Download Biomechanics of kicking in football Sports all across the World make

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.
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:
1. Approach
4. Hip flexion and knee extension
2. Plant foot forces
5. Foot contact
3. Swing limb loading
6. Follow-through
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.
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 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, Physiotherapist
References
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