Gait
Gait is the medical term to describe human locomotion, or the way that
we walk. Interestingly, every individual has a unique gait pattern.
A person’s gait can be greatly affected by injury or disease process. By
evaluating the gait pattern of an individual, a therapist can determine
specific weaknesses and adjust rehabilitation programs to address these
issues.
Normal Gait
Definition:
Physiological Definition:
It is a mechanism which depends upon closely integrated action of the
subjects, bones, muscles and nervous system (including peripheral and
central nervous system)
The degree of integration determines the different gait patterns. Any
defect of any part of them or all of them will lead to pathological gait.
Mechanical definition;
It is a form of bipedal locomotion as there is an alternating action
between lower extremities. One leg is in touch with the ground for
restraining, supporting and propulsion.
The other leg is in swing phase for creating a new step forward. So
gait is the result of a series of rhythmic alternating movement of arms,
legs, and trunk which create forward movement of the body.
Prerequisites of gait:
1. The ability to support or assume upright position.
2. The ability to maintain balance in an upright position during static
and dynamic situation.
3. The ability to develop or create new step forward.
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Forces for gait:
1. Muscular force.
2. Gravitational force.
3. Forces of momentum.
4. Floor reaction force.
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Gait cycle.
The gait cycle is used to describe the complex activity of walking, or our
gait pattern. This cycle describes the motions from initial placement of
the supporting heel on the ground to when the same heel contacts the
ground for a second time.
Phases of Gait
Each gait cycle can be described in the phasic terms of
Stance Phase:
Is defined as the interval in which the foot is on the ground (60% of the
gait cycle). Stance Phase is divided into:
1) Heel strike to foot flat
2) Foot flat through mid-stance
3) Mid-stance through Heel off
4) Heel off to Toe off
The stance period consists of the first five phases: initial contact,
loading response, mid-stance, terminal stance and pre-swing
a) Initial Contact
Initial contact is an instantaneous point in time only and occurs the instant
the foot of the leading lower limb touches the ground. Most of the motor
function that occurs during initial contact is in preparation for the loading
response phase that will follow.
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Initial contact represents the beginning of the stance phase. Heel strike
and heel contact serve as poor descriptors of this period since there are
many circumstances when initial contact is not made with the heel alone.
The term "foot strike" sometimes is used as an alternative descriptor.
b) Loading Response
The loading response phase occupies about 10 percent of the gait cycle
and constitutes the period of initial double-limb support. During loading
response, the foot comes in full contact with the floor, and body weight is
fully transferred onto the stance limb.
The initial double-support stance period occasionally is referred to as
initial stance. The term foot flat (FF) is the point in time when the foot
becomes plantar grade. The loading response period probably is best
described by the typical quantified values of the vertical force curve. The
ascending initial peak of the vertical force graph reveals the period of
loading response (see Figure 4) .
c) Mid-stance
Mid-stance represents the first half of single support, which occurs from
the 10- to 30-percent periods of the gait cycle. It begins when the contralateral foot leaves the ground and continues as the body weight travels
along the length of the foot until it is aligned over the forefoot. The
descending initial peak of the vertical force graph reveals the period of
mid-stance
d)Terminal Stance
Terminal stance constitutes the second half of single-limb support. It
begins with heel rise and ends when the contra-lateral foot contacts the
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ground. Terminal stance occurs from the 30- to 50- percent periods of the
gait cycle. During this phase, body weight moves ahead of the forefoot.
The term heel off (HO) is a descriptor useful in observational analysis
and is the point during the stance phase when the heel leaves the ground.
The ascending second peak of the vertical force graph demonstrates the
period of terminal stance .
Roll off describes the period of late stance (from the 40- to 50- percent
periods of the gait cycle) when there is an ankle plantar-flexor moment
and simultaneous power generation of the triceps surae to initiate
advancement of the tibia over the fulcrum of the metatarsal heads in
preparation for the next phase.
2) Swing Phase:
is defined as the interval in which the foot is not in contact with the
ground (40% of the gait cycle).denotes the time when the foot is in the
air, constituting the remaining 38 percent of the gait cycle.
the swing phase could be defined as the phase when all portions of the
foot are in forward motion.
Swing is divided into two phases:
1) Acceleration to mid-swing
2) Mid-swing to deceleration
The swing period primarily is divided into three phases: initial swing,
mid-swing and terminal swing. Pre-swing, however, prepares the limb for
swing advancement and in that sense could be considered a component of
swing phase.
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a) Pre-swing
Pre-swing is the terminal double-limb support period and occupies the
last 12 percent of stance phase, from 50 percent to 62 percent. It begins
when the contra-lateral foot contacts the ground and ends with ipsilateral
toe off. During this period, the stance limb is unloaded and body weight
is transferred onto the contra-lateral limb. The descending portion of the
second peak of the vertical force graph demonstrates the period of preswing.
Terminal contact (TC), a term rarely used, describes the instantaneous
point in the gait cycle when the foot leaves the ground. It thus represents
either the end of the stance phase or the beginning of swing phase. In
pathologies where the foot never leaves the ground, the term foot drag is
used. In foot drag, the termination of stance and the onset of swing may
be somewhat arbitrary.
The termination of stance and the onset of swing is defined as the point
where all portions of the foot have achieved motion relative to the floor.
Likewise, the termination of swing and the onset of stance may be
defined as the point when the foot ends motion relative to the floor. Toe
off occurs when terminal contact is made with the toe.
b) Initial Swing
The initial one-third of the swing period, from the 62- to 75-percent
periods of the gait cycle (6), is spent in initial swing. It begins the
moment the foot leaves the ground and continues until maximum knee
flexion occurs, when the swinging extremity is directly under the body
and directly opposite the stance limb.
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c) Mid-swing
Mid-swing occurs in the second third of the swing period, from the 75- to
85-percent periods of the gait cycle (6). Critical events include continued
limb advancement and foot clearance. This phase begins following
maximum knee flexion and ends when the tibia is in a vertical position.
d)Terminal Swing
In the final phase of terminal swing from the 85- to 100-percent periods
of the gait cycle (6), the tibia passes beyond perpendicular, and the knee
fully extends in preparation for heel contact.
In those cases where the foot never leaves the ground, sometimes
referred to as foot drag,
Double limb support:
is the period of time when both feet are in contact with the ground. This
occurs twice in the gait cycle-at the beginning and end of stance phaseand also is referred to as initial and terminal double-limb stance.
As velocity increases, double-limb support time decreases. Running
constitutes forward movement with no period of double-limb support.
In normal walking, initial double-limb support takes up about 12 percent
of the gait cycle, and terminal double-limb support occupies 12 percent as
well.
Generally, the two periods of double-limb support represent 25 percent of
the gait cycle.
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Single limb support:
is the period of time when only one foot is in contact with the ground. In
walking, this is equal to the swing phase of the other limb.
The term ipsilateral is used to describe the same side of the body, and the
term contra-lateral is used to describe the opposite side of the body or the
opposite limb. The direction of walking is referred to as the line of
progression.
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Determinants of Gait
walking as the translation of the center of mass through space in a manner
requiring the least energy expenditure. They identified six determinants
or variables that affect that energy expenditure.
1) Variations in pelvic rotation,
2) pelvic tilt,
3) knee flexion at mid-stance,
4) foot and ankle motion,
5) knee motion,
6) lateral pelvic displacement.
all affect energy expenditure and the mechanical efficiency of walking.
These determinants of gait are based on two principles:
1. Any displacement that elevates, depresses or moves the center of
mass beyond normal maximum excursion limits wastes energy.
2. Any abrupt or irregular movement will waste energy even when
that movement does not exceed the normal maximum displacement
limits of the center of mass.
Of the six determinants of gait, three provide mechanical advantages that
limit vertical displacement of the center of mass. The term center of mass
is synonymous with the term center of gravity (CG).
Without these mechanical advantages that limit displacement, the center
of mass would displace vertically 7.5 cm (3 inches) on a person of
average height. Resulting from these three determinants, the center of
mass is said to displace vertically only 5 cm (2 inches).
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Pelvic Rotation
The trailing extended weight-bearing limb is elastically linked through
the joints of the pelvis with the advancing swing limb. Ligamentous
constraints and muscular activity combine with forward momentum of
the advancing swing limb to position the pelvis into four degrees of
rotation from the line of progression prior to initial contact
. During the reciprocating contra-lateral swing phase, the pelvis rotates in
the opposite direction, first returning to its neutral position and then
continuing to rotate an additional 4 degrees. Thus the total range of pelvic
rotation is 8 degrees.
In the act of pelvic rotation, both the trailing and advancing limbs are
effectively lengthened through the rotation that uses the pelvic width to
extend both support points. At the very time when the center of mass
would otherwise drop excessively, this rotation prevents .95 cm (3/8inch) of downward displacement of the center of mass.
Figure 8. Pelvic rotation effectively extends the trailing and advancing support
points.
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Pelvic Tilt
At mid-stance, the center of mass reaches its highest point as the body
vaults over a planted leg. It would be even higher were it not for the
pelvis, which tilts down toward the swing side 5 degrees from vertical
(positive Trendelenburg sign) and thus depresses the center of mass .5 cm
(3/16-inch) in an efficient method of energy conservation. This is referred
to as pelvic list or pelvic tilt and is possible only in conjunction with
adequate limb clearance in swing phase
Figure 9. Pelvic tilt reduces vertical displacement of the center of mass.
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Knee Flexion During Mid-stance
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The stance limb enters initial contact with the knee in nearly full
extension. It then flexes as the foot shifts to a plantar-grade position and
continues moving into flexion until it reaches approximately 15 degrees.
The knee then begins to extend but retains some flexion as it nears midstance; due to a relatively less extended knee as the tibia reaches
verticality when the center of mass is at its peak, the summit of the CG is
depressed in its elevation by 1.1 cm (7/16-inch).
To summarize, the .95-cm displacement savings from pelvic rotation, .5cm savings from pelvic tilt and 1.1-cm savings derived from knee flexion
at mid-stance result in a combined displacement savings of 2.1 cm
(approximately 1 inch). Without these three determinants, pelvic rotation,
pelvic tilt and knee flexion at mid-stance, the vertical displacement of the
center of mass is thought to be 7.5 cm (3 inches). With the 2.1 cm savings
derived from these determinants, the vertical displacement of the center
of mass has been reduced to approximately 5 cm (2 inches). If these three
determinants were the only mechanisms affecting the progression of the
center of mass as it traverses through space, the CG pathway would
consist of a series of arcs at whose intersections an abrupt shift in the
direction of the CG would occur as it reached its lowest point. However,
both foot and ankle motion as well as knee motion serve to smooth the
pathway of the CG.
Figure 13. Lateral pelvic displacement improves the position of the center of mass
over the support limb.
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Foot and Ankle Motion
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The most important mechanism to smooth this pathway is foot and ankle
motion. At initial contact, the ankle is elevated due to the heel lever arm
but falls as the foot becomes plantar grade. At heel rise, the ankle again is
elevated, which continues through terminal stance and pre-swing. These
ankle motions, coordinated with the knee and controlled by muscle action
of pretibials and triceps surae, smooth the pathway of the center of mass
during stance phase
The controlled lever arm of the forefoot at pre-swing is particularly
helpful as it rounds out the sharp downward reversal of the center of
mass. Thus it does not reduce a peak displacement period of the center of
mass as the earlier determinants did but rather smooths the pathway. Foot
and ankle motion thus facilitate the path of the CG, keeping it relatively
horizontal throughout stance phase.
Figure 11. Foot and ankle motion smooths the pathway of the center of mass.
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Knee Motion
Knee motion is intrinsically associated with foot and ankle motion. At
initial contact before the ankle moves into a plantar-grade position and
thus is relatively more elevated, the knee is in relative extension.
Responding to a plan- tar-grade posture (when the ankle is depressed), the
knee flexes. Passing through mid-stance as the ankle remains stationary
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with the foot flat on the floor, the knee again reverses its direction to one
of extension. As the heel comes off the floor in terminal stance, the ankle
again is elevated, and the knee flexes. In pre-swing, as the forefoot rolls
over the metatarsal heads, the ankle moves even higher in elevation as
flexion of the knee increases. Generally, at periods when the ankle center
is depressed, the knee extends, and at periods when the ankle is elevated,
the knee flexes. Knee motion, intimately associated with foot and ankle
motion, smooths the pathway of the center of mass and thus conserves
energy.
Figure 12. Knee motion coordinated with foot and ankle motion smooths the
pathway of the center of mass.
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Lateral Pelvic Displacement
To avoid extraordinary muscular and balancing demands, the pelvis shifts
over the support point of the stance limb. If the lower extremities dropped
directly vertical from the hip joint, the center of mass would be required
to shift three to four inches to each side to be positioned effectively over
the supporting foot. The combination of femoral varus and anatomical
valgum at the knee permits a vertical tibial posture with both tibias in
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close proximity to each other. This narrows the walking base to 5-10 cm
(2-4 inches) from heel center to heel center. This reduces the lateral shift
required of the center of mass to 2.5 cm (1 inch) toward either side (see
Figure 13) . The walking base or stride/step width typically is measured
from one ankle joint center to the other although it often is described as
the measurement from heel center to heel center.
A wide walking base may increase stability-but at a cost of energy
efficiency-and the center of mass remains in a box two inches tall and
two inches wide as the individual ambulates forward in normal human
locomotion.
Figure 13. Lateral pelvic displacement improves the position of the center of mass
over the support limb.
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Foot and Ankle Function: The Rocker Mechanisms
Perry has described the function of the heel, ankle and forefoot rocker
mechanisms in normal gait (4). Understanding the natural mechanics of
these rockers greatly improves the abilities to diagnose and communicate
orthotic and prosthetic gait deficits.
The first rocker is referred to as the heel rocker. The momentum
generated by the fall of body weight onto the stance limb is preserved by
this heel rocker. Normal initial contact is made by the calcaneal
tuberosity, which becomes the fulcrum about which the foot and tibia
move. The bony segment between this fulcrum and the center of the ankle
rolls toward the ground as body weight is dropped onto the stance foot,
preserving the momentum of forward progression.
The second rocker is the ankle rocker. The pivotal arc of the ankle rocker
advances the tibia over the stationary foot.
Human locomotion is a phenomenon of the most extraordinary complexity in which
so great are the multitude of individual motions occurring simultaneously in the three
planes of space that analysis is difficult without some unifying principle. The adoption
of the concept that fundamentally locomotion is the translation of the center of gravity
through space along a pathway requiring the least expenditure of energy supplies the
necessary unifying principle which permits of qualitative analysis in terms of the
essential determinants of gait. The six major determinants are pelvic rotation,
pelvic tilt, knee and hip flexion, knee and ankle interaction, and lateral pelvic
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displacement. The serial observations of irregularities in these determinants provides
insight into individual variation and a dynamic assessment of pathological gait.
Pathological gait may be viewed as an attempt to preserve as low a level of energy
consumption as possible by exaggerations of the motions at unaffected levels.
Compensation is reasonably effective with the loss of one determinant of which that at
the knee is the most costly. Loss of two determinants makes effective compensation
impossible and the cost of locomotion in terms of energy is increased threefold with
an inevitable drain upon the body economy
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