What are the biomechanical aspects of a soccer penalty kick (on goal) help to enhance and improve the shot?

What are the biomechanical aspects of a soccer penalty kick (on goal) help to enhance and improve the shot?

Biomechanics are often used to define and improve aspects of soccer games. Biomechanics helps to break down particular skills or movements to help the player and coach to further understand the movements. Once a better understanding is developed, this then helps the player to be able to change their movements in order to better improve their play. This blog will focus on the biomechanical aspects of a soccer penalty kick. Areas that will be outlined are the importance of the run up and biomechanical aspects within the run up, the strike or kick of the ball and the follow through of the kick.

The soccer penalty kick is used in a couple of different scenarios during a game of soccer. The first penalty kick used in a match, is when a foul is awarded against the opposing team, allowing the non-offending team to take a free shot on goals with the only defence being the goal keeper.  The second time an on goal soccer penalty kick are used, is if the team is playing in a cup round or final where the score is a draw at full time. The penalties are used after two short halves of extra time if the score is still a draw. Each team gets five shots on goal to try and reach a final score. This type of penalty decides the outcome of the match. The other type of penalty kick is performed from outside of the goal square and the defending team use a wall of players which makes the kick harder for the non-offending player to score a goal. The aim of every penalty kick is to get the ball past the goal keeper to score a goal. The kicker can achieve this by using maximum acceleration, power and swing on the ball to make it harder for the goal keeper to read the play.

 (Retrieved: www.soccer-universe.com)

How does the run up in the soccer penalty affect the accuracy of the kick?
Newtons Law
The accuracy of the kick is primarily determined by the angle of release, velocity, newton’s law and body positioning. A study done in 2008-2009, looked at the effects of altering the approach angle in the soccer penalty kick performed by recreational soccer players (Scurr, Hall, 2009). The study showed that altering the angle did not change the accuracy or velocity of the ball (Scurr, Hall, 2009). Although the alteration of angles did not change accuracy or velocity of the ball, the study found that by widening the approach angle, the player formed a larger hip rotation creating a bigger movement before and during contact with the ball (Scurr, Hall, 2009). 

At the beginning of the run up, the player must accelerate to overcome their own inertia to produce enough momentum and force to get behind the ball so that the ball can make the full distance to the goals, which is commonly 11/12 metres away.  Ideally, the player must aim for the greatest velocity forced upon the ball as this creates a smaller amount of time for the goal keeper to make a decision, making a more likely chance of the player scoring a goal. The moment of inertia needs to be overcome for not only the player, but also the ball. This is Newton’s First Law, which states that: ‘An object will remain at rest or continue to move with constant velocity as long as the net force equals zero’ (Blazevich, 2010). This explains what happens once the player has started running; the ball has been kicked and is now in motion towards to goals and goal keeper. 

Newtons Second Law states that: ‘the acceleration of an object is proportional to the net force acting on it and inversely proportional to the mass of the object’ (Blazevich, 2010). As stated before, the more force applied to the ball, the more acceleration moves through therefore reducing the goal keepers reaction time making a higher chance of scoring. 

Kinetic Chain
In order for the body to be able to move successfully, joints and movements must work together sequentially. This is called the Kinetic chain and is broken up into two patterns which are considered to be; the push like pattern and the throw like pattern (Blazevich, 2008).

The push like pattern is performed as it sounds; the pattern is executed as if the body is pushing something and uses all joints instantaneously (Blazevich, 2010). The throw like pattern is different to the push like pattern, as instead of the joints moving altogether, they now move one by one, after each other (Blazevich, 2010).

The soccer penalty kick uses a throw like pattern as the body moves sequentially through the movements from the joints. The skill movement starts as a run up, involving the extension and flexion of the hips and knees, the shoulder retracts backwards and the feet moving between plantar flexion and dorsiflexion as they player runs. As the player lands their non-preferred foot next to the ball, their hips rotate forward, followed by the knee flexing and finally their foot receiving contact with the ball for the kick. Through this motion, the player summates force through the ball that has been generated through the run up and the sequential movement of the hips, leg and feet.

Shown below is a picture of a soccer player moving through the stages of the kinetic chain throw like movement.

Figure 1: Kinetic Chain of Soccer Penalty Side View
(Retrieved: http://folioz.ca/artefact/file/download.php?file=24233&view=3153)

Figure 2: Kinetic Chain of Soccer Penalty Frontal View
(Retrieved: http://folioz.ca/artefact/file/download.php?file=24233&view=3153 )

The Magnus Effect
The Magnus effect explains the motion of the swing or curve that a ball makes during motion. The Magnus effect occurs when the angular acceleration on the front of the ball is greater than the angular acceleration on the back of the ball, therefore causing the ball to curve through its motion (Blazevich, 2010).  As the ball is projected through the air, the friction of the air helps the ball to catch and slow down. The ball is slowed on one side as the friction occurs, whilst the opposite side continues to glide through, developing the curve in the balls direction later in the flight (Blazevich, 2010). 

 Figure 3: The Magnus Effect
(Retrieved : http://www.mecaro.jp/eng/images/introduction_i06.gif)

In the soccer penalty kick, the kicker’s main aim is to score the goal by getting the goal past the goal keeper. The Magnus effect can greatly benefit the kicker in this aspect, as creating a swing on the ball can confuse the goal keeper and lead to scoring the goal. Although the player must be able to get the correct spin on the ball so it doesn’t lift and spin over the goals or drop too short. Therefore the player must aim to create as much swing on the ball as possible, making it harder for the goal keeper to read where the ball is going to end up. Soccer plays tend to put spin on the ball so that they can curve the ball around a wall of defenders or around the goal keeper. 

Torque
Torque is a moment of force that forces the object to rotate around an axis. During a soccer penalty kick, the player uses torque to help rotate the hips and torso through the ball (Bauer et al, unknown). This enhances the velocity of the kick and therefore also helping add to the Magnus effect and performing a successful curve in the penalty shot. Torque also helps the player to overcome the moment of inertia in themselves and on the ball as it helps to gain momentum into the motion (Bauer et al, unknown; Blazevich, 2010).

Stability

During the preparation phase of the soccer penalty kick, the body goes through a sequential throw like pattern to perform the action. It is essential to maintain stability; this can be done by the maintaining of the centre of masses and centre of gravity.  In a soccer penalty kick, this is done by distributing the player’s weight evenly on the balls of their feet during the run up (Bauer et al, unknown). When the player makes contact with the ball, the player slightly moves their torso backwards to account for the contact with the ball. A player also should use their arms to evenly distribute their mass evenly and ultimately staying balanced during the penalty (Bauer et al, unknown). The centre of mass and centre of gravity is a point in the body where all of the body is evenly distributed (Bauer et al, unknown). The more stable the player performing the shot is, the more smooth the shot will be whilst driving the leg through for the contact on the ball. To finish the kick, the follow through motion should be performed to maintain a smooth balanced kick. Without the follow through, balance may be lost which will affect the accuracy of the overall kick.

The Answer
There are multiple biomechanical aspects to the game of soccer, in particular the soccer penalty. It is evident that there are many different aspects that can affect the kick, positively and negatively. 

The biomechanical aspects of the soccer penalty kick can be broken down into smaller parts in order to achieve successful outcomes or enhance the overall quality of the shot. The different laws of biomechanics are very influential in supporting the accuracy, speed and velocity of the shot. 

There are many studies that have looked into the link between ground reactions forces and ball speed. Experiences and elite players produce higher greater reaction forces in all the different directions and generally kick faster and more accurately consistently (The Sports Injury Doctor, unknown). 

In order for a player to become more consistent with their soccer penalty kick, they need to fully understand the biomechanics of the skill. Once they have achieved this, they can understand why they are doing the particular activities and why the skill is so complex. The biomechanical aspects all add to enhancing the player’s penalty kick. The Kinetic Chain ‘throw like’ pattern moves through the joints as a sequence in order to successfully and smoothly perform this aspect of a soccer game. This allows the body to execute the particular movements to create optimum force and velocity to put behind the ball for the shot on goal (Blazevich, 2010).

The Newtons Law’s, play a massive part in the enhancing of a penalty kick. The law’s all effect the accuracy of the kick through angles of release, velocity and body positioning. Newton’s first law explains how the moments of inertia are overcome for the player and the ball which is the beginning of power into the soccer penalty kick. Newton’s Second Law shows the speed of the kick and having the same mass as the ball, therefore the speed of the ball is reliant on the force applied by the player.

These biomechanical aspects can all be enhanced through the breaking down of the skill and execution of the different laws in the area. There are constraints which can impact on the skill.  These are organismic, environmental and task constraints which give feedback and may affect the ability of the player to perform the skill. 

How else can we use this information?

In order to enhance the soccer penalty kick; coaches, teachers, players and student spend a lot of time breaking down the biomechanical aspects. These can easily be transferred into other sports that also follow the same kinetic chain- the throw like pattern. Other sports that follow the kinetic chain’s throw like pattern are: cricket, volleyball, basketball, tennis, Australian Rules football and many more. Although some of the aspects may need to be slightly altered to suit particular sport’s they can all be transferred between each other to successfully enhance athlete, players or students in several different sports.

References

Blazevich, A. J. (2010). Sports biomechanics: the basics: optimising human performance. A&C Black.
McLester, J. (2008). Biomechanics and Related Movement Disciplines. Applied Biomechanics: Concepts and Connections (pp. 8). Retrieved from http://books.google.com.au/books?id=JsFvOy1w-1QC&printsec=frontcover#v=onepage&q&f=false  

Quinn, E. (May 16, 2014). Proprioceptors - What Are the Proprioceptors and Proprioception. Retrieved 19/6/14, from http://sportsmedicine.about.com/od/glossary/g/Proprioceptors.htm

Scurr, J., & Hall, B. (2009). The effects of approach angle on penalty kicking accuracy and kick kinematics with recreational soccer players. Journal of sports science & medicine, 8(2), 230. http://www.jssm.org/vol8/n2/10/v8n2-10text.php

Pelz, E. (2014). Newton's Law. Retrieved 19/6/14, from http://prezi.com/axkwrzjngds4/newtons-laws/

Lee Bauer, Evan Fryer Christian Levesque, and Shannon O’Brien (unknown). Qualitative Biomechanical Analysis of a Penalty Kick in Soccer. Retrieved 15/6/14, from folioz.ca/artefact/file/download.php?file=24233&view=315

The Sports Injury Doctor (unknown). Biomechanics of Soccer: The soccer-style kick - a slow-motion commentary on one of the most common sporting actions in the world. Retrieved 15/6/14, from http://www.sportsinjurybulletin.com/archive/biomechanics-soccer.htm