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Biomechanics of the Gait : 1 Dr. Dibyendunarayan Bid [PT] The Sarvajanik College of Physiotherapy, Rampura, Surat
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Page 1: Gait Biomechanics 1

Biomechanics of theGait : 1

Dr. Dibyendunarayan Bid [PT]The Sarvajanik College of Physiotherapy,

Rampura, Surat

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IntroductionIn human locomotion (ambulation, gait),

we discover how individual joints and muscles function in an integrated manner both to maintain upright posture and to produce motion of the body as a whole.

Knowledge of the kinematics and kinetics of normal ambulation provides the reader with a foundation for analyzing, identifying, and correcting abnormalities in gait.

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Human locomotion, or gait, may be described as a translatory progression of the body as a whole, produced by coordinated, rotatory movements of body segments.

The alternating movements of the lower extremities essentially support and carry along the head, arms, and trunk (HAT).

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HAT constitutes about 75% of total body weight, with the head and arms contributing about 25% of total body weight and the trunk contributing the remaining 50%.

Walking is probably the most comprehensively studied of all human movements, and the variety of technologies, coupled with the diversity of disciplinary perspectives, has produced a complex and sometimes daunting literature.

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Nevertheless, the biomechanical requirements of the movement that explain gait are logical and easily understood if the detail is not permitted to cloud comprehension.

The purpose of this discussion is to provide this comprehension of gait that will serve as the foundation for analysis of normal walking and of gait deviations.

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General Features In early gait analysis, investigators used

cinematographic film.

Until about 20 years ago, sophisticated analysis required frame-by-frame hand-digitizing of markers that had been placed on body landmarks.

These data were coupled with knowledge of the center of pressure (CoP) of the foot-floor forces derived from a force platform to give complete, if simplified, kinetic information.

This is referred to as the inverse dynamic approach with link segment mechanics.

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Electrogoniometers fastened to joints were also commonly used to describe joint motion and still have applications.4

Similarly, electromyography (EMG) has been used for many decades, although the expectation that it would be possible to convert those signals to force values in simple, useful ways has not been fulfilled.

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The past two decades have witnessed an explosion of technical advancements in motion analysis whose greatest virtue is the ability to collect and process large amounts of data.

As with the development of any science, the knowledge available far exceeds its current applications.

A modern gait laboratory (Fig. 14-1) includes some kind of motion analysis system that gives precise marker locations that are subsequently used to model a several-segment body with joint centers and centers of mass.

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One or more force platforms provide simultaneous foot-floor forces.

EMG systems provide simultaneous information from surface or, sometimes, indwelling electrodes.

An excellent and engaging report of the evolution of clinical gait analysis, including motion analysis and EMG, can be found in Sutherland’s articles.

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To understand gait, let us first identify the fundamental purposes.

Winter proposed the following five main tasks for walking gait:

1. maintenance of support of the HAT: that is, preventing collapse of the lower limb

2. maintenance of upright posture and balance of the body3. control of the foot trajectory to achieve safe ground

clearance and a gentle heel or toe landing4. generation of mechanical energy to maintain the present

forward velocity or to increase the forward velocity5. absorption of mechanical energy for shock absorption

and stability or to decrease the forward velocity of the body

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The professional staff at Rancho Los Amigos National Rehabilitation Center in California identified three main tasks in walking: ◦ (1) weight acceptance (WA), ◦ (2) single-limb support, and ◦ (3) swing limb advancement.

Although worded differently, these concepts correspond to Winter’s first three tasks.

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However, the body moves only because energy is generated by means of concentric contraction of muscle groups.

In fact, normal walking at a constant velocity requires small bursts of energy from three muscle groups at two important times in the gait cycle.

Likewise, unless energy is removed with each step through eccentric muscle contractions, the velocity of walking would continue to increase.

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Gait InitiationGait initiation may be defined as a

stereotyped activity that includes the series or sequence of events that occur from the initiation of movement to the beginning of the gait cycle.

Gait initiation begins in the erect standing posture with an activation of the tibialis anterior and vastus lateralis muscles, in conjunction with an inhibition of the gastrocnemius muscle.

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Bilateral concentric contractions of the tibialis anterior muscle (pulling on the tibias) results in a sagittal torque that inclines the body anteriorly from the ankles.

Initially, the CoP is described as shifting either posteriorly and laterally toward the swing foot (foot that is preparing to take the first step) or posteriorly and medially toward the supporting limb.

Abduction of the swing hip occurs almost simultaneously with contractions of the tibialis anterior and vastus lateralis muscles and produces a coronal torque that propels the body toward the support limb.

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According to Elble and colleagues, the support limb hip and knee flex a few degrees (3 to 10), and the CoP moves anteriorly and medially toward the support limb.

This anterior and medial shift of the CoP frees the swing limb so that it can leave the ground.

The gait initiation activity ends when either the stepping or swing extremity lifts off the ground or when the heel strikes the ground.

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The total duration of the gait initiation phase is about 0.64 second.

A healthy individual may initiate gait with either the right or left lower extremity, and no changes will be seen in the pattern of events.

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Kinematics

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Phases of the Gait CycleGait has been divided into a number of

segments that make it possible to describe, understand, and analyze the events that are occurring.

A gait cycle spans two successive events of the same limb, usually initial contact (also called heel contact or heel strike) of the lower extremity with the supporting surface.

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During one gait cycle, each extremity passes through two major phases:

◦ a stance phase, when some part of the foot is in contact with the floor, which makes up about 60% of the gait cycle, and

◦ a swing phase, when the foot is not in contact with the floor, which makes up the remaining 40% (Fig. 14-2).

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There are two periods of double support occurring between the time one limb makes initial contact and the other one leaves the floor at toe-off.

At a normal walking speed, each period of double support occupies about 11% of the gait cycle, which makes a total of approximately 22% for a full cycle.

The body is thus supported by only one limb for nearly 80% of the cycle. The approximate value of 10% for each double-support phase is usually used.

The approximate value of 10% for each double-support phase is usually assigned to each of the two double-support periods.

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The two most common terminologies for the further division of these major phases into sub phases are shown in Figures 14-3 and 14-4, where one will be referred to as traditional (T), and one derived from Rancho Los Amigos (RLA).

Both terminologies define “events” that mark the start and end of defined sub-phases.

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Figure 14-3 identifies the events delimiting the major phases in both terminology conventions as initial contact (T and RLA) or heel contact or heel strike (T) and toe-off (RLA and T).

In both conventions, the gait cycle is divided into percentiles that will be used to clarify events and phases.

Values for normal walking appear in the figures.

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Events in Stance Phase 1. Heel contact or heel strike (T) refers to the instant at

which the heel of the leading extremity strikes the ground (Fig. 14-5).

The word “strike” is actually a misnomer inasmuch as the horizontal velocity reduces to about 0.4 m/sec and only 0.05 m/sec vertically.

Initial contact (T and RLA) refers to the instant the foot of the leading extremity strikes the ground.

In normal gait, the heel is the point of contact.

In abnormal gait, it is possible for the whole foot or the toes, rather than the heel, to make initial contact with the ground. The term initial contact will be used in referring to this event.

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2. Foot flat (T) in normal gait occurs after initial contact at approximately 7% of the gait cycle (Fig. 14-6).

It is the first instant during stance when the foot is flat on the ground.

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3. Midstance (T) is the point at which the body weight is directly over the supporting lower extremity (Fig. 14-7), usually about 30% of the gait cycle.

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4. Heel-off (T) is the point at which the heel of the reference extremity leaves the ground (Fig. 14-8), usually about 40% of the gait cycle.

5. Toe-off (T and RLA) is the instant at which the toe of the foot leaves the ground (Fig. 14-9), usually about 60% of the gait cycle. 7/2/2012

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Subphases of Stance Phase1. Heel strike phase (T) begins with initial

contact and ends with foot flat and occupies only a small percentage of the gait cycle (see Fig. 14-3).

2. Loading response (RLA), or WA, begins at initial contact and ends when the contralateral extremity lifts off the ground at the end of the double-support phase and occupies about 11% of the gait cycle (see Fig. 14-3).

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3. Midstance phase (T) begins with foot flat at 7% of the gait cycle and ends with heel-off at about 40% of the gait cycle.

Midstance phase (RLA) begins when the contralateral extremity lifts off the ground at about 11% of the gait cycle and ends when the body is directly over the supporting limb at about 30% of the gait cycle,

which makes it a much smaller portion of stance phase than the T midstance phase.

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4. Terminal stance (RLA) begins when the body is directly over the supporting limb at about 30% of the gait cycle and ends a point just before initial contact of the contralateral extremity at about 50% of the gait cycle.

5. Push-off phase (T) begins with heel-off at about 40% of the gait cycle and ends with toe-off at about 60% of the gait cycle (see Fig. 14-2).

6. Preswing (RLA) is the last 10% of stance phase and begins with initial contact of the contralateral foot (at 50% of the gait cycle) and ends with toe-off (at 60%).

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Swing Phase

1. Acceleration, or early swing phase (T), begins once the toe leaves the ground and continues until midswing, or the point at which the swinging extremity is directly under the body (see Fig. 14-3).

2. Initial swing (RLA) begins when the toe leaves the ground and continues until maximum knee flexion occurs.

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3. Midswing (T) occurs approximately when the extremity passes directly beneath the body, or from the end of acceleration to the beginning of deceleration.

Midswing (RLA) encompasses the period from maximum knee flexion until the tibia is in a vertical position.7/2/2012

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4. Deceleration (T), or late swing phase, occurs after midswing when limb is decelerating in preparation for heel strike.

Terminal swing (RLA) includes the period from the point at which the tibia is in the vertical position to a point just before initial contact.

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For most purposes, including patient report writing, it is preferable to refer to events as occurring in early, middle, or late stance phase or in early, middle, or late swing phase.

For detailed description or quantitative analysis, more specific events and phases may be needed,

but it is most important that the student grasp the overall picture and understand the major events of gait,

which can become buried in excessive terminology.

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End of part - 1

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