NORMAL GAIT
•
It is the series of rhythmical, alternating
movements of limb and trunk, which results in the forward progression of the
center of gravity.
•
The gait cycle is the period of time between any
two identical events in the walking cycle e.g.: Time from heel strike to the next ipsilateral
heel strike. The gait cycle is divided into two periods
•
Stance
Phase
o It
is the phase of gait cycle in which the foot is in contact with the ground and
is bearing the body weight.
o It
is 60% of the total gait cycle.
•
Swing
Phase
o it
is the phase of gait cycle in which the foot is not in contact with the ground
and is not bearing the body weight.
o It
is 40% of the total gait cycle.
•
Step
length
o It
is the linear distance in the plane of progression between corresponding
successive contact points of opposite feet.
•
Stride
length
o It
is the linear distance between the corresponding successive points of heel
contact of the same foot.
•
Single
support
o It
refers to the period when only one foot is in contact with floor.
•
Double
support (20% of gait cycle)
o It
occurs when both feet are in contact with floor.
o The
absence of period of double support
distinguishes running from walking.
•
Cadence
o It
is the number of steps taken per minute. It may vary from 70 in slow walking to
130 in fast walking,
o Adult
male covers 2.50 miles or 4 km in one hour.
Sub divisions of stance phase
•
Heel contact
o The
instant when the heel of the reference limb touches the floor.
•
Ball contact
o When
the bases of the metatarsals of the reference limb’s foot touches the floor
•
Foot flat
o The
initial contact of the forefoot with the floor.
•
Mid stance
o When
the greater trochanter is in vertical alignment with the vertical bisector of
foot.
•
Heel off
o When
the heel of the reference foot leaves the floor.
•
Toe off
o When
the toe of the reference foot leaves the floor.
OR
It can be divided into
•
Weight
acceptance phase
o begins
at heel contact and ends with foot flat position.
•
Mid
stance
o Begins
with foot flat and ends with heel off.
•
Push off
o Extends
from heel off to toe off.
•
Sub
divisions of swing phase:
It can be divided in to:
•
Acceleration:
It is characterized by the rapid
acceleration of the lower end of the limb shortly after the toe off.
•
Mid swing:
It is the interval when the
swinging limb over takes and moves ahead of the limb in stance face (contra
lateral limb).
•
Deceleration:
It is the interval when the
swinging limb approaches the end of interval and slows down for heel contact.
Path of center of
gravity:
The laws of mechanics make it clear that the
least amount of energy is required when a body moves along straight lines, with
center of gravity neither deviating neither up and down or side ways. Which is
not possible in human beings? So the body’s center of gravity deviates from
straight line but for the sake of energy conservation, deviation should be kept
to an optimal level. This is done by the muscles and ligaments of the
body.
Vertical
displacement:
In the normal walking pattern the center of
gravity goes trough a rhythmical ups and downs as it moves forward but it is
extremely smooth with no abrupt change in direction. The highest point is in the mid stance and the
lowest point is in double support. The average amount of vertical displacement
is 5cm or 2 inches.
Lateral
displacement:
As weight is transfers from one limb to the
other one the pelvis also shifts to the weight bearing side and with it COG
also shifts. The total amount of sideway movement of pelvis
is 5cm or 2 inches. The limit is achieved in the mid stance and the path
followed by the COG is extremely smooth.
Gait characteristics that
influence the path of COG:
The characteristics that influence the path of COG are:
•
Flexion
on knee during stance
Just after the heel contact,
flexion of knee begins and continues until it reaches 20*. This characteristic
of normal gait helps to smoothen the path of COG and limits it’s up and down
osilation to an optimal level
•
Pelvic
depth
In normal walking the pelvis
drops on the swing side, i.e: stance hip adducts slightly. The amount of
displacement of the pelvis from the horizontal is controlled with in 5* by the
abductors of the hip of the contralateral side. In standing this dip found is
the positive trendelenberg sign, in walking it is normal and serves to reduce
the upward displacement of COG.
•
Pelvic
rotation
In addition to the dipping the
pelvic rotates forward in the horizontal plane. This rotation is 4* on each
side of the COG. This helps to reduce the vertical displacement of COG.
•
Width of
the walking base
In figure WB is the width of the
walking base that falls within the range of 5-10cm or 2-4 inches. As the pelvic
shifts towards the supporting side to maintain the stability so the normal
narrow walking base minimizes the lateral shifting of the COG.
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