THE DO OF PHYSICS
by Walter Gleason
This is the fourth of a series of articles on the use of physics in
Taekwon-Do. This issue of The Do of Physics examines in
depth the default foot formation commonly known as the
"sidekick" foot formation. In this examination we will rely on
anatomy, physiology, and biomechanics to describe and detail
the structure and working of the foot. In order to effectively use
the language of these disciplines, the appropriate terms and their
definitions are listed below:
3rd Class Lever
Third class levers produce speed and range of motion. This
is the most common lever type used by the muscular system.
A great deal of force is required to move a small resistance.
Ligament - Fibrous tissue binding bones together or lashing
tendons or muscles in place
Muscle - Contractile organ capable of producing movement
Origin - Relatively fixed point of a muscle attachment
Plantar - Refers to sole of foot
Plantar flexion - Movement of the sole downward toward the
floor
Proximal - Nearer to root of limb
Tendon - Fibrous tissue securing a muscle to its attachment
Toe extension - Movement of the toes upward
Toe Ffexion - Movement of the toes toward the floor
TERMS
Adduction - Movement toward axis of the trunk, as in lowering
the arms to the side
Distal - Further from root of limb
Dorsal - Refers to back; also back of hand and top of foot
Dorsal flexion - Movement of the top of the foot toward the
anterior tibia bone
Eversion - Turning the sole outward
Extension - Straightening; moving the bones apart, as when the
hand moves away from the shoulder
Fascia - Fibrous envelopment of muscular structures
Flexion - Bending; decreasing the angle between the bones
forming the joint as in the elbow joint when drawing the
hand toward the shoulder
Inversion - Turning the sole inward.
Lever system - A mechanism for doing work, consisting of a
body with an axis of rotation and eccentrically applied
forces. Lever systems and leverlike arrangements:
ANATOMY AND PHYSIOLOGY
Bones
1st Class Lever
This lever is useful for balance movements when the
fulcrum or balance point is midway between the applied
muscular force and the resistance. It produces speed and
range of motion when the fulcrum is close to the force, and
when the fulcrum is close to the resistance, it provides
greater force.
There are 204 bones in the human body. Each hand and wrist
and each foot and ankle has 26. This comprises over half the
bones in our bodies, and indicates how flexible, complex, and
important these extremities are.
• The ankle consists of 7 bones: medial, lateral, and
intermediate cuneiforms; navicular; cuboid; talus; and
calcaneous. These bones have a limited gliding movement,
and serve to absorb shock.
• The toes and foot consist of the 1st through the 5th
metatarsals; 5 proximal phalanges; 4 middle phalanges; and
5 distal phalanges.
The 26 bones of the feet are shaped in the form of arches
(longitudinal and tarnsverse) and are connected to the tibia and
fibula bones in the lower leg. The transfer of body weight is
from the tibia to the talus and calcaneus.
2nd Class Lever
The positioning of the resistance between the fulcrum and
the applied muscular force permits a smaller muscular force
to move a greater resistance. In the example above, the
articulation of the tibia with the foot is the resistance, and
the pull of the plantar flexors on the calcaneous at the back
of the heel is the force causing plantar flexion of the foot.
The fulcrum is the point where the foot contacts the ground.
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Articulations
Functionally, there are three major categories for the unions of
bones:
1. Immovable joints – Unions which are locked and allow no
movement. Sutures and cartilage are two types of these
joints.
2. Slightly movable joints – These are spongy cushions
between bones and are referred to as fibro-cartilage joints.
The discs separating and cushioning the vertebrae are an
example of this category.
3. Freely moveable joints – These are synovial or lubricated
articulations. The classifications are listed below:
• Plane – Bones glide face to face, limited by their
retaining ligaments. Examples are the bones of the
wrist and ankle.
• Hinge – Movement about a transverse axis only. The
elbow and knee are examples of hinge joints.
• Saddle – Like the hinge joint but with an additional axis
of motion perpendicular to the transverse axis.
• Condyloid – Like the saddle joint but with an additional
range of motion with a circular movement describing a
cone.
• Pivot – A cyliondrical form moving within a complete
or partial ring, or such a ring moving about the cylinder.
Only a vertical axis is present, as in the hinge of a gate.
The joints of the forearm bones are examples.
• Ball-and-socket – This joint is a spherical head set
within a cuplike cavity. Examples are the hip and
shoulder joints.
• Ellipsoid – This is a modified ball-and-socket. The
mating surfaces are ellipsoidal rather than spherical.
Vertical rotation is impossible. The wrist to forearm
(radio-carpal) joint is of this type.
•
and distal phalanges of the four outer toes and is a third
class lever in dorsal flexion.
Extensor hallucis longus - responsible for dorsal flexion and
toe extension. It is attached to the top of the distal phalanx
of the big toe and is a third class lever.
DESCRIPTION & PURPOSE
Over the millennia our feet have evolved and adapted for use in
upright locomotion over varied terrain, climbing, jumping, and
striking. These uses may be categorized as propulsive and
supportive functions, and are the adaptations which give us the
necessary flexibility, shock absorption, muscle tonus, and
biomechanical structure to form an effective striking tool.
When we practice kicking
techniques in the air in
class, we adopt the
"sidekick" foot formation
for turning kicks, rising
kicks, 45 ° kicks, reverse
turning kicks, etc. We do
this for two reasons: to
prevent injuries (a loose,
floppy foot can cause
hyperextension and trauma
to muscles, joints, and
ligaments) and to practice
proper foot formation and
kicking technique. It is difficult to determine whether the
illustration is of a sidekick, reverse sidekick, turning kick, or
reverse turning kick. This is because the foot formation and
alignment of shoulder, hip, and heel is identical at the
completion of each properly performed technique.
The sidekick foot formation is formed by four distinct actions:
Ligaments
The ligaments of the foot have the function of maintaining the
position of the longitudinal and transverse arches. The
longitudinal arch can be described as short and long arches. The
long arch runs along the inner side of the foot and is connected to
the calcaneus, talus, navicular, cuneiforms, and the three inner
metatarsals. The short arch is on the outer portion of the foot
and extends from the calcaneus to the cuboid and the fourth and
fifth metatarsals. The transverse arch spans the width of the foot
connecting the metatarsals.
Muscles
The muscles controlling the movement of the foot are located in
either the lower leg or in the foot itself. The muscles in the foot
are referred to as intrinsic muscles. These many small muscles
serve to support the arch of the foot and perform small balance
movements.
The muscles of greater interest to us are the muscles of the lower
leg which control the movements necessary for sidekick foot
formation. Those muscles are:
• Tibialis anterior muscle - responsible for dorsal flexion,
adduction, and inversion. It is attached to the medial
cuneiform and the first metatarsal bones and acts as a third
class lever.
• Extensor digitorum - responsible for dorsal flexion,
eversion, and toe extension. It is attached the tops of middle
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1.
Pulling the toes
upward and back
(toe extension).
2.
Pulling back on the
top of the striking
foot (dorsal
flexion).
3.
Twisting the foot so
the toes turned toward the inner ankle (adduction).
4.
the alignment of the kick is incorrect and the body is jackknifed
with the butt sticking out.
The side view below illustrates rigid orientation (locked joints)
of the long bones in the direction of the reaction force. Note that
at impact the body is leaning into the kick. The supporting leg is
angled toward the target; this puts the body's center of mass into
the kick and resists the reaction force. Of course, after the kick
the foot is immediately retratcted, returning the center of mass to
a stable position.
Turning the sole
inward so that outer
edge of the sole is
toward the target.
The stiking surface
is the heelward
portion of the outer
edge of the sole.
POWER AND THE SIDEKICK FOOT FORMATION
Taekwon-Do kicks are famous for being able to deliver
maximum power. In order to deliver a kick using the sidekick
foot formation with maximum power, the following elements
must be present:
1.
2.
3.
4.
The body and the foot must be in proper alignment with the
target.
• Shoulder, hip, and heel are in line.
• The reaction force from the impact needs to be
channeled down the length of the bones through
rigid joints down into the floor through the
supporting foot.
• At impact, all the body's weight is focused onto the
surface of the striking tool meeting the target at
impact.
The foot must have the proper orientation toward the target.
This is illustrated in the description of foot formation in the
preceding section.
• The proper portion of the foot must deliver the
blow. This is the outer edge of the heel.
• The force of the kick must be focused on the
smallest possible area on the tool.
The foot must go directly to the target (not a glancing blow).
The foot must be rigid when the target is struck.
ELEMENT 2
Inherent in all striking tools is a degree of shock absorption or
cushioning. In the foot there is extensive aponeurosis
(connective tissue for the bundles of ligamentous tissue) and
fatty material. They cushion and protect the foot during
movement. The layers of callus built up on the sole of the foot
also cushion and protect the foot from the reaction forces of the
foot striking the ground. None of these tissues are the focus of
our discussion of shock absorption.
Figures 1a and 1b above
illustrate the result of
striking with the ball of
the foot in a sidekick.
Figyre 2 illustrates a
heel strike. The large
calf muscles, ligaments, and tendons at the back of the calf act as
shock absorbers when we strike with the ball. The energy lost to
the shocks is energy subtracted from the impact. When the
reaction force is channeled into the ankle and down the long
bones of the legs, this is analagous to striking by jabbing with the
end of a broom.
In the following discusson we will focus on these elements and
use the side kick as an example of a kick using this foot
formation.
ELEMENT 1
When striking an object (assumed stationary) with the foot we
experience a reaction force at the point of impact equal and
By orienting the edge
of the heel toward the
target we accomplish
two things: we reduce
the surface area of the
striking tool and we
direct the reaction force down a rigid path. Also, the edge of the
heel presents a smaller surface area than the flat of the foot.
Applying the same force over a smaller area results in a greater
concentration of force focused on the target.
opposite to the striking force.
The above top view of a sidekicker and his skeleton illustrates
the way the heel (the striking surface), hip, and shoulder line up.
The resultant reaction force of the kick (shown by the black
arrows) is directed down the length of the long bones of the
upper (femur) and lower leg (tibia and fibula) into the hip and
down into the ground through the long bones of the supporting
leg. Note that the kicker is looking at the target over his
shoulder to maintain his line. This provides a view of the back
of the knee. If you cannot see the back of the knee, chances are
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ELEMENT 3
Force is a vector. It has both
magnitude and direction. If
the sidekick foot swipes the
target with a glancing blow,
some of the energy of the
blow is lost. The vector of
force has two components.
One is perpendicular to the target, and one is tangential to the
target. The greater the tangential component (the more the kick
swipes or glances), the lesser the perpendicular component.
Obviously a kick with a tangential component of zero would
have a perpendicular component equal to a kick driven directly
into the target.
ELEMENT 4
It is imperative that the sidekick foot formation be held tightly
before and during impact. The foot is held taut and rigid to
prevent injury and reduce the loss of energy due to shock
absorption. It is important to note, however, that the body itself
is relaxed prior to impact. Otherwise, opposing muscles in the
leg would reduce the speed of delivery.
OBSERVATIONS
A good sidekick is like a
good hammer blow driving
a nail into a board. When
the hammer meets the nail
squarely on the head, the
nail pierces and penetrates
the board. When the nail
is struck with a glancing
blow, the nail is bent and
penetration is minimal. If
one tried to drive the broad
surface of the nail head into the board, the board would only be
dimpled.
Although at first glance it may appear that there is an
overabundance of detail in this article (certainly more than
necessary for the simple act of forming a simple sidekick foot
formation), the author is convinced that the greater the depth of
understanding one has on a topic, the greater the ease of
application. The wealth of detail presented here should serve as
reference material and a basis for thought and discussion.
NEXT ISSUE
In the next issue we will continue investigating the formation of
Taekwon-Do tools by focusing on proper sudo or knife-hand
formation.
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