Improper body alignment limits function, and thus it is a concern of everyone regardless of occupation, activities, environment, body type, sex, or age. To effectively overcome postural problems, therapy must be based upon mechanical principles. In the absence of gross pathology, postural alignment is a homeostatic mechanism that can be voluntarily controlled to a significant extent by osseous adjustments, direct and reflex muscle techniques, support when advisable, therapeutic exercise, and kinesthetic training.

In the health sciences, body mechanics has often been separated from the physical examination. Because physicians have been poorly educated in biomechanics, most work that has been accomplished is to the credit of physical educators and a few biophysicists. Prior to recent decades, much of this had been met with indifference if not opposition from the medical profession.


Posture Analysis

It has long been felt in chiropractic that spinal subluxations will be reflected in the erect posture and that spinal distortions result in the development of subluxation syndromes. Consequently, an array of different methods and instrumentation has been developed for this type of analytical approach such as plumb lines with foot positioning plates to allow for visual evaluation relative to gravitational norms, transparent grids, bubble levels, silhouettographs, posturometer devices to measure specific degrees in attitude, multiple scale units to measure weight of each vertical half or quadrant of the body, and moire contourography.

      OBJECTIVES

Such procedures yield useful information; however, there is a great deal of possible subjective error in the interpretation of findings. Regardless, recorded analyses of body alignment serve as a guide to a patient's holistic attitude, structural balance or imbalance, hypertonicity, need for therapeutic exercises, habitual stance, postural fatigue, basic nutritional status, and they offer a comparative progress record.

      EYE DOMINANCE

One source of analytical error which can be easily corrected is that of eye dominance. It is important to realize that the examiner's peripheral vision is used for judging the body bilaterally. This is true in posture analysis as well as in the physical examination when, for instance, bilateral motion of the rib cage is assessed. If the examiner has a dominant eye, the reclining patient should be observed with the dominant eye over the midline of the patient's body.

Test. An examiner may determine eye dominance by the following procedure:

(1)   hold the index finger of the right hand at arm's length directly in front of the nose at the level of the eyes.
(2)   Place the tips of the left index finger and thumb to form a circle.
(3)   Place this circle directly in front of the nose about elbow distance away.
(4)   Sight the tip of the right index finger in the center of the circle using both eyes.
(5)   Close the left eye to see if the right index finger stays in the center of the circle. If it does, the right eye is dominant.
(6)   Close the right eye to see if the right index finger stays in the center of the circle. If it does, the left eye is dominant.

      INSPECTION

Have the patient stand with his heels together, with his hands hanging normally at his sides. Encourage the patient to stand normally and not try to assume "good posture" or the "military stance". Note body type and then the following checkpoints relative to a lateral plumb line falling just anterior to the external malleolus (See Figure 4.1) and an anterior or posterior vertical line bisecting the heels.

Head and Neck.   From the side, forward or backward shifting of body weight (not normal sway) can be judged by the position of the line from the ear. From the rear, note the position of the patient's head by comparative ear level. If the head is tilted to the right, the chin will tilt to the left. Note the bilateral development of the sternocleidomastoideus and suboccipital muscles. Asymmetrical fullness of the suboccipital musculature indicates upper cervical rotation.

Shoulder Girdle.   From the side, note the prominence, rotation, or tilting of the inferior angles of the scapulae. From the rear, observe the comparative height of the scapulae, comparing one to the other. The cervicobrachial spine is always scoliotic toward the side of the high shoulder. Check for winged scapulae or for scapulae failing to lie smoothly on the chest wall. Note the distance of the scapulae vertebral borders from the spine. The midthoracic spine is always scoliotic toward the side on which the vertebral margin of the scapula is more prominent and flaring. If the shoulder is high on the right and the scapula flares on the right, the entire cervicobrachial and thoracic spine is scoliotic toward the right. If the shoulder is high on the right yet the left scapula flares, the cervicobrachial spine is scoliotic to the right and the midthoracic spine is scoliotic to the left.

Thorax.   From the front, observe any signs of hollow chest, sternal or rib depression, or pathologic signs such as Harrison's groove, funnel chest, barrel chest, or pigeon chest. From the rear, note the contours of the trapezius muscles for normal development or for abnormal tightness or tenderness. Note the angles of the ribs. A difference in the height of the scapulae and the iliac crests usually indicates a scoliosis. Lateral positions of the spinous processes and anterior or posterior positions of the transverse processes together with an elevation of the angles of the ribs indicates a rotation of vertebrae.

Abdomen.   From the side, check the degree of abdominal muscle relaxation. Keep in mind that children normally have a prominent abdomen and adult women have a deposit of superficial fat lying transversely below the umbilicus.

Spine.   From the side, check the curvatures of the spine. Evaluate as normal or abnormal; lordotic or kyphotic. Note the degree of sacral tilt and lumbosacral angle. From the rear, compare the line of the spinous processes. Bear in mind the possibility of a spinous process being asymmetrical, deviated to the right or left, without the body of the vertebra being involved. Evaluate any degree of scoliosis.

Pelvis.   In pelvic mechanical pathologies on the side of involvement, there is a reduction in the height and depth of the body angle as observed from the posterior. A low and less prominent iliac crest will be best observed from the front. Note the comparative height of the iliac crests and greater trochanters. Check the comparative height and depth of the sacral dimples, the position of the gluteal cleft, and the bilateral buttock height. If chronic sciatic neuralgia is on the high iliac crest side, degenerative disc weakening with posterolateral protrusion should be suspected. If it occurs on the side of the low iliac crest, one must consider the possibility of a sacroiliac slip and lumbosacral torsion as being the causative factor.

Legs.   From the side, note the degree of knee hyperextension. From the front, check for any degree of genu valgum or genu varum by the space between the knees. Seek possible tibial torsion or lateral rotation of the tibia (usually unilateral) by noting the position of the patellae.

Feet.   From the rear, note the degree of foot pronation by the line of the Achilles tendon. From the front, check for flattening of the longitudinal arch by noting the position of the navicular tubercles. Seek evidence of hallux valgus or hammer toes.

Postural Changes During Growth

Spinal contour changes drastically during the various stages of maturation. As space becomes limited during the second half of prenatal life, the uterine walls act as restricting barriers to fetal extension. To adapt, the fetus adopts a position of flexion for maximum comfort. This results in a gently kyphotic spinal curve which extends from the atlas to the sacrum (Fig. 4.2).

      FROM BIRTH TO 1 YEAR OF AGE

In the newborn, the spine remains "C" curved; throughout the first year of life, flexor tone is predominant in the extremities in the horizontal position. The first attempt to defy gravity occurs when the baby tries to raise his head in the prone position. This usually becomes successful at about 3 months of age. The first A-P curve develops in the neck as the head is held erect and strength for cervical extension develops (Table 4.1). The ability to roll from prone to supine is usually established by 5 months, and from supine to prone at 6 months. The typical child is able to sit unsupported for the first time between 6 and 8 months. Straightening of the thoracic spine occurs when sitting can be maintained, and the normal lumbar lordosis begins to develop parallel with the ability to walk without assistance at about 13 months.

      BETWEEN 1 AND 2 YEARS OF AGE

During the second year of life, the child learns to stand upright and to balance both A-P and laterally. For stability, he stands and walks with a wide stance to widen the base of support. This is enhanced by diapers, which increase the distance between the upper thighs. During early totter when walking is unsteady, the child leans forward to help forward progression, the legs are partly flexed, and the arms are abducted and slightly flexed at the elbows similar to unfolded wings. By the end of the second year, postural reflexes are well established, allowing for greater skill in propulsion and balancing in the erect position. At this age, the legs will be held closer together, but there will still be a degree of flatfootedness, a prominent abdomen, and an exaggerated lordosis.

      BETWEEN 2 AND 6 YEARS OF AGE

Between the ages of 2 and 6 years, the necessity for lateral balance is maintained by torsion of the tibia. This is exhibited by a degree of knock-knees which should correct itself by the age of 6. The abdomen becomes less prominent, and the foot develops a longitudinal arch. Height increases steadily, but at a constant rate. During the early years of school, the child's posture is one of extreme mobility. The knees may show distinct hyperextension in standing, the pelvis is tilted downward and forward 30°–40°, the abdomen protrudes, the lumbar area is usually lordotic, but may lean back sharply from the lumbosacral area, the scapulae are braced back by the trapezius muscles, often winged, the dorsal area is mildly kyphotic, and the buttocks protrude. A mild "sway-back" condition during this developmental stage should not be confused with a developmental defect.

      EARLY LOCOMOTION

Bipedal locomotion appears to be a learned skill rather than an inherited reflex. According to Inman, et al, a child that is blind at birth never attempts to stand or walk unless carefully trained to do so. Without assistance, such a child will travel as a quadriped, coordinating his or her four limbs so that three limbs are on the floor at the same time to offer the stability of a tripod. Thus, walking upright can be considered a trial-and-error translational learning process. This translation is the product of measurable angular displacements of body segments about joint axes.

The characteristic walking pattern of the adult is not acquired until the child is about 7-9 years of age. Prior to this, the child conducts progressively difficult neuromusculoskeletal experiments that tend to improve neural control of motor skills that help to modify segmental displacements.

      PUBERTY

Prior to puberty, the limbs grow faster than the trunk. The rate of trunk and extremity growth is about the same at puberty. The trunk continues to grow after the extremities slow their rate of growth in the postpuberty period. This changes the ratio of sitting to standing height. Sitting height is about 70% of total height at birth and about 52% for 16-year-old girls and 14-year-old boys. Thus, postural adjustments must be made during the growth period to adapt to gravitational forces (Figs. 4.3 and 4.4).

      ADOLESCENCE

During the adolescent spurt of growth, changes in body proportions occur to adjust to gravity. The pelvic tilt decreases to 20°–30°. The knees are slightly bent, but the earlier hyperextension is not necessary to balance a prominent abdomen. Posture becomes less mobile, and the postural patterns become stabilized. If proper adaptive mechanisms fail, an adolescent "round shoulders" condition may be present with a neck projected forward and a head that is extended.


Gravitational Forces

The success that a person has in meeting the constant stress of gravity may have a subtle yet profound influence on his or her quality of health and performance. While gravity stabilizes the lower extremities in standing and provides friction for locomotion, it also places considerable stress on those body parts responsible for maintaining the upright position. Without appropriate neuromusculoskeletal compensation and accommodation, such actions result in imbalance and often falling. Thus, postural deviations resulting in balance problems lead to frequent strain and injury to antigravity structures.

      CENTER OF GRAVITY

As gravity acts on all parts of the body, one's entire weight can be considered as concentrated at a point where the gravitational pull on one side of the body is equal to the pull on the other side. This point is the body's center of gravity, and it constitutes the exact center of body mass (Fig. 4.5). When the center of gravity is above the base of support and the pull of gravity is successfully resisted by the supporting members, an equilibrium of forces or a state of balance is reached and no motion occurs.

In a model subject, the center of gravity is located in the region just anterior (about 1|") to the top of the second sacral segment; ie, about 55% of the distance for women and 57% for men, from the plantar surfaces to the apex of the head in the erect position. Its location will vary somewhat according to body type, age, and sex, and move upward, downward, or sideward in accordance with normal position movements and abnormal neuromusculoskeletal disorders.

The accumulation of fat and the loss of soft tissue tone are common factors in altering one's center of gravity. Thus, the center of gravity shifts with each change in body alignment, and the amount of weight borne by the joints and the pull of the muscles vary within reasonable limits with each body movement. Adequate compensation is provided for in the healthy, structurally balanced person.

      LINE OF GRAVITY

Reference Points.   The vertical A-P line of gravity of the body, as viewed laterally in the erect model subject, falls from above downward through the earlobe, slightly posterior to the mastoid process, through the odontoid process, through the middle of the shoulder joint, touches the midpoint of the anterior borders of T2 and T12, then falls just slightly anterior to S2, slightly behind the axis of the hip joint, slightly anterior to the transverse axis of rotation of the knee (slightly posterior to the patella), crosses anterior to the lateral malleolus and through the cuboid-calcaneal junction to fall between the heel and metatarsal heads. When viewed from the back, the lateral line of gravity passes through the occipital protuberance, the C7 and L5 spinous processes, the coccyx and pubic cartilage, and bisects the knees and ankles. Thus, the A-P and lateral lines of gravity divide the body into four quarters (Fig. 4.6).

Plumb Line Analysis.   The plumb line, as used in postural analysis, serves as a visual comparison to the line of gravity. For example, when the plumb line is centered over S1, it should fall in line with the occipital protuberance. In uncompensated scoliosis, however, it will be seen to fall lateral to the occipital protuberance.

Weight Bearing.   The most economical use of energy in the standing position is when the vertical line of gravity falls through a column of supporting bones. If the weight-bearing bony segments are aligned so that the gravity line passes directly through the center of each joint, the least stress is placed upon the adjacent ligaments and muscles. This is the ideal situation, but it is impossible in the human body because the centers of segmental links and the movement centers between them cannot be brought to accurately meet with a common line of gravity.

Stability.   Since the body is a segmented system, the stability of the body depends upon the stability of its individual segments. The force of gravity acting upon each segment must be individually neutralized if the body as a whole is to be in complete gravitational balance. That part of balance contributed by an individual segment is called the segment's partial equilibrium, as contrasted with the total equilibrium of the whole body. Thus, each segment has its own partial center of gravity and partial gravity line.

Position Changes.   Any change in position of a partial center of gravity produces a corresponding change in the common center of gravity. When the arms are raised overhead and lowered, the center of gravity is respectively raised and lowered within the body. When the arms are stretched forward or backward, the center of gravity is respectively moved anteriorly or posteriorly within the body. When the trunk is flexed severely forward or laterally, the center of gravity shifts outside the body.

      BODY BALANCE AND EQUILIBRIUM

Active and Passive States.   Positions of the body that require muscular forces to maintain balance are said to be in active equilibrium, while those that do not require muscular effort are in passive equilibrium. In passive equilibrium, all segmental centers of gravity and the centers of all joints fall within the gravity line of the body which must fall within the base of support. This requires complete neutralization of all linear and rotary components of gravitational force by joint surfaces and the base of support. Thus, such a state is impossible in the erect position but possible in the horizontal position.

Balance.   When the forces of gravity on a body are in a balanced position, the pull is equal on all sides about the center of gravity; ie, its center of gravity is directly above its base of support and the body is quite stable (Fig. 4.7). The amount of body mass outside this base does not affect the equilibrium unless the center of gravity of the mass is altered. If a part is laterally shifted to one side without a compensatory shift of another part of equal weight, the center of gravity is displaced sideward. The body will topple if the center of gravity is displaced outside its base of support because gravity pulls greater on the side of weight displacement. Because males generally have a larger thorax, broader shoulders, and heavier arms than females, they are toppled with less force than are females of the same size.

Common Torques.   In the body, all partial centers of gravity or their axes of motion do not coincide with the common line of gravity. In fact, many partial centers are quite distant from the common line, and this causes active rotary torques in many joints because of gravitational pull which must be neutralized by antigravity muscles. A weight-bearing joint is considered to be in equilibrium if the gravity line of the supported structure is equal to the joint's axis of rotation. If the gravity line is posterior to the joint's axis of rotation, the superior segment tends to rotate posteriorly in compensation. If it is anterior to the axis, the superior segment tends to rotate anteriorly.

Toppling Rate.   The rate of movement of an unbalanced body which is toppling depends on the amount of lateral displacement of the center of gravity from its base of support. For this reason, a toppled tree falls slowly at first because of trunk resistance and then rapidly as its center of gravity is further displaced from the tree trunk. A tall person falls harder than a short person. For the same reason, the further the body's center of gravity is displaced from the midline of its base of support, the more force is necessary to return it to the balanced position.

      ACTION LINES

Segmental weight offers resistance to movement as gravity is acting on the part only in a downward direction with the part's mass acting as if it were at its center of mass (Fig. 4.8). The effectiveness of this weight for rotating a part can be changed by shifting its position in relation to the fulcrum, because the farther the gravity line falling through the center of mass is from the axis of motion, the longer will be the moment arm and the greater will be the moment.

During motion, the gravitational action line of a part can be moved near to or away from the axis of a joint simply by changing the part's position. For example, it is easier to raise a flexed leg in the horizontal position than a straight leg. This flexion does not change the limb's weight. The straight knee increases the moment of the gravitational force because the distance from the action line of the gravitational force on the hip has been shortened. For the same reason, it is much easier to do situps with the hands at the sides than when the hands are extended overhead.

Clinical Applications.   These principles are commonly applied in therapeutic exercises. They are also applied in muscle testing and muscle stretching procedures. In muscle testing, resistance applied at the most distal aspect of the segment gives the resistance force a better lever arm and greater advantage than one applied more proximal. In muscle stretching, a much more proximal grip should be taken. This reduces the chance of joint or soft-tissue injury and affords better control of the movement.

Stabilization Mechanisms

Electromyograph studies have shown that very little muscle activity is required in the normal relaxed standing position. Most action involves those muscles that act around the ankle. The minimal activity necessary is attributed to the elastic properties of muscle, joint locking, and the tension from the passive stretch of muscles, ligaments, and fascia which act prior to muscle contraction of joint stabilizers.

The body's stability is greatest when its center of gravity is low and its base of support is wide. Knee and hip joints are fully extended during weight bearing, and the knee joint "screws home" by slightly rotating on the fully extended joint to provide firm joint locking.

      POSITION OF THE CENTER OF GRAVITY

The closer the body's center of gravity to its base of support, the more stable it is: resisting moment = weight X distance. That is, the stability of an object is indirectly proportional to the height of its center of mass above its base. For example, a book laid flat upon a table is difficult to upset as compared to one standing on a narrow end.

      SIZE OF THE BASE OF SUPPORT

Both the size and position of the base of support are important in maintaining equilibrium. Regardless of toe position in the standing position, stability is provided if the gravity line falls approximately midway along the base of support. That is, the body is stable until the center of gravity falls perpendicularly outside the base of support. The larger the base of support, the greater displacement of the center of gravity from a midpoint before balance is lost. The use of a cane or crutches increases stability because they provide an increased base of support.

Stance and Stability.   The erect body is a poorly engineered model from a strict biomechanical viewpoint because the heavier portions are placed upon a narrow base of support, similar to an inverted cone. Obviously, this position is far less stable than that of the four-legged vertebrates. When the feet are parallel and close together, the upright body is least stable. When a chiropractor delivers an adjustment, a wide stance enhances his stability to the resistance force. Likewise, balance is maintained during reaching and stooping when one foot is advanced to the other. When standing on a ship deck or moving bus, stability is improved by widening the stance. Thus, during stance and locomotion, stability varies greatly as the feet are placed closer together, further apart, or at an angle to each other to increase or decrease the size of the base of support.

Segmental Bases.   Each segment in an articulated system rests upon the one beneath it. The interposed joint surfaces serve as the support base of the separate segments. From this viewpoint, one can see that joint stability is partially dependent on:
(1)   the size of the joint surfaces,
(2)   the height of the segmental centers of gravity above the joint surface, and
(3)   the horizontal distance of the common gravity line to the joint's center.

Head Weight.   The head has a small base of support; ie, the atlas. In the erect position, the relatively small atlas must provide an upward push equal to the weight of the head plus added weight such as that of a hat, helmet, glasses, etc. In a 200-lb person, the atlas offers about a 14-lb resistance force to the skull (Fig. 4.9). When the occiput is tilted so that its center of mass is not in line with both atlantal articulations, cervical muscles opposite to the direction of tilt must contract to maintain equilibrium. The muscles and ligaments at the base of the skull serve to check the compression and shear forces. When these mechanisms fail, a degree of subluxation must result. A similar situation occurs in the lower back where a great deal of weight is borne by the L5 vertebra.

      BALANCE SWAY

In most joints, the line of gravity is not identical to the center line of the joint; ie, most joint centers are some distance from the weight line. This requires constant muscle forces to combat rotational forces to maintain equilibrium by equalizing all translational and torque forces. Even when there is no movement, the antigravity muscles cannot be at rest. To maintain balance, the body is slightly but constantly swaying involuntarily anteroposteriorly, laterally, diagonally, and in rotation.

The body is always in motion. Minute oscillatory movements occur in all body parts, whether awake or asleep, and gross movements are not started until they are in phase with normal oscillations.

Control.   The normal A-P sway of the body is controlled essentially by slight intermittent soleus and tibialis anterior action. The neuromechanisms are not completely understood, but one theory holds that body sway is under intermittent autonomic control: a geotropic reflex said by some to be initiated by position shifts which stretch antigravity muscles and stimulate tonic contractions to bring the joint towards balance.

Direction and Rates.   Most sway occurs near the A-P plane. During A-P sway, weight is invariably anterior to the axis of hip, knee, and ankle. It is composed generally of slower and larger movements as contrasted with other oscillations. In the average mature adult, it has almost a 1-5/8-inch range. Lateral sway has about a 1-1/8-inch range. Body sway is generally to that degree sufficient to produce stimuli to evoke a righting reflex.

Shifting.   During prolonged stance, normal body sway is altered. Weight is distributed symmetrically only 25% of the time, with a mean time factor of a half a minute. This periodic shifting allows intermittent rest periods for the antigravity tissues. However, certain occupations and other physical attitudes may by necessity interfere with this shifting, and this may contribute to postural distortions.

Functional Effects.   The frequent contraction and relaxation of the postural muscles during sway and minute weight shifting has a beneficial influence in milking blood and lymph through the muscles. In this manner, circulation is assisted. The working fibers are supplied with nutrients and are helped from becoming choked by their own metabolic wastes.

Static Stance and Sitting Postures

The term static posture is used in its relative sense, referring to a position of rest as contrasted to one of gross movement. As discussed previously, the body is always dynamic because of such factors as body sway, respiration, and restless shifting.

      INDIVIDUAL DIFFERENCES IN STANCE POSTURE

Racial Differences.   Certain races tend to have characteristic rigid or relaxed static postures accompanied by various degrees of kyphosis and/or lordosis. These postures appear to be related to differences in nutrition, climate, training, and social customs.

Weight.   Body weight has a distinct influence on the erect posture. The obese have the most erect posture as a result of supporting the load over the relatively small base of support. This posture features twisting while walking with short, stiff steps. A large abdomen requires a compensatory posterior torso leaning and acute lumbosacral angle to balance the anterior weight. More weight is borne by the heels. Conversely, the slim person may assume an overly relaxed stance.

Height.   A short person tends to have an erect posture in an attempt to appear taller. This is especially true in the short stocky person because the erect posture tends to make the physique both taller and slimmer. Conversely, the especially tall individual often slouches to appear shorter by developing a habitual kyphosis and knee flexion.

Military Postures.   The military position of attention is an unnatural, immobile position where the chin is drawn in, the neck and chest are elevated, the scapulae are rotated towards the spine, the spine is held vertical, the abdomen is sucked in, the pelvis is tilted posteriorly, and the feet are placed close together with body weight distributed bilaterally. In this position, considerable stress is placed on the erectors of the back and the extensors of the hip and calf. The knee extensors are more relaxed because the center of gravity falls more anterior to the axis of the knee joint. This posture is difficult to maintain for long periods because of the constant muscular tension and the functionally impaired circulation, which can result in pooling within the lower extremities that leads to cerebral anemia.

Pelvic Tilt.   In the typical relaxed stance, pelvic weight falls anterior to the gravity line and trunk weight falls posterior to the gravity line. The degree increases in proportion to the degree of "sway back" present. In contrast, during a tensed stance (eg, military posture), trunk weight is placed further posteriorly and balanced over the hips in the sagittal plane. This state is also seen in a patient with a flattened lumbar region where the pelvis has rotated posteriorly.

Effects of Pregnancy.   During the advanced stages of pregnancy, the center of gravity is displaced considerably forward from the normal because of the increased anterior weight from the fetus, amniotic fluid, and enlarged uterus. Postural compensation is made similar to that seen in the obese with a large abdomen, but there is a more exaggerated compensatory backward lean which is adapted to by a customary upper torso slouch.

Effects of High Heels.   As heel height is increased, the center of gravity is moved posteriorly. When the calcaneus is elevated about a half inch above the level of the base of the ball of the foot, its shaft is brought to a tangent with the Achilles tendon. Thus, the gastrocnemius and soleus are able to exert a greater force in plantar flexion. High heels, habitually worn, tend to shorten these muscles and stretch the anterior ankle muscles.

Occupational Effects.   Habitual strenuous work results in postural adaptations due to the over development of asymmetrical musculature or to asymmetries between one part of the body and another.

Shoes.   As mentioned, prolonged standing with little movement results in lower extremity pooling. The local effect is that the feet may increase up to aboutwo sizes. A common adaptation is the wearing of loose fitting shoes, but this encourages pronation. A well-fitted shoe should be constructed so that most of the weight is borne on the outside of the foot, which is supported by strong ligaments. The inside of the foot is supported by long thin muscles which easily fatigue and allow the arch to drop and the foot to pronate.

Standing Surfaces.   An elastic floor surface, as opposed to a hard surface, becomes slightly compressed by body weight to exert a continual force against the foot in an attempt to recover its original shape. Thus, change of position is assisted by an elastic floor surface.

      POSTURES OF READINESS

The anticipation of a forthcoming event affects one's static posture, and the position assumed is in accord with the immediate goal at hand to be achieved (Fig. 4.11). When one is about to perform a rapid or strong movement, the posture of readiness is an alert one, reaching its peak between 1 and 2 seconds after thought is concentrated on the situation. After this peak, posture either becomes relaxed or becomes unstable because of an exaggerated tremor resulting from fatigue of the coordinating centers of the nervous system. If no action is anticipated or if the environment is nonexciting, the result is a relaxed posture. This posture is so well recognized that the relaxed posture is often used in sports as a ploy to deceive an opponent.

Applications.   During a posture of alert readiness, the center of gravity is shifted toward the anticipated direction of movement. There is a slight head and plantar flexion that causes equilibrium instability to facilitate this shift. Then arm and leg positions are adjusted to the action which is to follow. The baseball infielder leans forward and rises on his toes as the ball is pitched. The base runner taking a lead off a base will also lean toward the next base and rise on his toes as the ball is pitched. The football quarterback crouches with arms forward and heels and hands together in a position of readiness to catch the ball. Somersaults are started forward and backward by a throw of the head. In each instance, the mechanical equilibrium of the body is disturbed and movement is started.

Proprioceptive Mechanisms.   Postures of alert readiness should not be held motionless for a long period because proprioceptive sensations which govern position sense and the relationship of body parts will be diminished and must be reestablished before accurate movement can be achieved. It is for this reason that the golfer and batter waggle their club while adjusting position.

Stability vs Balance.   Postures of alert readiness are often superimposed on postures adapting to mechanical forces. Most movements involve lateral shifts of weight which disturb balance and require the application of opposing forces to regain balance. Postural shifts of the body's center of gravity in the vertical direction alter stability but not balance. An ice skater racing forward in the straightaway leans forward to maintain equilibrium between gravitational force and the driving action of the legs. If the torso is held erect, the driving action of the legs should soon topple the skater backward. When skating around a curve at high speed, the skater must lean forward to compensate for the driving action of his legs and lean toward the inside of the curve to counteract centrifugal forces.

The Stance Phase.   About 60% of the walking cycle is used in the stance phase. Because the stance phase is the weight-bearing phase requiring the greatest stress, most problems will become apparent in its analysis. The stance phase is subdivided into:

(1)   heelstrike,
(2)   footflat, and
(3)   toe pushoff.

Midstance is that weight-bearing period between footflat to toeoff. The duration of gait is usually measured from heelstrike to heelstrike, but any two identical points can be taken.

The Swing Phase.   This is subdivided into:

(1)   initial acceleration,
(2)   mid swing, and
(3)   final deceleration --depending upon the intent.

The swing phase, about 40% of the gait cycle, begins with toeoff and ends with heelstrike. Midswing represents the transition period between acceleration and deceleration.


      BODY OSCILLATION

A wheel is efficient in forward translation because its center of mass is kept parallel to the ground. In the human, however, there is considerable up and down, side-to-side, and rotational oscillation as well as linear translation (Figure 4.20). Thus, force is required for vertical, lateral, and rotational displacement that must be added to the force necessary for forward movement. Any disorder that increases oscillation is energy consuming and linear speed reducing.

High Points.   As previously explained, the center of mass of the body is that point where the mass movements on one side of any plane are equal to the mass movements on the other side. During gait, the high point of vertical oscillation (about 2 inches) and lateral displacement are reached when unilateral weight is greatest and the lower extremity is in full extension. This occurs near mid-stance of the single-supporting limb and midswing of the non-weight-bearing limb. Also, the highest point in elevation of the center of mass occurs when body velocity is lowest, and vice versa. This upward movement begins just after the center of mass has passed anterior to the weight-bearing foot as the body's momentum carries the body up and over the leg in stance. Immediate fall of the center of mass after it has passed over and in front of the weight-bearing foot is delayed by the relative lengthening of the weight-bearing leg via knee extension, ankle plantar flexion, and foot supination. These mechanisms tend to produce a smoother translational pathway.

Low Points.   The low point is reached when the distance between the two feet is greatest --ie, during the middle of double-support bilateral weight bearing. The greater the stride length, the greater the vertical excursion. This low point where both feet are in contact with the ground, one foot at toeoff and the other at heelstrike, normally accounts for 15% of the gait cycle. This is the period of double support, and its duration shortens as walking speed increases. In running, the period of double support is zero.

Stress Points.   The depth of the low point depends on the degree of pelvic rotation and lateral shifting during the period of double support, while the height of the high point depends on the degree of pelvic tilt and knee flexion during footflat. The high point places stress on both the weight-bearing hip and knee; the low point places stress only on the hip as the knee is relatively locked in extension. Flattening the arc of the body's center of mass during translation is maintained by three basic elements:
(1)   pelvic tilt, which depresses the high point;
(2)   pelvic rotation, which elevates the ends of the arc; and
(3)   knee flexion, which also reduces the high point.

Pelvic Tilt.   During normal gait, the pelvis lists coronally downward a few degrees (4°–6°) away from the leg in stance and toward the leg in swing from the force of gravity (positive Trendelenburg). This alternating angular displacement at the hip joint is maximum at midswing on the side of the swinging leg. Pelvic tilt is essentially controlled by contraction of the hip adductors of the stance side. By dipping the center of gravity, it has an effect of minimizing (flattening) the summit of the vertical oscillation arc during gait. The knee of the leg in swing must flex so that the foot will clear the floor. Tilting appears exaggerated in the female because of the wider pelvis and greater superficial fat.

Pelvic Rotation.   Relative to the line of progression, the pelvis alternately rotates toward the right and left about a vertical axis during typical gait. This somewhat stabilizes the center of mass by reducing abrupt changes in oscillation arcs which tends to reduce the severity of impact at surface contact. During hip extension and flexion, angular displacement is reduced and the force necessary to change direction of the body's center of mass in the following arc of translation is reduced. Pelvic rotation occurs anteriorly on the side of the advancing limb during the swing phase and posteriorly during midstance. These alternating rotations occur essentially at the hip joints due to the relative rigidity of the pelvis. The movement is maximum just before heelstrike, moving 3°–5° on either side of the central axis. As speed is increased, this value increases because there is a corresponding increase in stride length.

Pelvic rotation in the transverse plane on a fairly level surface has long been known to be an instinctive energy-saving mechanism because it increases stride length with minimal effort during gait. This mechanism of pelvic rotation has been considered by some to be lost during the metabolically expensive exercise of walking or running uphill or downhill. Wall and associates, however, have shown that this belief is not true. (142) Data recorded from subjects walking on a treadmill that had been sloped plus or minus 20% showed that pelvic rotation on a 20% incline was substantially the same as that on a level surface.

Lateral Sway.   Besides pelvic tilt and rotation, a degree of alternating horizontal displacement occurs to replace the gravity line nearer the hip of stance (Figure 4.21) during the period of single support. Its rhythm is one-half the frequency of vertical displacement. It reaches its greatest degree following midstance on the weight-bearing leg and constitutes about a 2-inch lateral movement of the center of mass with each complete stride. This is seen as an adduction movement of the stance side, as is pelvic tilt. Once its peak of lateral displacement is reached, the pelvis begins to reverse direction. This horizontal sway increases the base of support about 4-8 inches as the feet pass each other. There is normally a slight degree of genu valgum that allows the leg to remain essentially vertical and the feet close together during gait hip movements. When the lateral distance between the feet is increased or decreased, the degree of lateral sway is increased or decreased.

Hip and Knee Flexion and Extension.   The high point of vertical oscillation is also minimized by slight flexion of the hip and knee during midstance. This flexion moves the gravity line anterior to the hip and posterior to the knee. The greater the degree of this flexion, the greater effort is necessary by the hip and knee extensors to maintain equilibrium. During a walking cycle, extension and flexion occur alternately. Knee extension (nonlocking) occurs at heel-strike. Following heelstrike, slight flexion occurs and continues through midstance. Midstance is followed by extension, and then flexion occurs again during pushoff and swing. The knee joint is almost fully extended at heelstrike and then begins to flex to about a maximum of 15° until footflat. Just prior to full weight bearing, the knee again passes into extension. Note that the center of mass is in a state of dropping at the point of heelstrike. This drop is decelerated by slight knee flexion against quadriceps resistance.

Ankle and Foot Flexion and Extension.   At the ankle, dorsiflexion, plantarflexion, and rotation occur alternately during a gait cycle. The ankles display maximum dorsiflexion at the end of stance and maximum plantar-flexion at the end of pushoff. The ankles rotate forward in an arc around the radius formed by the heel at heelstrike and about a center point in the forefoot at pushoff. That is, the foot is plantar flexed against tibialis anterior resistance after heelstrike around a point where heelstrike occurs. Rotation about this point tends to shorten the leg relatively and causes the ankle to be carried slightly forward until footflat is achieved. Deceleration of these movements is the result of quadriceps contraction acting on the knee and tibialis anterior contraction acting on the foot. Added to these mechanisms is the fact that the ankle pronates slightly during full weight-bearing midstance. During a typical walking cycle, heel elevation changes are about twice that of the ankle and toes, while ankle and toe changes are 2-3 times those of the knee and hip.

Thigh and Leg Rotation.   There is a slight medial (clockwise) rotation of the femur at the hip and knee during swing and from heelstrike to near midstance. This is followed by a change to lateral (counterclockwise) rotation which continues through stance to pushoff. That is, the thigh and leg reach their maximum clockwise rotation at heelstrike of the opposite limb and their maximum counterclockwise rotation during stance. There is a close relation between stride length and the degree of thigh/leg rotation. As opposed to arm swing, these transverse rotations of the thigh and leg are in phase with pelvic rotations and increase progressively in degree of displacement from below upward. As with the pelvis, the thigh and leg begin to rotate internally toward the leg in stance as the swing phase begins, and this rotation continues during double weight bearing. However, at midstance the leg abruptly begins to rotate externally, and this external rotation continues until the next swing phase is initiated.

Arm Swing and Spinal Rotation.   Although swinging the arms has no effect upon shifting the center of mass during body oscillation, it provides a means of neutralizing total angular momentum (Figure 4.22). That is, the leg advance and pelvic rotation that produce an angular momentum to the lower body are balanced by a reverse angular momentum of the upper body aided by arm swing resulting from shoulder rotation. During normal gait, these rotations are about 180° out of phase with rotation of the pelvis. That is, maximal forward arm swing occurs contralateral to swing, and backward arm swing occurs contralateral to stance. This helps to control weight over the stance hip, maintain forward momentum, and smooth forward progression of the body as a whole. The inertia of the arms is overcome essentially by the alternating lumbar rotation towards the side of the low pelvis which is compensated by a reverse rotation of the thoracic spine.

Vertebral Motion.   Because of out-of-phase shoulder and pelvic rotations during gait, there must be points of minimum and maximum transverse rotation. Keep in mind that the pelvis rotates anteriorly and the shoulder rotates posteriorly on the side of the swinging leg, and vice versa. Studies have shown that the upper thoracic vertebrae rotate to a degree about equal to that of the shoulder girdle and the lower lumbar vertebrae rotate to a degree about equal with the pelvis. The point of rotational transition, and the site of greatest rotation between vertebrae, is typically between T6 and T7. When weights are carried in the hands, however, this point of transition tends to move upward.

Ankle Rotation.   When the foot is free during the swing phase, the toes point inward on plantar flexion and outward on dorsiflexion. When the foot is fixed on the surface during stance, relative plantar flexion produces external rotation of the leg and dorsiflexion causes internal rotation. The primary mechanism here is the subtalar joint, a single-axis hinge joint whose axis is inclined about 45°, which allows transverse rotation of the tibia. Without this, the foot would have to slip upon the walking surface. It is interesting to note that the foot must change from a flexible structure at the beginning of stance to a rigid lever at pushoff.

Foot Rotation.   The foot tends to rotate medially after heel strike and prior to flatfoot. Pronation occurs as the foot is increasingly loaded. When body weight is transferred from the heel to the forefoot during stance and the person rises on his metatarsal heads prior to pushoff, the heel inverts, the foot supinates, and the leg rotates externally. This raises the longitudinal arch medially and depresses it laterally, tending to shift body weight laterally during maximum weight bearing. At pushoff, the foot deviates laterally to distribute weight between all the metatarsal heads. Evidence of this is shown by the oblique crease in the shoe where the vamp and the cap join. This crease is over the metatarsophalangeal joints and will vary with individual differences in the long axis of the foot and the angle of the metatarsal heads.

Added Loads.   Vertical displacement and length of stride are decreased when the walking individual is carrying a load. Body weight shifts laterally to relieve the load over the oscillating leg (Fig. 4.23). The knees and hips are flexed to decrease vertical oscillation and to reduce the jar at footstrike. It is also for these factors that obese people tend to walk with a waddle. A mother often carries a young child between her hip and ribs (or on the lower back or top of the head in some cultures) as this is the most economical position for the added load.

      EFFECT OF MANIPULATION ON GAIT

A surface electromyographic study conducted by Hibbard found that significant amplitude changes occurred in the electrical activity of gait muscles following manipulation of the lower extremity articulations to reduce malposition, while the electrical activity of control subjects decreased only slightly. (145) Hibbard also cites the work of Rebechini-Zasadny and associates that had earlier found a significant difference in the electrical activity of peripheral muscle following manipulation of just the cervical spine.


Examination of Gait

Every person has a gait, or manner of progressive locomotion, which is peculiar to that individual. However, there are also various modes of walking peculiar to certain diseases which are important diagnostic clues. The range of movements in the lower extremities assists in recognizing specific diseases and helps the doctor of chiropractic determine postural changes resulting from an unnatural gait. For instance, a shortened leg gives a characteristic limp. A stiff knee causes the affected limb to swing outward while walking. Intermittent claudication or limping is observed in chronic peripheral vascular diseases such as endarteritis because muscular activity requires more blood than muscular inactivity.

As the walking gait is the most fundamental form of dynamic posture, it should form the basis of holistic biomechanical analysis. In health, most locomotive adjustments are conducted at an unconscious level. This is not true with the patient suffering a neuromusculoskeletal disability affecting gait. Every motion may require a frustrating conscious effort such as that taken by a healthy person stepping into a canoe where the support is unfamiliar.

Although children emulate adult gait in many respects, there are differences that must be considered in analyzing a pathologic or functionally impaired gait during childhood. Foley and associates, utilizing a TV-computer system of data gathering and analysis, found that joint-angle ranges were the same in children as those of adults.5(155)4 However, accelerations, velocities, and linear displacements were consistently larger for children aged from 6 to 13 years (mean value 10.2) than were adult values.

      SITTING AND ASCENT

During examination, have the subject sit in a chair, arise, and then walk across the room if you have not had an opportunity to witness this previously. The chair should be one that gives firm sitting support and provides for 90° flexion of the knees and hips.

While the patient is sitting, note from the front the patient's sitting balance, levelness of ears, shoulders, and pelvis. From the side, note head, shoulder, and pelvic carriage. Observe how the patient rises from the chair to the standing position. Note the needed base of support: how far the knees are apart and how far the forward foot is from the back foot. If the chair has arms, note the degree the hands are used from sitting to standing to assist weak knees, weak hip extensors, or to maintain stability, balance, and coordination.

      NORMAL STANCE AND SWING PHASES

Noting a gait deformity and in what phase it occurs is most helpful to diagnosis. Many subtle but significant points are frequently missed in the fully clothed patient, thus the patient should be minimally clothed and examined in a private environment. Immediately after analysis, make a graphic or mental record of your impressions of the subject's gait. Osler, the great diagnostician, warned that more can be learned by observing the body in dynamic action than can be learned upon the autopsy table when it is too late to help.

During normal ambulation, the normal range of motion at the ankle is from 20° plantar flexion to 15° dorsiflexion. The knee moves 65° from flexion to extension. At the hip, about 6° of adduction occurs and a 45° range is necessary from flexion to extension.

After the walking sequence has been initiated, the movements are normally continued in a rhythmic manner solely by reflex actions. The stretch reflex of the antagonistic extensor muscles is reflexly inhibited as the flexors of the hip, knee, and ankle are stretched. Walking actions are maintained by the reflexive interplay of muscles acting around the joints in motion (Fig. 4.24).

During the stance phase, the heelstrike to footflat, footflat to midstance, midstance to heeloff, heeloff to toeoff, toeoff to midswing, and midswing to heelstrike actions should be analyzed. During the swing phase, which is only about a third of the cycle, the acceleration to midswing and midswing to deceleration actions should be analyzed.

      HEELSTRIKE

Inspection.   At heelstrike, the ankle is between dorsiflexion and plantar flexion, the knee is fully extended, the hip flexes to about 25°, and the head and trunk are vertical. The right arm is posterior to the midline of the body with the elbow extended, and the left arm is anterior to the midline with the elbow partially flexed. The pelvis is slightly rotated anteriorly, the knee is extended, and the leg is vertically aligned with the pelvis. The foot is near a right angle to the leg on the side of heelstrike, and the plantar surface of the forefoot is visible from the front (Fig. 4.25).

Mechanisms.   The reactive force of the ground tends to plantar flex the foot so that a large surface contacts the ground, to flex the knee, and to drive the hip into greater flexion. This reactive force is checked by extensor action of the joints involved; ie, contraction of the ankle dorsiflexors, eccentric quadricep contraction at the knee, and contraction of the gluteus maximus and hamstrings at the hip. These mechanisms prevent flexion collapse under body weight and absorb the impact jar at heelstrike. There is also some contraction of the posterior hamstrings at heelstrike, but this is considered only to prevent hyperextension of the knee.

Joint Reaction.   At heelstrike, it has been calculated that the magnitude of the joint reaction at the foot is 5.8 times body weight for a heavy, energetically walking male. It is 2.3 times body weight for an average female walking slowly. For both male and female, the maximum joint reaction at the knee during walking is about four times body weight. The posterior cruciate ligaments carry more than twice the shearing forces carried by the anterior cruciates.

      FOOTFLAT

Inspection.   In weight bearing, the pelvis rotates on its vertical axis, the femur rotates on the pelvis, and the tibia rotates laterally on the femur.

Mechanisms.   During footflat, maximum stabilization of the foot occurs during stance when body weight is directly above the foot. Forward momentum eliminates the need for active hip and ankle flexion or extensor stabilization, but there is some knee flexion by quadricep contraction. When body weight is placed on the stance side, the plantar flexors of the foot contract to counterbalance the reactive force of the walking surface which forces the foot into dorsiflexion up to 15° at heeloff, and the adductors of the hip contract to counterbalance the pelvic adduction resulting from pelvic tilt.

      MIDSTANCE

Inspection.   At midstance, the head and trunk are vertical with the arms near the midline of the body and at an equal distance from the body. The elbows are partially flexed. On the weight-bearing side, the pelvis is rotated slightly anterior, the knee is in slight flexion, the leg is in slight lateral rotation at the hip, and the ankle is in slight dorsiflexion. There is a downward pelvic tilt on the contralateral side (Fig. 4.26).

Mechanisms.   Following full vertical weight bearing, the line of gravity moves forward on the stabilized plantar surface to produce a reactive force which contributes to ankle, knee, and hip extension. Hip extension reaches about 15° at the time of heeloff. This takes place without any active extensor muscle action, but some stabilization effect occurs by the iliopsoas. During this process, the gravity line falls anterior to the knee so that quadriceps action is no longer necessary. The ground reaction moves from the midfoot to the forefoot as toeoff approaches which increases the moment of dorsiflexion. In reaction, plantar flexion contraction peaks at heeloff to drive the body forward. While this tends to extend the knee, full extension is restricted by the gastrocnemius --an ankle and knee flexor.

Energy Absorption.   During gait, peak activity of the joints of the lower extremity is reached during the period of double support. At this period, the knee muscles are absorbing energy while the other joints are producing energy. As the hamstring group and gastrocnemius are two-joint muscles, much of this energy can be transferred to produce energy at other joints.

Compensation.   When the power output of one segment exceeds the power required, the surplus energy must be absorbed by other segments. Likewise, when the power requirement of one segment exceeds muscle output, the energy necessary must come from other segments.

Effect of Shoe Lift.   Although unsymmetrical lower extremity length has long been known to have adverse effects in the spine, only recently has its effects on contributing to depleting the body's energy stores been measured. Delacerda and Wikoff have shown that the equalization of leg length by a shoe lift equalized the time durations for the four phases of gait and decreased the kinetic energy of the lower extremity segments for both legs in spite of the difference in segmental masses of the legs bilaterally. (158)

      PUSHOFF

Inspection.   On the side of pushoff, the arm is anterior to the midline of the body and the elbow is partially flexed. On the contralateral side, the arm is posterior, the elbow is slightly extended. Both arms are equally distant from the body. On the side of pushoff, the femur is slightly rotated laterally at the hip, the knee is slightly flexed, the ankle is plantar flexed, and the toes are hyperextended at the metatarsophalangeal joint. The plantar surface of the heel and midfoot should become visible from the posterior during pushoff (Fig. 4.27).

Mechanisms.   The later part of stance occurs between heeloff and toeoff and provides the major portion of forward and vertical propulsion force. The hip adductors and iliopsoas begin to contract in anticipation of the swing phase, but most action occurs at the ankle and knee. The ankle changes from about 15° dorsiflexion at heeloff to about 35° plantar flexion at toeoff, and the extended knee flexes to about 40° as the quadriceps contract. At toeoff, the segments begin to reverse the lateral rotation attained during footflat, and this medial rotation of the pelvis, thigh, and leg continues to 20°–35°, depending on walking speed, until the next footflat is reached. Once the toes leave the ground, hip and calf muscles relax.

      ACCELERATION

Inspection.   The period of acceleration of the advancing leg occurs during the first part of the swing phase when the limb is between toeoff and midswing. The swing phase involves almost simultaneous hip flexion, knee flexion, ankle dorsiflexion, and usually a concomitant forward swing of the hip that rotates the pelvis contralaterally to some degree.

Mechanisms.   The primary forces are generated by the hip flexors and ankle dorsiflexors. Hip flexion is governed by the tensor fasciae latae, the pectineus, and the sartorius. The most powerful hip flexor, the iliopsoas, and the adductor magnus are not active during swing, according to electromyographic evaluations. Knee flexion is aided by sartorius contraction, gravity, and passive pull of the posterior hamstrings. The flexion of the knee after toeoff is passive while the thigh accelerates forward from action by the hip flexors. As the hip and knee continue to flex and the ankle dorsiflexes, the leg "shortens" so that it can clear the ground.

      MIDSWING AND DECELERATION

Inspection.   The head and trunk are vertical, and both arms are near the midline of the body and held an equal distance from the body. On the weight-bearing side, the pelvis is rotated slightly anteriorly and tilted downward, the hip and knee are flexed, the femur is rotated slightly medial at the hip, the leg is vertically aligned with the pelvis, and the foot is at a right angle to the leg and slightly everted (Fig. 4.28).

Mechanisms.   At heelstrike, the ankle is held in its neutral position by its dorsiflexors, especially the anterior crural muscles, the knee rapidly moves from flexion to full extension by hamstring contraction, and this hamstring contraction also slows hip flexion. During the swing phase, there is a ballistic movement of hip flexion where the thigh is first accelerated by the hip flexors at the beginning of swing and then decelerated by the hip extensors.

      LATERAL OBSERVATION

From the lateral note rhythm, symmetry, speed, and stride lengths of cadence. Vertical excursion is best viewed from the side. Check if the duration of the stance phase is the same bilaterally. As the patient walks, note all deviations from normal gait. Normally, the head and trunk are vertical, stride length is even, and the arms swing freely and alternate with the leg swing.

Note the foot at heelstrike and pushoff. The foot is about at a right angle to the leg and the knee is extended but not locked at heelstrike. At pushoff, the foot is firmly flexed and the toes are hyperextended. The foot easily clears the floor during the swing phase of the gait.

Displacement.   The trunk should be vertical at stance. Observe the degree of lurch during flexion, extension, and during the swing phase. Note degree of hip, knee, and ankle flexion. If the head is carried far forward, seek further evidence of atlanto-occipital fixation, subluxation, costoclavicular or neurovascular syndrome, upper dorsal lesion, or shoulder disorder. These malfunctions would also be suspect if the head were titled to one side, but lateral carriage is found more commonly in torticollis, in visual defects, and in primary or secondary scoliosis.

Pathologic Postures.   If pain is present, determine where and when it is greatest. Check for trunk fixation in flexion or extension. Fixed lordotic and kyphotic spines will be evident during both stance and swing, but posterior pelvic tilts are difficult to observe. Shoulders drooping forward may be an indication of cardiac dysfunction, lung or pleural pathology, depression, or a dorsal lesion. Diabetics and those suffering from cardiorenal disorders often have pot bellies. Due to the lack of tone in the abdominal musculature, the viscera sag downward which results in organ malposition and disturbed function contributing to the problem.

      ANTERIOR-POSTERIOR OBSERVATION

From the front and rear, note rhythm, symmetry, and speed of cadence. Lateral motions are best viewed from the front or rear. As the body advances, note smoothness of the body's vertical oscillation. Pathology may express itself in increased vertical oscillation and disrupt the normally smooth pattern. Normally, the pelvis is centrally positioned over the line of progression at toeoff and begins its movement toward the side of the weight-bearing limb.

Pelvic Displacement.   Note the degree of pelvic tilt and drop on each side. This is more easily noted by watching the top horizontal line of the underwear. A lateral shift of the pelvis and hip of about one inch to the weight-bearing side is normal to center the weight over the hip. Maximum pelvic tilt is usually reached just after midstance. Its degree is normally determined by stride width, which corresponds to the lateral shear forces acting on the pelvis, and walking speed, which determines how long these shear forces are acting on the body. Lateral shifting is accentuated in gluteus medius weakness and should be noted. A gait exhibiting bending to one side may be the result of a pericardial or pleural friction rub, a sacroiliac lesion, shoulder condition, affection of the brachial plexus, or lesion in the upper dorsal section of the spine. On the other hand, a ram-rod gait is a sign of a thoracic lesion, sacralization, or spasm of the lumbar paravertebral musculature --all of which may or not be associated with an abnormal lumbar curve. A fixed pelvic tilt or elevation will not change from stance to swing. The pelvis is normally level at heel contact, drops to its maximum on the side approaching toeoff during double-support, then returns to a level position shortly after toeoff and remains there until heel-strike. As speed increases, the degree of drop increases on the side in the swing phase.

Base Width.   Check the walking base width for broadness, stability, and consistency (Fig. 4.21, right). From heel to heel, base width is normally not more than from 2 to 4 inches. If wider, dizziness, unsteadiness from a cerebellar problem, or numbness of a foot's plantar surface may be a cause for the wider base. An abnormally decreased base usually produces a crossover "scissor" action after midswing.

Limp.   Any articular malfunction from the spine to the foot may result in a limp. Muscular weakness or spasm, fascial contraction, fracture, a torn ligament or tendon, bone disease, or a neurologic affectation may be cause for a limp. Generally, an uncomplicated limp can be traced to a knee, ankle, or foot dysfunction or deformity, a hip disorder, or a sacroiliac or lumbar lesion. A female gait exhibiting rigid buttocks is a sign of a uterus retroflexed or prolapsed, or of a lumbosacral lesion.

      DIAGNOSTIC STANCE AND SWING CLUES

Heelstrike.   Inability of a foot to heelstrike is an indication of a heel spur and associated bursitis or a blister. Failure of the knee to fully extend during heelstrike is a sign of weak quadriceps or a flexion fusion of the knee. A harsh heelstrike, usually associated with knee hyperextension, is a frequent sign of weak hamstrings.

Footflat.   When the foot slaps down sharply after heelstrike, weak dorsiflexors should be suspect.

Midstance.   Fused ankles will prevent a midstance flat foot. Weak quadriceps display themselves in excessive flexion and poor knee stability during mid-stance. A midstance forward lurch of the hip is a typical indication of a weak gluteus medius, while a midstance backward lurch is a sign of a weak gluteus maximus.

Pushoff and Swing.   If the patient must rotate the pelvis severely anterior to provide a thrust for the leg, the cause is most likely weak quadriceps. If the hip is flexed excessively to bend the knee and thus prevent the toe from scraping the floor as in a steppage gait, weak ankle dorsiflexors are the usual cause. Failure to hyperextend the foot during pushoff is a sign of arthrosis. Pushing off with the lateral side of the front of the foot is usually seen in disorders involving the great toe. A flat-footed calcaneal gait during pushoff is symptomatic of weak gastrocnemius, soleus, and flexor hallucis longis muscles. The foot will have trouble clearing the floor if the ankle dorsiflexors are weak or the knee is unable to flex properly.

      ANTALGIC GAITS

Guarded Limps.   A limp may be a sign of disease, malfunction, or both. It may also be in compensation to another condition such as a sprained ankle, injured knee, old fracture malunion or hip surgery. However, the majority of limps seen are those desribed as "guarded" limps. Guarded limps frequently point to specific musculoskeletal disorders. These limps are the result of the patient walking in a manner that protects or relieves stress upon an area that would otherwise be uncomfortable or painful. The term "antalgic position" is that static posture assumed by the patient to produce the same pain diminishing effect as does a guarded gait.

Midspinal and Bilateral Spinal Pain.   When pain is in the midline of the spine, the gait pattern is guarded, symmetrical, slow, with a short stride and restricted trunk rotation and pelvic tilt. If paraspinal muscle spasm is present, the patient will tend to lean backward throughout the gait in compensation. However, if the irritation is located at the posterior aspect of the spinal column (eg, articular facets), the patient will tend to lean forward throughout gait in an attempt to gain relief by reducing weight on the sensitive area. Walking on the toes, as if walking on eggs, is often seen in cases of lumbosacral or cervical lesions to reduce jar. To avoid jarring any sensitive joint, the heel strike is usually eliminated and the length of stride is shortened by reducing the swing phase.

Unilateral Spinal Pain.   Walking in a stooped position with one hand supporting the back is a frequent sign seen in a lumbar lesion. During both stance and swing in mild or moderate irritations, the trunk usually leans toward the affected side in compensation to muscle splinting. However, in pronounced intervertebral disc or sacroiliac lesions, the lean is usually away from the site of irritation to reduce pressure.

Hip Pain.   While the hip joint of one extremity is in the stance phase and acts as the fulcum for rotation, the other hip in the swing phase rotates about 40° forward. This normal hip rotation is not seen in patients suffering a stiff or painful hip. When a hip is painful, the gait is asymmetrical, the base is widened during swing, the stance phase is reduced on the affected side and made longer on the unaffected side, the trunk is thrown forward during stance to shift the center of mass, and the affected hip is lifted so the limb will clear the floor. The affected hip is quite fixed in flexion, abduction, and rotated laterally to reduce joint tension. As a consequence to the hip flexion, the knee and ankle flex. Keep in mind the cyclic load on the hip during gait (Fig. 4.29).

Knee Pain.   If a knee joint is effused, with or without pain, 25° flexion offers the largest capsule volume, and thus the least tension. This flexion is compensated by ankle plantar flexion and an absent heelstrike, so that the patient will walk on the toes of the affected side. This guarded gait minimizes quadriceps function and thus reduces knee compression.

Ankle Pain.   In any painful disorder of the ankle, ankle motion will be guarded and the most comfortable position will be assumed. There is little, if any, plantar flexion during footflat or heelstrike, or dorsiflexion during heel-off. This will be compensated for by an exaggerated knee flexion after heeloff and a restricted heel rise before toeoff. The patient will reduce his base and shift his trunk so that more weight falls directly over the joint during weight bearing.

Common Stance-Phase Problems.   Most stance phase problems are the result of pain and characterized by an antalgic gait wherein the patient spends as little time on the affected extremity as possible. Gait patterns vary according to the type and location of the disorder present. A shoe problem should not be overlooked, as it is one of the more common causes. Pain in a foot during midstance may be caused by corns, calluses from a fallen transverse arch, rigid pes planus, a plantar wart, bunion, subtalar arthritis, or poor-fitting shoes. Heel-strike will be eliminated, and toe walking will be seen, if a lesion is present in the heel or posterior aspect of the foot. Lesions of the forefoot such as metatarsal or phaangeal disorders are characterized by heel walking, reduced pushoff, and an exaggerated forward hip thrust and knee flexion in compensation. Sharp pain on pushoff is often caused by corns between the toes or metatarsal callosities. In longitudinal arch disorders, weight will be borne on the lateral plantar surface during weight bearing. If chronic, excessive wear on the lateral sole of the shoe will be noted.

      NEUROLOGIC GAITS

Neurologic gaits are usually the result of unilateral flexor or extensor spasticity. The clinical picture is the result of exaggerated stretch reflexes, reflex impairment of the antagonists, and poor flexor-extensor coordination. Most all spastic gaits present a slow cadence and a repetitive pattern during each cycle.

Unilateral Flexor Spasticity.   This gait is characterized by a distinct forward lurch of the trunk, a narrow base of support, a decreased stride length, and an absent heel-strike. Usually, adductor tone is normal.

Unilateral Extensor Spasticity.   A spastic gait is common in upper motor neuron diseases that have a spastic paralysis of the extensor muscles. It is a feature of spinal paralysis, lateral sclerosis, and some other forms of myelitis and anterior tract or brain damage. The upper body is flexed while the lower extremity is extended. The locomotion pattern is characterized by a short stride length, a narrow base of support, and pelvic elevation during swing so that the foot will clear the floor. The legs are firmly extended, the foot is dragged along in a shuffling manner with the toes scraping upon the ground to permit one foot to pass the other, and the pelvis is tilted slightly. There is little knee flexion during the swing phase if the quadriceps are spastic. Heelstrike is absent and the knee is hyperextended in midstance if the plantar flexors are spastic or if the ankle dorsiflexors are weak. Usually, adductor tone is normal. In some cases, the adductors contract to cause the legs to cross (scissors gait), and the knees often rub each other, as seen in Little's disease.

Mowing Gait.   In spastic hemiplegia, there is a unilateral spastic gait in which the pelvis is tilted and the leg is swung around in front of the other with the toes often scraping the ground. It is sometimes referred to as the mowing gait. The most common cause is hemiplegia due to cerebrovascular disease, but any condition that would result in an upper motor neuron lesion can produce the gait.

Proprioception Impairment.   In this gait, named an "ataxic gait" because it occurs in locomotor ataxia, the patient walks in a stooped posture with the eyes looking at the feet. The foot is raised unusually high, thrown forward with force, and brought to the ground flat-footedly with a stamp to increase sensory awareness. While in the air and before being lowered, the foot wavers as if there is a degree of uncertainty in bringing it down. The patient walks with his feet wide apart and is constantly looking at them. This is done for the purpose of supplementing the loss of proprioception. To maintain a large area of foot contact throughout weight bearing, heelstrike is usually eliminated. It is sometimes called the "tabetic gait" and characteristic of a lesion in the dorsal ganglia, dorsal roots, or posterior column of the cord --rarely in higher levels. The ataxis is increased when the eyes are closed or when the patient must walk in a darkened room. The gait is seen in tabes dorsalis, pernicious anemia, and other disorders involving proprioceptive pathways.

Basal Ganglia Dysfunction.   This gait is characteristic of paralysis agitans or Parkinson's disease. It is sometimes called a "propulsive gait" or festination (increasing speed). The hurried "sissy" tottle of parkinsonism is due to the forward tilt of the trunk in the attitude of a stoop and the attempt of the patient to maintain balance. As the center of mass is anterior to the base of support, the patient appears to be chasing his center of gravity. Almost all joint motion is restricted, as is arm swing, pelvic tilt, pelvic rotation, and knee flexion. The body and head lean far forward. The trunk, hips, knees, and ankles are flexed to some degree, and the subject walks with short, hurried, shuffling steps, which makes it appear as if he is being pushed from the rear and is about to fall. Heelstrike is absent, and the toe is dragged during the swing phase. It is difficult for such a patient with this gait to stop suddenly or to turn a corner. Thus, falls are frequent. Progression is slow at first, and then increases rapidly.

Cerebellar Dysfunction.   This gait, a sign of cerebellar ataxia, resembles the actions of an intoxicated person. The patient walks with the feet wide apart, takes short steps, and sways to and fro to such an extent that progression in a straight line is almost impossible. The gait resembles that of a person trying to walk on a rolling ship, constantly trying to maintain equilibrium with little success. The gait is found in tumor of the cerebellum and disease of the semicircular canals. Cerebellar lesions are invariably associated with vertigo. It may be indicative of long-term use of alcohol or other drugs ("Jake legs") or neurosyphilis. If the causative factor is unilateral deviation is to the involved side because of the hypotonia.

      PARALYTIC GAITS

Paralytic or paretic gaits with varying patterns are the result of spinal root lesions, brain lesions, nerve compression syndromes, peripheral mononeuritis, abnormal reflexes, and trauma. Table 4.2. shows the common gait deviations associated with specific muscle weakness.

If the quadriceps are extremely weak, locomotion is usually impossible as the knee is too unstable during stance. If knee flexion and plantar flexion are weak during swing, compensation is made by hip elevation. The two typical patterns are referred to as the "steppage gait" and the "waddling gait".

Steppage Gait.   This gait --also called the prancing, highstepping, or foot-drop gait-- is commonly found in infantile paralysis, multiple neuritis, peroneal nerve injury, and arsenic poisoning paralysis. The gait resembles that of a person walking in tall grass, hence its name. The flexor muscles of the foot are subject of a flaccid paralysis so that the toes hang downward when the foot is raised from the floor. To prevent the toes from dragging on the floor or catching upon objects, the foot is raised high and brought to the floor forcibly before the toes can drop. Thus the foot strikes the floor heel first or flat-footed. The gait is especially suspect in tertiary syphilis.

Waddling Gait.   This occurs when there is extreme muscular weakness in the thigh and hip muscles as commonly found in pseudohypertrophic muscular paralysis and muscular atrophy or dystrophy. In this gait, the shoulders are thrown back, the lower section of the spine is lordotic, the pelvis is tilted greatly, and while in this state, the leg is brought around and placed on the floor. When walking, the subject swings from side to side in a very noticeable manner, thus often referred to as the goose gait. This gait is also seen in bilateral hip dislocation. In gaits involving muscle weakness, the compensatory pattern is largely the result of the patient's attempt to alter the center of gravity relative to the base of support.

Hip Disorders.   Extension weakness, flexion weakness, or abductor weakness of the hip offer characteristic gait patterns:

1. Extension weakness.   During extension paralysis, the gait is grossly altered in weight bearing after heelstrike when the extensors normally contract. Due to the weakness, the trunk is thrown backward to maintain balance by keeping the center of gravity behind the axis of the hip.

2. Flexion weakness.   Weak hip flexors affect acceleration during swing, the pelvis is usually elevated, the trunk is thrown backward toward the unaffected side in compensation, but stance is rarely affected. The stride is usually short on the involved side.

3. Abductor weakness.   In upper motor neuron weakness of the hip abductors, the trunk is thrown toward the affected side during weight bearing. If uncompensated, the pelvis distinctly lunges laterally toward the affected side and dips on the side of swing. At midswing, hip and knee flexion is exaggerated on the unaffected side. In less severe cases, there is little sideward lunging because of trunk compensation. Use of a cane on the contralateral side of involvement also eliminates this lateral lurch.

Knee Disorders.   As with the hip, extension weakness or flexion weakness offer characteristic gait patterns:

1. Extensor weakness.   This pattern is often difficult to see. In stance, the knee is normally fully extended. The features of the weakness are most prominent after heelstrike when the quadriceps normally contract and the knee flexes. Seek signs of excessive heel lift during gait and excessive knee flexion during the swing phase. Knee extension is maintained at heelstrike and throughout stance by hip extension (eg, gluteus maximus via the iliotibial tract) and plantar flexion. This is assisted by throwing the trunk forward at heelstrike to move the center of gravity anterior to the axis of the knee. In pronounced cases, the patient will push the affected thigh backward with his hand to assist extension.

2. Flexor weakness.   Weak hamstrings allow full knee extension and inhibit deceleration as heelstrike approaches. This produces a quite hard heelstrike, often called an "overshot". Near the end of the stance phase, the knee fails to flex until pushoff. In prolonged conditions, the result is often the development of distinct knee hyperextension (genu recurvatum) that is most difficult to correct without the use of a check brace until the ligaments tighten.

Ankle Disorders.   Ankle plantar flexion weakness and dorsiflexion weakness exhibit charactersitic patterns:

1. Plantar flexion weakness.   If these muscles are weak, propulsion is inhibited because heeloff is impaired. The foot leaves the floor as a unit, the knee is fully extended, and the hip flexes at pushoff to begin the swing phase. As pushoff is controlled essentially by foot plantar flexion, triceps surae paralysis or Achilles tendon trauma will force some compensation by the gluteus maximus and posterior hamstrings.

2. Dorsiflexion weakness.   When the ankle dorsiflexors are mildly weak, it is possible to lift the foot from the floor, but during the swing phase, relaxation occurs, which causes the foot to be slapped down during flatfoot. In severe weakness, toestrike replaces heelstrike. This requires a compensatory increase in hip and knee flexion during the swing phase so that the foot clears the floor (steppage gait).

      RESTRICTED MOTION GAITS

Movement restricted within either the passive or active range of motion of the hip, knee, or ankle exhibits changes in locomotive patterns. The picture is usually attributable to soft tissue contractures and/or bony deformities (Figure 4.30). In pure anklyosis, from either bone fusion or excessive fibrosis, there is no joint motion whatever. The terminology in describing these conditions is often confusing because abduction contracture refers to adduction limitation, flexion deformity refers to extension limitation, etc.

Restricted Hip Flexion.   At heelstrike, the lumbar area is flexed to compensate for the pelvis being rotated and elevated, and a distinct backward trunk lunge is seen if the spine is not flexible. Stride length is shortened on the involved side. Pelvic elevation, hip flexion, and knee flexion become exaggerated during swing to help the involved limb to clear the floor.

Restricted Hip Extension.   The stride length is shortened on the uninvolved side, and midstance of the involved limb shows exaggerated knee flexion. When the disorder is severe, toe walking is seen, early heeloff occurs, a compensatory lumbar lordosis is produced after midstance, and the trunk is often thrown forward, especially if the spine is not flexible.

Restricted Hip Rotation.   Once this occurs, stride length is greatly diminished. The foot pivots laterally on the involved side during weight bearing, especially between flatfoot and toeoff.

Restricted Hip Abduction.   On the uninvolved side, the pelvis is elevated during swing and stance. A compensatory functional sciolosis that curves toward the involved side is common. A broad base is constantly attempted.

Restricted Hip Adduction.   During stance, the trunk is thrown toward the affected side. In contrast to restricted abduction, the base is kept small, and a scissor motion is usually made when the involved limb is in the swing phase. A compensatory functional sciolosis that curves toward the uninvolved side is common. This is necessary to maintain the center of gravity over the limb during weight bearing. Contracture is exhibited by a functional short-leg that is compensated for by exaggerated hip and knee flexion on the uninvolved side and toe walking during stance on the involved side.

Restricted Knee Flexion.   When knee flexion is limited, the pelvis must be elevated and the extremity circumducted so that the foot can avoid the ground during the swing phase. To assist this, there is usually a distinct toe stance during weight bearing on the uninvolved side.

Restricted Knee Extension.   If the knee is unable to fully extend, the stride length shortens on the involved side, and heelstrike is usually eliminated. The heel remains raised during flatfoot, propulsion is weak at pushoff, and hip and knee flexion is exaggerated on the uninvolved side during swing.

Restricted Ankle Dorsiflexion.   Heelstrike is absent, toe contact is seen throughout the stance phase, and the knee is forced into hyperextension. The propulsive force at pushoff is lessened. During swing, hip and knee flexion is exaggerated on the involved side and the affected limb is swung outward to help clear the ground.

Senile Gait.   This gait is caused by shortening and loss of elasticity of ligaments and tendons, and a stiffening of cartilage, muscle, and fascia as a result of the degenerative aging process. Steps are short, shuffling, and assumed in a stooped position if osteoporosis is present to cause a marked dorsal kyphosis. Whenever the passive range of joint motion is limited by structural changes, the compensatory pattern usually reflects an exaggerated motion at noninvolved joints.

Short-Leg Syndrome.   A difference in leg lengths increases the vertical oscillatory amplitude of the body's center of gravity. In compensation on the involved side, the pelvis drops on heelstrike and remains tipped throughout stance, heelstrike reduces in proportion to the leg deficiency, stride length is shortened, and toe walking is seen throughout the stance phase. On the side of the long limb, increased hip and knee flexion occurs during both the swing and stance phases.

      FUNCTIONALLY INHIBITED GAITS

In addition to those gaits discussed, locomotion may be restricted by various types of psychomotor disorders. The two major types are those due to hysteria or higher center apraxia.

Hysteria.   These gaits rarely have a repetitive pattern, and many movements are highly exaggerated. It is difficult to match gait signs with neurologic and musculoskeletal findings. Tremor usually appears during observed active exercise, and strength rapidly fades when passive movements are resisted by the patient. Although the motions are gross and unpredictable, falling is rare. If falling occurs, it is well protected. In some cases, the pattern is repetitive. This is the result of a "gait habit" that persists long after the cause of malfunction has been eliminated. The clinical picture is often confusing because persistent atrophy, edema, and vasomotor instability may be solely the result of disuse.

Gait Apraxia.   In this condition, motor power is present but the memory of how to use the power is lacking or diminished. Steps are small, slow, and uncertain, and the patient must be urged or assisted to initiate progress. This gait is characteristic of frontal lobe lesions or bilateral lesions of the corticospinal tract in the internal capsule, cerebral peduncles, or high brainstem. It is often seen immediately following prolonged bed confinement, but in this situation, it is quickly overcome.

      LABORATORY MENSURATION OF GAIT

The analysis of gait impairments in the office of a general practitioner is conducted almost exclusively through gross observation, inspection, muscle testing, range of motion analyses, electrodiagnosis, and, sometimes, electromyography. The research laboratory, however, offers many advantages in objectively quantifying gait patterns, functional deficits, and patient response to therapy. The data obtained by frame-by-frame motion picture of a body or cineroentgenography of a region in motion, for example, were described in Chapter 3. Other means are being developed each year.

To measure relative joint rotation of the ankle, knee, and hip, instrumentation at the Mayo Gait Laboratory includes three-dimensional electrogoniometers. Instrumented mats are used to measure step length and width, footswitches are used to record foot-floor contact sequences, piezoelectric force plates are used to measure floor-reaction forces, and two walkways are used to simulate variable ground conditions. The data obtained are then analyzed with the aid of a computer to assess patient progress under prescribed exercise and gait training regimens. (190)


Running and Jumping

The mechanics of running are similar to those of walking in several respects. Both walking and running require that:

(1)   weight be projected forward and the legs are carried alternately under the body for brief periods of support, and
(2)   the weight-bearing limb provides the propulsive action after the center of body weight has passed over it. Walking becomes a running gait at that point in acceleration when a period of nonsupport appears. During the phase of nonsupport where there is no surface friction, the body can be considered a missile.

Jumping is essentially the act of propelling the body into the air via rapid leg extension. It is usually considered in three phases: takeoff, flight, and landing. Jumping is governed by the same principles that govern missiles. Thus, the motions made during flight have little influence on direction, height, or distance. Their main purpose is to prepare the body for landing.

      BIODYNAMICS

During running, angular knee flexion displacement increases to reduce the effective radius of the limb as the hip of the recovery thigh begins to flex (Fig. 4.31). This decreases the limb's moment of inertia to allow a faster recovery on the swing-through with less effort. The flexing hip transfers angular momentum to the leg and foot as the limb continues to swing forward. The knee continues to extend until the foot reaches its most anterior position. At foot-strike, the body's center of mass is carried over the weight-bearing foot by combined hip extension and the forward momentum of the body. Arm swing, trunk rotation, and position and forces of the contralateral limb help to counteract the undesirable moments established during footstrike.

Running speed is essentially limited by:

(1)   the forces necessary to accelerate and then decelerate the recovery limb, and
(2)   the inertia of the lower limbs during recovery. Other contributing factors include poor strength or endurance, excessive arm or lower-extremity antagnostic muscle tension, excessive leg weight, short leg length, decreased flexibility, poor timing and coordination, slow reaction speed, and inhibited pace or motivation.

The muscle contractions occurring near the extreme of movement initiate a mechanical impulse to the limb segments that cause the limb to decelerate and reverse direction. This, in turn, gives the limb sufficient momentum to swing through its range of motion without the assistance of muscular action. It should be noted that hamstring injury usually occurs when this muscle group is attempting to reduce the speed of the extending knee.

The foot changes velocity in short periods as it accelerates and decelerates. Powerful hip and knee extension occur during the running cycle, and the gastrocnemius and soleus contract strongly before the foot strikes the ground. This prevents heelstrike by transferring body weight to the ball of the foot which subjects the arch to enormous forces when the impact force of footstrike is added to body weight. The same is true during pushoff. These forces must be absorbed by the body through the joints.

      ARM SWING

While it was once thought that the arms simply act as pendulums during gait, it has recently been established that they play an active integrated part in locomotion. The angular momentum of the arms helps to counteract the rapid changes in the angular momentum of the trunk. When walking increases to running, the elbows remain flexed and the amplitude of arm swing is increased to compensate for the necessary angular momentum of the arm.


Practical Fluid Mechanics and Buoyancy

The human body commonly moves through the fluid media of air and water. Air resistance has little effect in normal activities at slow speeds. However, in such activities as distance runs at maximum speed, skiing, kite gliding, and sky diving, air resistance and force interactions are factors to be considered.

While man is essentially a land animal, many human characteristics are useful in aquatic activity. Mechanical forces increase as the density of the fluid medium increases. For example, the force of fluid friction is readily exhibited in the energy consumed when one tries to walk or run within waist-deep water.

      BUOYANCY

A person's specific gravity is usually slightly less than water when the lungs are inflated. The buoyancy force on a body submerged wholly or partially in water is equal to the weight of the volume of water displaced (Archimedes principle).

The Center of Buoyancy.   The center of buoyancy is the center of gravity of the volume of fluid displaced prior to displacement. This volume of displaced fluid is the same shape as the submerged body. In biomechanical problems, buoyancy force is considered to act at the body's center of buoyancy just as gravitational force is considered to act at the body's center of gravity. However, these lines will not coinicide because the body is not of uniform density. Once emerged partially or wholly in water, the body's center of buoyancy is in the center of the region that displaces the most water. Thus, for a swimmer, it is in the center of the torso (lower thorax).

      EQUILIBRIUM

Static Equilibrium in Water.   When the relaxed body attempts to float within water, the swimmer's body rotates until his center of buoyancy and center of gravity are in the same plane, whether it be horizontal, diagonal, or vertical (Fig. 4.32).

Dynamic Equilibrium in Water.   Dynamic equilibrium is not difficult to maintain as long as the swimmer stays in a relatively horizontal position. The higher the body position is in the water, the lesser is the resistance. The lower the body position is, the greater is the energy economy.

Drag.   Two other biomechanical forces that affect performance are form drag and surface drag. Form drag depends on the cross-sectional area of the body that is perpendicular to the direction of water flow and the smoothness (waviness) of the water surface. Surface drag is the resistance generated between the surface of the body and the water adjacent to it, and its end result depends upon the surface area of the body, the body's velocity, and the properties of the fluid medium.

Normal posture is that posture which best suits an individual according to his or her internal and external environmental conditions. An erect posture reflects self-confidence, a readiness to act, and shows the physique to a better advantage. Clothes are designed for such a posture.

A relaxed or slouched posture usually connotes laziness, incompetence, and an inferior self-image. However, this is not always the case. That is, superior energy potential and intellectual capacity is often housed in a body that is habitually slouched. Some individuals assume habitual postures of great relaxation during periods of non-activity. This is because one will assume an energy-conserving posture during a state of fatigue.

There is no clear symptomatic picture of balance defects because individuals vary so much in response to mechanical insult. Some people present immediate symptoms upon slight deviation, while others offer no symptoms until pathologic changes are in progress. Much of this is determined by how the body is used; eg, occupational and athletic considerations.


Effects of Bipedism

Bipedism requires certain anatomic considerations to appreciate the fact that the spine and pelvis are of commanding clinical importance because of their intimate involvement with the nervous system. In the human biped, there is a unique relationship between the musculoskeletal mechanism and the neurologic bed. The neurologic factors that relate to bipedism represent the rationale of clinical chiropractic that is often readily portrayed during dynamic postures.

Derangements in the musculoskeletal system in the human are much more common than in the quadriped. Consequently, the human biped is heir to those elements that are the consequence of disturbed body mechanics. For example, the sacroiliac articulations at the time of birth are amphiarthrodial. But as standing and locomotion are acquired, the joints are induced to assume diarthrodial movements and come to possess encompassing ligaments, articulating cartilages, and a bed of proprioceptors.

      EFFECTS OF BIPEDAL STRESS

The human torso is much like a "skyscraper" wherein strain and stress is greater at certain points than at others (Fig. 4.33). Within the zone of these points of primary function and stress, there is a relatively heavy deposition of sensory nerve endings and motor end plates. When these areas, heavily populated with neuronal and vascular ramifications, are subject to trauma, occupational stress, the strains of postural fatigue, and abnormal viscerospinal reflexes, the process of transudation, fibrin precipitation, and adhesion formation ensues to establish an intramuscular and myofascial plane trigger point. To this must be added the principle of neurologic fascilitation and spread. Not uncommonly, there is a musculoskeletal syndrome complex that challenges the clinical capacity of the most healthy.

Bipedism augments the concern of gravity and weight bearing, postural faults, strains and stresses of occupation, play, and trauma. Because of such stress, the articular, syndesmotic, and myologic proprioceptive complex is often disturbed which results in the development of many common spinosomatic and spinovisceral syndromes. The intervertebral disc, especially in certain areas of the spine, becomes a most vulnerable unit of disturbance, discogenic extension, and resultant disc syndromes. A deranged spinal or pelvic segment within its motor bed will always result in disturbance of the proprioceptive bed with facilitation of the discomfort and pain phenomenon.

Functional tension (whether it be of emotional, infectious, traumatic, or immobilization origin) leads to irritation and pain. Pain leads to muscle tension, edema, inflammation, a fibrotic reaction, and ultimately to functional disability (Figure 4.34). When a muscle is under constant tension, the retained metabolites from stasis and internal tissue ischemia create a vicious cycle enhancing further tension and inflammation.


Body Type and Balance Defects

Balance defects tend to differ somewhat in the classic body types. They are especially difficult to differentiate during youth (Fig. 4.35).

      THE ECTOMORPH

In the lean ectomorph, the anatomic design has a tendency to encourage poor body mechanics. Postural relaxation is the rule unless the person has had specialized training or makes a conscious effort. Habitual relaxation leads to a forward head carriage, flat chest, and narrow subcostal angle. The ribs and diaphragm are low, and the vital capacity is decreased. The abdomen is small above and protrudes just above the symphysis pubis, while retroperitoneal fat is slight. Visceroptosis is usually evident. The spine presents sharp bends in the midcervical and upper dorsal areas. There is a sharp lumbosacral curve with some accompanying lordosis. The pelvis inclines more than 60°, and the knees are often hyperextended.

      THE ENDOMORPH

Such extremes of relaxation do not usually occur in the stocky endomorph because the anatomic construction is not so favorable to strain. However, the endomorph's shorter ligaments and restricted range of joint motion allow symptoms to appear with only moderate deviations from the ideal. It is common to see sagging of the large, heavy viscera in the poorly conditioned individual, compensated for by a backward inclination of the trunk. Because of the limited range of spinal motion, bending to maintain the center of gravity over the feet usually comes either at the hips or dorsolumbar junction. Thus, both areas are common points of stress and fatigue.

      THE MESOMORPH

Faulty body mechanics also occur in the intermediate body type, resembling either an overly relaxed ectomorph or endomorph, and thus are difficult to profile.

      BIOMECHANICAL PROPERTIES OF DIFFERENT BODY TYPES

By using a mathematical model to estimate the size and inertial properties of the segments and the body as a whole of three boys, Jensen has shown that varying biomechanical properties have important implications in the development of motor skills and efficiency of children of different body types. (222)

Comparisons were made between an endomorph and ectomorph who had similar link dimensions and between the endomorph and mesomorph who had a similar body mass. For the endomorph, some of the segment masses were substantially greater than would be expected by comparing the total body masses of the endomorph and ectomorph, suggesting significant constraints on the development of upper and lower extremity linear momentum. These differences were even more pronounced when the segmental and whole body principal moments of inertia were compared, and the greatest differences were for the longitudinal axes. When comparing the inertial properties of the endomorph and mesomorph, it was found that they were similar. The mesomorph in this study, however, was older and developed physically to a greater extent than the endomorph -- thus more able to accommodate to the contraints.


Etiology of Postural Faults

From a physiologic standpoint, "normal" posture is that condition in which the body functions the most efficiently. From a structural standpoint, a population's normal posture is more difficult to judge. That shown in most illustrations are of "ideal" posture, not normal posture. Posture is constantly shifting to rest active muscles and to adapt to various conditions such as ground surface, heat and cold, sickness and health, sadness and joy, clothing, and social customs.

A few influences on human posture are:

(1)   gravity;
(2)   environment, eg, occupation, weather;
(3)   architecture of the vertebral column, upper and lower appendages, organs and tissues that attach to or are suspended from the spinal column;
(4)   physiology, normal and abnormal,
(5)   pathology,
(6)   emotional states; and
(7)   pain.

Subluxations are often the forerunners of balance defects brought about through the effort of the spinal column to compensate for the stress and thus to reduce the more serious effects. Balance defects may also originate from habitual faulty postures in standing, sitting, and lying, as well as from activities which constantly employ the forces of the large muscles in asymmetrical action. When created, such defects serve to lessen the power of the body to withstand shock and are, in turn, the precursors to subluxations.

Other causes of defects in balance are found in the frequent occurrence of unequal lower extremities, in faulty development of vertebrae and the sacrum, and from the effects of abnormal reflexes. The least common causes of balance defects can be attributed to inheritance and disease. Constitutional stress, visceral malfunction, nutritional status, fatigue and debility, neuromuscular tension, a large variety of psychologic factors, height, weight, and body type all combine to express themselves in one's posture, body balance, and motor ability.


Basic Physiologic Reactions to Postural Faults

No two individuals react in an identical manner to actual or potential loss of body balance. All vary somewhat in the accommodation process depending upon one's gross structure and functional capabilities, the momentary potential for redistributing body mass, and the visual efficiency necessary to guide correct accommodations.

Most balance faults witnessed in practice will be within "physiologic" limits without obvious structural deformity, yet it should be appreciated that abnormal function leads to reduced performance capabilities early and to pathology later if left uncorrected. Isolated muscle weakness should be suspected especially in situations of head or pelvic tilt, trunk imbalance, scoliosis, and uneven gait or limp.

      BASIC FACTORS

Tolerance.   Poor posture from habit, disease, or abnormal reflexes results in constant structural malalignment which allows a disproportionate amount of weight and muscle pull to fall upon some parts. This alters the normal locomotion apparatus and functions of the internal organs as well. While these changes may develop insidiously, the resulting static abnormalities produce pathologic changes in the body during standing, sitting, lying, and motion. Such abnormalities are tolerated for a short time, but sooner or later, serious, and often subtle, maladjustments result when the body's compensation resources become exhausted. These factors, in total, may predispose an individual to injury or hinder performance.

Endurance.   An important factor in health care is that, with good postural body mechanics, balance is maintained with the least amount of muscular effort, thus encouraging longer endurance, with less strain on any one part. Locomotion can be made without wasted time or energy. Muscle pull in maintaining an erect carriage is more direct, thus avoiding strain. A natural balance is maintained between the iliopsoas group and the hip extensors, and a similiar condition exists at the knee and ankle joints.

Effort.   Energy requirements vary considerably with different postures. The rigid "military" posture requires about 20% more energy than the relaxed standing posture. In this rigid posture, blood pressure rises because of the muscular effort required. A completely relaxed standing position requires little more energy than that required for the sitting position.

Regional Effects.   Postural faults can lead to a number of regional disorders. For example, a round-shouldered posture alters the glenohumeral articulating mechanism by depressing the overhanging acromion in front and rotating the dependent arm internally. Both of these conditions encourage cuff entrapment and attrition. Exaggerated cervical or lumbar lordosis decreases the size of the intervertebral foramina, frequently resulting in chronic radiculitis and degenerative changes. An exaggerated thoracic kyphosis decreases rib excursion and alters the functional motion of the shoulder girdle. These and many other postural disorders will be discussed further in future chapters.

      FUNCTIONAL STRESS AND FATIGUE

In chronic balance defects, physiologic stress and fatigue cannot be discussed in unrelated terms. Stress arises when the body is forced to be used in a position that is not favorable to muscle balance or when the joints are at their physiologic limit of articulation. Thus, pull comes from ligaments rather than muscles. The result is tissue insult leading to edema, pain, and physical deformity that is referred to (l) the structures upon which the strain is imposed, or (2) the cutaneous branches of the spinal nerve root supplying the strained tissues. Long-term muscle strain results in adaptive changes occurring in the joints and ligaments to meet the needs of the malaligment. Thus, low-key chronic sprain is a part of the picture. Abnormal fatigue is the result of wasted energy.

In the spine, for example, the more pronounced an abnormal curvature, the greater becomes the mechanical disadvantage to which the supporting structures are subjected. Thus, the process is a vicious cycle. Along with chronic stress and fatigue, constant pull causes small tears in ligamentous attachments. This results in a series of subperiosteal hemorrhages which later may calcify into exostoses, becoming extremely painful upon further stress. Such a situation may occur in any joint that is subjected to prolonged strain, but it is especially common in the spine and other weight-bearing joints.

      NEURALGIA

In spinal imbalance, there always appears to be some degree of intervertebral foramina insult present. Neuralgic pains in the thorax and legs are common. Less common, because it mimics viscera disease, is intercostal neuralgia. If originating in the cervical region and associated with hypertrophic changes, pain is often referred about the shoulders and down the arms, frequently being mistaken for angina pectoris. Similar neuralgic pains in the chest walls can be mistaken for pleurisy, pleural adhesions, or pulmonary lesions. Auscultation will serve in the differentiation.

      INTRAFASICULAR ADHESIONS

A muscle in spasm or under strain from any cause (or a stressed tendon or ligament) will become congested. This congestion always results in some degree of transudation and the conversion of fibrinogen into fibrin, which acts as a cobweb-like adhesion or interfascicular gluing that impedes fascicular glide. As a result in muscles, tendons, and ligaments under strain, painful interfascicular constrictions occur, leading to the common algias of these structures.

If permitted to continue, collagenic infiltration and even calcific deposition may take place. When a tendon is likewise involved or when a ligament is subject to strain, similar changes take place with an invasion process resulting in possible fibrosis and calcific tendonitis or syndesmitis.

      TRIGGER POINTS

Concurrently, similar events occur in the myofascial planes at a point of major tensile stress leading to the development of "trigger points" and the resulting delta or spread effect. All muscles have their fascial encasements (epimesium, perimesium, endomesium); and, as muscles lie and move one upon the other, the myofacial planes are described. The amount of fasciculi involved in the all-or-none contraction effort determines the tone or strength of muscle contraction. Furthermore, a muscle usually does more work at one point of its composite than at another.

      CIRCULATORY IMPLICATIONS

Circulatory disturbances are rarely absent in gross postural faults. The low diaphragm results in venous congestion in its failure to assist blood returning to the heart. Sagging viscera stretch mesenteric vessels and narrow their lumina. Thus, circulatory symptoms may manifest throughout the body. For instance, medical researchers have recorded the relief of eyestrain and mild myopia in children by postural correction alone. They explain this as a relief of venous congestion in the head.

In extreme cases, impaired circulatory inefficiency may be sufficient to produce a marked fall in blood pressure and loss of consciousness. This is said to be the result of general muscle relaxation with pooling of blood in the venous reservoirs, especially in the abdomen, thus reducing the practical blood volume. More often it causes only dyspnea and weakness, sometimes accompanied by palpitation. Precordial pain resembling angina pectoris is not rare.

      DRAINAGE IMPAIRMENTS

Faulty posture mechanics may cause the liver to rotate anteriorly and to the right. Traction is thereby exerted on the common duct and in some cases seriously interferes with biliary drainage. Ptosis of the kidneys, especially the left kidney, results in traction on the renal veins which may obstruct venous outflow to cause passive congestion and albuminuria.

      VISCERAL IMPLICATIONS

It is unwise to consider the various parts of the body as separate entities. All parts share responsibility in the orthograde posture. Any disturbance in one part causes an immediate and definite functional change in other parts.

Extreme curvature and malalignment produce physiologic changes and are considered to be pathologic, but how much deviation is possible without causing severe impairment of health? The effect on function varies among research literature. Most all agree, however, that poor body mechanics predisposes to certain visceral disorders; ie, the viscera are held in their optimum position for function in good body mechanics. If mechanics are good, the abdominal cavity is shaped like an inverted pear with adequate space above L4 for the abdominal viscera of an intermediate body type.

Nature provides good support for the abdominal organs when the body is normally erect. In the ideal attitude, tissue ledges and shelves exist which partially support the abdominal organs. However, if the lumbar and dorsal curves increase and the abdominal wall relaxes, these vital supports are lost.

The Stomach.   With the stomach lying mainly to the left of the spine and supported by a diaphragmatic attachment behind the transverse sagittal plane, there is little tendency for downward displacement if there is no rib cage deformity or abdominal muscle weakness.

The Liver.   The liver is generally posterior to the transverse sagittal plane. It is partly supported by the surrounding organs and its attachments to the diaphragm, but most of its weight is borne by the concave space at the side of the spine and by the curves of the lower ribs.

The Spleen and Pancreas.   The spleen is well back and held in place by peritoneal folds, and the pancreas depends chiefly on the surrounding organs for support.

The Kidneys.   The kidneys normally rest in definite depressions which begin around the level of L4 and are supported by the psoas muscle, quadratus lumborum, and retroperitoneal fat.

The Colon.   The attachments of the hepatic and splenic flexures of the colon are external to the kidney and attached to the posterior surface of the abdominal cavity. About 87% of the weight of the abdominal organs is borne by the psoas shelf and the muscles of the abdominal wall.

Digestive Disturbances.   Mild digestive symptoms may be present in the apparently healthy person. This is sometimes traced to a degree of visceroptosis which results in dysfunction of the displaced organs. Abdominal dilatation and motility disturbances are not infrequent occurrences. This is most likely the outcome of stretching of the sympathetic nerves. Pottenger points out that stretched nerves within involuntary or voluntary muscles usually produce a temporary paralysis. In addition, when the abdominal cavity becomes shortened longitudinally, the viscera become crowded as do the glands of internal secretion and the nerve ganglia as well. Thus, orthostatic albuminuria, dysmenorrhea, and constipation may sometimes be associated.

Effects of Prolapse.   As a result of visceroptosis, a compensating lumbar lordosis, and the insult at the intervertebral foramina, symptoms can be diffuse and subtle. Duodenal stasis may be attributed to increased tension on the superior mesenteric vessels. One study has shown that postural correction relieved 65% of cases exhibiting a picture of duodenal obstruction; and 75% of cases presenting gastric distress, nausea, and abdominal pain associated with visceroptosis. Narrowing of the IVF may cause severe pain that has a segmental distribution and evidenced in the skin, muscle, or parietal peritoneum. This condition is usually misleading as to origin as it suggests the presence of some intra-abdominal disorder.

      RESPIRATORY CONSIDERATIONS

Most all physical activities require good lung capacity, and respiratory balance and the maintenance of proper intra-abdominal pressure are dependent upon good body mechanics.

The Diaphragm.   In the ideal physical attitude, the position of the head well poised and the chest held high is important because the anterior mediastinal ligaments attached to the diaphragm originate in the deep cervical fascia and are attached to the lower cervical vertebrae. When mechanics are poor, a lowered diaphragm is the rule, and proper coordination of the muscles of respiration is lost. This abnormal position may decrease vital capacity by more than half. Venous and lymphatic return is greatly assisted by the rhythmic contractions of the diaphragm. When the diaphragm has been lowered, it has a much shorter range of excursion and is thus much less effective as a circulatory aid.

Respiratory Efficiency.   Because only a small part of available lung tissue is ample for the minimal requirement of gaseous exchange in the relaxed state, respiratory efficiency is difficult to measure during the nonactive state. The small gain in maximal diaphragmatic excursion and vital capacity resulting from postural changes can be considered inconsequential. Thus, the physiologic efficiency in the erect posture, relaxed or rigid, should not be considered "normal" because the efficiency of the metabolic and circulatory systems is reduced.

      POSTURAL INSTABILITY: PRECURSOR TO LOW BACK PAIN

Porterfield feels that most low-back stains and sprains originate in tissues that have been chronically stressed by poor posture. He states that many patients have decreased overall fitness, asymmetrical skeletal forces, and an unstable lumbopelvic region that is highly vulnerable to injury, and thus are "accidents waiting to happen." If normal function and postural biomechanics are not restored, frequent reinjury and chronic symptoms often occur. (245)

It is Micheli's opinion that much of the postural instability that leads to low back pain in adolescents represents a transient overgrowth syndrome where, during the second growth spurt, the bony elements develop faster than the ligaments, tendons, and strong dorsal fascia. The result is a combination of taut weak abdominal muscles anteriorly and lumbosacral fascia and hamstrings posteriorly, which produces a posterior decompensation of the trunk over the pelvis. The typical compensation mechanism for this structural imbalance is to develop a mild round back, which helps to rebalance the trunk more anteriorly over the pelvis, and this can lead to wedged vertebral bodies at the apex of the compensatory thoracic kyphosis. (246)

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