance and kick an effective drop punt which they can use to either maintain possession, kick to space or even kick a long goal, which will benefit their own performance as well as the teams performance by increasing their skill efficiency on the ground.
Phase 2: Supporting leg- Demands the player to manipulate their centre of mass from the center of their body over to the non-kicking leg. This helps increase balance and range of motion, as the non-kicking leg acts as a pivot point for the kicking leg to swing back further and increase force.
Phase 3: Ball drop- Demonstrates that the ball must be dropped at hip height with the dominant hand guiding the ball to the foot. Contact on the bottom third of the ball is key for the ball to spin backwards caused by the Magnus effect.Eye contact is also an essential element and must be kept throughout the kick for maximal accuracy.
Phase 4: Leg wind up and foot speed- Requires a high increase in foot speed and angular velocity to generate force. The flexion at the knee is an essential component for force and velocity output as it increase the stored elastic potential energy.
Phase 5: Contact and follow through- Involves the player to follow through with their leg by increasing hip extension and range of motion. The kinetic chain changes from a throw-like movement pattern to a push-like movement pattern. The body is propelled forwards from phase 5 and momentum is transferred from the body into the ball to increase overall kicking distance.
By using these biomechanics principles, an Australian rules footballer at any level whether they are elite athletes or grassroot beginners, they will be able to increase the distance and kick an effective drop punt which they can use to either maintain possession, kick to space or even kick a long goal, which will benefit their own performance as well as the teams performance by increasing their skill efficiency on the ground.
Additional resources
http://www.aflcommunityclub.com.au/
AUSKICK- Resources for coaches, parents and players. Providing lesson plans, tips and skill resources.
References
Ball, K. (2008). Biomechanical considerations of distance kicking in Australian Rules football. Sports Biomech, 7(1), 10-23.
Ball, K. (2011). Kinematic comparison of the preferred and non-preferred foot punt kick. Journal of Sports Science, 29(14), 1545-1552.
Blazevic, A. (2007). Sports Biomechanics: The basics: optimising human performance. A&C Black.
Blazevich, A. J. (2013). Sports biomechanics: the basics: optimising human performance. A&C Black.
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.
Dooghin, A. V., Kundikova, N. D., Liberman, V. S., & Zel’dovich, B. Y. (1992). Optical magnus effect. Physical Review A, 45(11), 8204.
Enoka, R. M. (2002). Neuromechanical Basis of Kinesiology. (3rd Ed). Human Kinetics, Champaign, IL.
Enoka, R. M. (2002). Neuromechanical Basis of Kinesiology. (3rd Ed). Human Kinetics, Champaign, IL.
Making Stridz, Athlete development. (2016). Developing better athletes one stride at a time. Retrieved by http://www.makingstridz.com/node/16
Millar, J. S. (2004). Kinematics of drop punt kicking in Australian rules football-comparison of skilled and less skilled kicking (Doctoral dissertation, Victoria University).
Orchard, J., Walt, S.,, McIntosh, A., & Garlick, D. (2002). Muscle activity during the drop punt kick. Science and football IV, 32-43.
Sports Training Advisor. (2016). Sports Biomechanics: The Rules of Sport Technique. Retrieved by http://www.sports-training-adviser.com/sportbiomechanics.html
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