The striking of an object with the foot is a uniquely specialised activity and needs specialised discussion, as the action it produces is the only common form of striking that does not directly involve motion from the arms. It is with this in mind that an understanding of the qualitative analysis, with a special interest of the open skill and a discrete motor sequence of kicking involved in the game of soccer. This discussion shall focus of such motion. In soccer the range shown to the various techniques used to strike a football are numerous with a vast amount of angles in which to strike the ball from whether it be a side pass to a instep drive , they can range from a low velocity pass to a fellow player standing a small distance away using the side of the foot, a concentrated effort required when a stationary football needs precise accuracy and a high velocity when taking a penalty kick to the maximal effect needed and the Optimal angles involved when lifting a football from the ground and over participants’ heads away from your own goal; it is the latter statement that this topic is based upon using the skills involved with the instep. Throughout this discussion it is up to the reader to take a holistic approach to the skill of kicking and continue the research needed for a complete picture to the skill of kicking.
The highest speeds involved with striking a football have been quoted to be in excess of 30 m/s, and it is where the contact is needed to be with the instep of the foot for these speeds to be reached. It has also been seen that there is a 4 fold increase from the velocity produced by the three dimension motion created at the hip (5 m/s) to the velocity that the ball leaves the toes, with the knee and ankle increasing their velocity to the transfer of kinetic energy needed at 7 m/s and 15 m/s respectably. This interesting sequences of events has been shown in the sequential motion associated with the hip, knee and ankle motion or otherwise known as the proximal-to-distal sequence ( this describes the way energy within the muscles is associated around the hip, knee and ankle to the speed the ball leaves the toe). Looking within the figures above, the football leaves the foot within 0.22≈ seconds after initial contact and the timing of sequences involved in the destitution of force effecting the kick is shown as, hip 0.1≈, knee 0.15≈ with the ankle and toe showing a minimal difference at around 2≈. With the above information it is apparent that the striking of a football is a finite interaction of neuromuscular control and any timing, difficulties within this timing and control can then have an impact on the quality of motion need in produce an optimal kicking sequence. The instep kick in football has shown to have some major phases of motion, the following is a short description of the phases involved with a more in-depth discussion consisting the remaining of this topic.
The mature form of the kicking skill has been characterized by an approach to the ball of one or more strides with the final stride being that of a jump, step or lung. The placement of the supporting foot is at the side, and slightly behind the stationary ball. The kicking leg is first taken backwards and the leg flexes at the knee (called leg cocking). The motion of the swing leg initiates a action-reaction of the opposite arm (Newton’s third law of motion: If a body exerts a force on another, there is an equal and opposite force, called a reaction on the first body by the second) Forward motion is initiated by rotating the pelvis around the vertical axis (the supporting leg) and by bringing the thigh of the kicking leg forwards while the knee continues to extend. Once this initial action has taken place, the thigh begins to decelerate until it is essentially motionless at ball contact and the action-reaction causes the opposite arm to the kicking leg to reverse their rotations around its vertical axis. During this deceleration, the shank vigorously extends about the knee to almost full extension at ball contact the leg remains straight through ball contact and begins to extend during the long follow-through. The foot often reaches above the level of the hip during the follow-through.and a final jump or hop can be seen when conservation of momentum continues past its point of impact.
A characteristic of soccer kicking is the approach angle that the player takes to kick a stationary ball. Experiments have used various approach angles to established optimal alignment, these include angles where a participant was required to take a one-step run-up to kick a stationary ball using approach angles of 0, 15, 30, 45, 60 and 90° (the direction of the kick was 0°). As stated previously there is a 4 fold increases from the velocity of motion around the hip to the velocity produced by the toes at impact, this suggest that the motion of the shank (being involved with both the knee and ankle) in extension prior to impact influences the final speed in which the ball leaves the toe. The maximum velocity of the shank was achieved with an approach angle of 30° and the maximum ball speed with an approach angle of 45°.Therefore, an approach angle of 30 to 45° would appear an optimum angle for both velocity of the extension of the shank and maximal speed of the ball being reached at impacts. The explanation given for this is that an angled approach has three advantages, firstly the approach angle enables the leg to be tilted in the frontal plane towards the football with the standing leg being in slight flexion, without this lean the swing leg would not have enough clearance to make contact with the optimal angle of the ball as this swing leg needs to be in extension prior to impact for optimal alignment, without this lean the swing leg would make contact with the floor or a change in mechanics is needed for the swing leg to clear the ground resulting in instability of a stable base which is needed for the optimal kicking performance . The second advantage it provides is that the foot can if required, be placed further under the ball thus making a better contact and allowing for better control of the foot, the better control of the foot allows the foot to move across the ball, this gives a greater scope for the foot to apply spin to the football in any direction required. Finally during impact the swing leg will follow a path of a lateral to medial plane, this allows a transverse rotation of the pelvis (vertical axis) as well as the frontal devotion (ant-post axis) due to the lean into the ball, and the lean of the trunk (which will be explained later) enables the midsection (med-lat axis) to be loaded in a tri plane coupling (tri-plane axis, all axis and corresponding muscles are loaded-stretched ready to be unloaded-contract) which enables a greater action-reaction of the upper trunk ( Newton’s third law) to counter-react against the motion created by the pelvis resulting in the opposite arm and leg meeting on impact and a greater force production impacted on the ball.
The placement of the supporting foot has received little attention in soccer. The optimal foot plant position for accurate direction is perpendicular to a line drawn through the centre of the ball for a straight kick. The ideal medial- lateral position of the plant foot as 5 to 10 centimetres to the left of the ball (assuming a right-footed kick), it is explained that if the plant foot is greater than 10 centimetres away from the ball, the direction of the kick and the kicker’s balance can both be compromised. The ideal anterior-posterior position of the plant foot is when kicking is adjacent to and in line with the ball. The anterior-posterior position of the plant foot is what determines the trajectory or flight path of the kicked ball. Novices tend to plant their foot behind the ball, which produces a higher ball flight path, whereas a forward plant foot position results in a low trajectory Foot placements in elite junior soccer players of 38 cm behind the ball centre, and 37 cm to the side of the ball centre. From other codes of football, it has been reported that the supporting foot should be placed 5 to 10 cm to the side of the ball, but the anterior-posterior positioning is equivocal, and suggesting say a placement of 5 to 28 cm behind the ball It is likely that the anterior-posterior positioning is a function of the type of kick performed and whether it is intended to keep the trajectory of the ball low or to make it go high.
During the last few years it has been noted that individuals who are involved in a kicking sport have taken advice from rugby. The crosses over from kicking a rugby ball to a football are very closely, if not identical in their motor patterns except for a few small changes. In football an instep kick from a stationary ball like those motions of a place kick by goalkeeper seem to produce a lateral to medial motion around the vertical axis, this has a biomechanical advantage for the tri plane loading of the kinetic chain, but a down side is seen in many who’s motor pattern has not matured enough to optimise this motion. An individual seen above may during the course of a kick and especially when induced by mental and physical fatigue as well biomechanical changes, could have a tendency to slice or hook the ball very much like those of a golfer, this will certainly reduce the accuracy and direction of the kick. In rugby, the kick is all dependent on the very finite accuracy and direction needed to covert a kick, where even if the accuracy of a goal kicker is poor as long as the ball arrives in the area of the team players this seems to be enough. There is information which has been taken from rugby in attempting to produce more accuracy through the biomechanical pattern of the kick, when the goalkeeper strikes a football we see that there is a angle of approach (this as discussed is vital for many reasons), and when there is impact it is shown that the leg performs the lateral- medial pattern around the vertical axis, if this path is traced it can be seen to be that of a C shape motion (from the initial run up to the impact implanted on the ball). Where rugby differs, and has been quoted to be more accurate in there kicking is, when the leg performs its lateral motion and preparing for the action back into the medial plane the angle is smaller, and where in football the swing leg appears to end past midline (the line between the standing leg and the swing leg on impact) in rugby the swing leg only goes through little medial rotation and never crosses the mid line, if this path is to be traced it will form a J shape pattern. This difference in the kicking styles allows the foot to lead the knee, shank and hip in pointing to the direction the ball is intended to go and enables the kicker to minimise a slice or hook. This seems to be an obvious statement but more research is needed to whether the C or J shape is better for accuracy and direction of a ball, as changing the kicking pattern can change the mechanics of the kick from the initial run up to the impact on ball strike (it also is interesting to see that the kicker in rugby has a smaller run up and a slightly increased approach angle then a football kicker).
It is to be expected, up to a point, that a longer and faster approach would be a benefit in the generation of high ball speed, but due to the last stride being a jump, step or lung the speed on approach is influenced by the neuromuscular timing and sequencing of proximal-distal sequencing, the motor patens of repetition and the stride length, stride rate and cadence. Again there seems to be an understanding to the differences between a stationary and running approach when making a maximal instep kick. Maximum ball speeds of 23.5 m s- 1 when using a stationary approach and 30.8 m s- 1 when using a 5 to 8 Stride running approach. This approach suggest that the running approach has a greater influence not only on the momentum of conservation transferred through the kinetic chain but also in the maximal velocity required at impact through the toes to the ball, but a concern arises when excess speed compensates for a inadequate motor pattern. It is interesting to note how sprinters and long jumpers approach the acceleration phase of the sprint, as both of these sports will have to braking force applied to the ground either to stop or to apply force upon the ground and create an opposite reaction in directing them vertically and horizontal at take off.
During the start of a 100 meter event it’s recommended that the first stride is 50 cm in front of the front leg (by their rear leg), and is increased 10cm with each stride until full acceleration is achieved. This works out that there are 50 strides per 100 meters, 2 meters per stride, and leading up to 2.30 meters per stride which is the top stride rate. This stride rate occurs after 19 strides and approximately at 27 meters. it is after this 19 stride or 27 meter mark where the sprinters posture is vertical and in full stride, it has also been mentioned that these figures can increase to 15 cm after the first stride up to a maximum of 2.50 meters per stride, resulting in 14 strides in 22 meters, but these results seem to relay on the power, height of the individual and the length of the lower limbs. From these findings and using the equations stride length= height of individual and stride rate=length of lower limb² (² being the square of either the height or length), an optimal running stride, stride rate and cadence can be equated for each individual. Due to the sequence of the last stride, being a jump, step or lung there is adapted compensation effect carried out due to the high impact produced through the kinetic chain, and with an increase in speed preferred over a motor paten this will require a deceleration and braking effect applied to the foot and up the kinetic chain reducing momentum in both vertical (ground reaction forces, centre of gravity) and horizontal (frictional forces) planes and force production in both theses directions decreases. An understanding of the optimal stride length and stride rate using the equations above along with an increase in stride length shown in the 100 meter sprinter and optimal performance for each individual can be implemented.
The long jump is an event that requires an athlete to jump as far as possible from a fast run up into a pit of sand. The distance jumped is largely determined by the flight distance and this is determined by the height, speed, and angle of projection of the centre of mass at takeoff. The speed and angle of projection are determined by the combination of horizontal and vertical velocity. The horizontal velocity is developed through the approach run, which is usually of sufficient length for the athlete to be close to maximum speed at
The takeoff board.
The vertical velocity is generated during contact with the board. If we assume that the athlete is able to generate maximum speed close to the board, the problem of long jumping becomes one of generating vertical velocity from the board. This vertical and horizontal velocity needed for distance in a jump has a close correlation with our kicker. As our kicker approaches the ball the amount of vertical and horizontal distance to the football is reliant on the amount of vertical and horizontal motion created by the proximal to distal segments and ultimately to the whole body as seen when the final position of the body is forward and upward of impact. But as previous stated a jump, step or lung when in the last stride is a fine coordination of the motor pattern whether in a open or closed loop control and comes across some mechanical advantages which if conditioned allows for the conservation of momentum to continue into impact and not lost in kinetic energy to the ground (some is lost which enables for ground reaction force to be used in vertical and horizontal motion). When the final stride is approached and a jump, step or lung is taken, there is pivot mechanism seen in the long jump which may enhance kicking. The pivot mechanism explains three of the main observations of the touch-down in the long jump, which are that successful jumpers have (a) a high approach speed, (b) a low centre of mass at touch-down and (c) a leg at touch-down which is extended in front of the body. The low centre-of-mass position enables the touch-down leg to be flatter to the ground when contact is made and is seen on contact phase of the last stride, thus creating the conditions for the pivot, while the high approach speed ensures the pivot is functional allowing the body to rise over the standing leg and continue the momentum up and forward. Furthermore, the pivot mechanism also explains why the high approach velocity is related to distance jumped. It is the combination of high horizontal velocity (generated through the approach run) and high vertical velocity (generated by the pivot) that enables a greater distance to be jumped, which can relate to the final body position seen after the football is struck. Due to the vertical and horizontal motion of the legs, arms and torso (in it’s every changing centre of gravity) the velocity of the proximal to distal segments as well as the velocity of the ball is at maximum. It is important not only to look at football for inspiration but to activities that closely resemble the motion in which you are studying.
Before we leave this section of approach angles and speed an interesting sequence of motion that is too often neglected is the action of posture in motor patterns. During the action of the kick there is a sequence of proximal to distal timing of the transfer of kinetic energy seen from the hips to the toes, with times as short as 0.15 (15 ms) to 0.2 (20 ms) seconds but what about the motions of the arms. We have seen that as motion occurs at the hips there is a counter reaction created within the mid section to produce an equal but opposite reaction of the arms so we have controlateral motion, but before the shoulder muscles allow for the pendulum motion of the arms to make this reaction, some 80ms before the shoulder starts to move there is activation within the lower back and legs muscles enabling the oscillation of motion to be small. Along with this timing of the back and legs in making their adjustments, it has been seen that some 10 to20 ms before the action of the hip allows for proximal to distal motion to the toes to occur, the muscles around the lower back switch on for the adjustment needed to counter balance the postural oscillation as shown. This short but precise input regarding of timing throughout the kinetic chain, and especially in motion associated with the arms a and legs, should make coaches question their core training when dealing with complex motor patterns such as kicking.
