Below is our article on the mechanics of kicking in football. A great piece published on 7m, it demonstrates the importance of technique, without which injuries occur. At Response Physiotherapy, we'll analyse your technique as part of treatment and rehabilitation, to find out where it went wrong, and return you back to full sport.
Biomechanics of kicking in football
Sports all across the World make use of the complex action of kicking to thrill and entertain us. In terms of kicking sports, football is the most popular with over 250 million players across the globe. A game of football is determined essentially by who has been the most effective team throughout the game with their kicking. Although there are many essential factors which determine a successful football player, kicking ability is arguably the most important. You can always try to estimate it by yourself watching a game at the stadium, all you need to do is to buy the tickets beforehand (go to https://ticket4football.com/premiership-football-tickets/manchester-united-tickets).
Successful kicking mechanics could be defined as a mechanically efficient movement pattern that is repeatable, consistent and accurate in its outcome. The kicking action can be split up into six stages:
The angle of approach before striking the ball is the first stage. If you observe a toddler striking a ball, you will see that they run straight on and kick the ball head on. As they get older they realise approaching the ball with a paced run up and at an angle provides a better strike. Research has shown that striking the ball at approximately a 45 degree angle is optimal. This is because an increased angled approached allows the hip of the striking leg to rotate more, causing a larger striking surface area of the foot, and therefore a faster ball speed and/or improved accuracy. However, increasing the angle of approach too much can compromise and injure the knee and hip due to the increased tension from the rotational forces.
Following the approach, the next stage is to plant the supporting foot next to the ball. The position of the plant foot in relation to the ball will determine the direction and trajectory of the kick. Too wide, the pass will be sliced. Too close, the ball will be hooked. And too far forwards or backwards, in relation to the ball, will decrease or increase the flight path of the ball respectively.
Another necessity here is to have sufficient leg strength to hold and balance on one leg whilst simultaneously striking through with the opposite leg. If the kicker is right footed, the weight has to be transitioned to the left leg to allow for “space” to swing the kicking leg through. See the picture of David Beckham below.
Technique such as this takes tremendous strength and stability from the left hip; in particular, the gluteal muscles and some of the smaller muscles that surround the hip joint to provide stability i.e. deep lateral hip rotators. The trunk muscles, which are often referred to as the “core” muscles, have to also work extremely hard to counteract the speed and forces of the body and to allow for a stable base for the hip to move powerfully from. The muscles on the side of the body, which consist of the inner and outer oblique’s and quadratus lumborum, contract hard to resist the rotational forces of the trunk in relation to the lower limbs. As shown in the picture, the supporting leg has to flex to allow for the opposite foot to strike the ball. This is achieved through the co-contraction of the quadriceps and hamstring muscles of the thigh.
The third stage of kicking mechanics is called swing limb loading – often referred to as “swinging” or “cocking” the leg back. This is where the energy is generated for the kick. The movement initially begins through a contraction of the gluteus maximus and hamstring muscles, causing hip extension and knee flexion respectively. This is a concentric contraction where the muscles contract and shorten to bring the two joints together. To control this backwards motion of the leg, the hip flexors and quadriceps on the front of the thigh have to then contract to decelerate the movement. This is achieved through what is called an eccentric contraction. An eccentric contraction is where a muscle contracts whilst simultaneously lengthening to control the speed of the movement. In terms of striking a football, when the leg is cocked back, the hip flexors and quadriceps eccentrically contract to decelerate the leg. The energy through this eccentric contraction is then “held” in the muscle, before being released in a forceful concentric contraction in the opposite direction. This is what causes the power of the kick.
The fourth stage is the transition between the controlled backwards deceleration of the swing leg into a rapid acceleration in the opposite direction. This is termed as hip flexion and knee extension of the swing leg. The hip flexors, comprised of primarily the iliacus and psoas muscle, and the quadriceps muscles use the elastic energy which was stored during the swinging back phase to “whip” the leg forwards. The hip flexes first which takes the knee from behind the ball to directly over the ball. The quadriceps contract to then strike the knee into extension which causes the ball to be propelled forwards at speed.
This takes us to the fifth stage of kicking mechanics: foot contact. This stage of kicking is essential to the success of the kick. Firstly, to get into the correct position to allow optimal contact and trajectory with the ball, the hip of the kicking leg is externally rotated. As the ball is struck, the ankle must be fully flexed down. This is called plantarflexion – or in football lingo, “locking” the ankle. This is essential as without full plantarflexion of the ankle not only is power and speed reduced as the forces are not efficiently transferred into the ball, the risk of ankle injuries and the need to wear an amazon ankle brace increase due to the instability of having a joint which isn’t locked into position. At the point of impact, approximately 15% of the kinetic energy of the swinging limb is transferred into the ball. The majority of the energy is dissipated by the eccentric activity of the hamstrings to slow the leg down. This is the stage in the kicking action which is most likely to produce injury to the hamstrings due to the large forces involved.
The follow through is the final aspect of kicking mechanics. It is important for two reasons: (1) to maintain foot contact with the football for a longer duration, and (2) to reduce the risk of injury. A longer foot contact time is important for power and speed of the pass or shot. This is correlated to the formula “force = mass x acceleration”. The longer the contact time with the ball, in combination with fast acceleration, will generate in the highest amount of force, therefore resulting in a powerful pass or shot. In terms of the second point, the follow through is important to reduce the risk of injury as the body needs to dissipate the kinetic and elastic forces produced from kicking action. If a sudden stop of the kicking leg occurred, muscles such as the hamstrings could be damaged and strained as the large forces involved would need to be stopped abruptly.
Tom Hames, Chartered PhysiotherapistReferences
Barfield, B (1998), The biomechanics of kicking in soccer. Clinics in Sports Medicine. 17(4): 711-728
Brukner, P, and Khan, K (2012), Clinical Sports Medicine(3rd ed). Roseville: McGraw-Hill.
Gainor, B, Pitrowski, G, and Puhl, J (1978), The kick. Biomechanics and collision injury. Am J Sports Med.6:185-193.
Isokawa, M, and Lees, A (1988), A biomechanical analysis of the in-step kick motion in soccer. In Reilly, T, and Williams, M, (2003), Science and Soccer (2nd ed). Routledge: London. pp. 449-455.
Kellis, E. and Katis, A. (2007), Biomechanical characteristics and determinants of instep soccer kick. J Sports Sci Med. June; 6 (2): 154-165
Lees, A., Asai T., Andersen, T., Nunome., H and Sterzing, T. (2010) The biomechanics of kicking in soccer: a review. J Sports Sci. Jun; 28 (8): 805-817