Clinical biomechanics_ Body Alignment, Posture, And Gait

CHAPTER 4: BODY ALIGNMENT, POSTURE, AND GAIT

http://www.chiro.org/ACAPress/Body_Alignment.html[18/10/2014 04:49:04]

CHAPTER 4:BODY ALIGNMENT, POSTURE, AND GAIT

This is Chapter 4 from R. C. Schafer, DC, PhD, FICC's best-selling book:Clinical Biomechanics: Musculoskeletal Actions and Reactions

Second Edition ~ Wiliams & Wilkins

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Gravitational Effects Posture Analysis Postural Changes During Growth Gravitational Forces Stabilization Mechanisms The Alexander Technique The Perry Technique Stance and Motion Postures Static Stance and Sitting Postures Dynamic Postures The Walking Function Examination of Gait Running and Jumping Practical Fluid MechanicsTypical Effects of Balance Defects Effects of Bipedism Body Type and Balance Defects Etiology of Postural Faults Basic Physiologic Reactions to Postural Faults

Chapter 4: Body Alignment, Posture, and Gait

With the background material offered in the basic principles of the musculoskeletal system, statics,dynamics, and joint stability, this chapter discusses how these factors are exhibited in body alignment andposture during static and dynamic positions.

Gravitational Effects

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 bebased upon mechanical principles. In the absence of gross pathology, postural alignment is a homeostaticmechanism that can be voluntarily controlled to a significant extent by osseous adjustments, direct andreflex muscle techniques, support when advisable, therapeutic exercise, and kinesthetic training.

In the health sciences, body mechanics has often been separated from the physical examination. Becausephysicians have been poorly educated in biomechanics, most work that has been accomplished is to thecredit of physical educators and a few biophysicists. Prior to recent decades, much of this had been metwith 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 thatspinal distortions result in the development of subluxation syndromes. Consequently, an array of differentmethods and instrumentation has been developed for this type of analytical approach such as plumb lineswith 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 theinterpretation of findings. Regardless, recorded analyses of body alignment serve as a guide to a patient'sholistic attitude, structural balance or imbalance, hypertonicity, need for therapeutic exercises, habitualstance, 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 torealize that the examiner's peripheral vision is used for judging the body bilaterally. This is true in postureanalysis as well as in the physical examination when, for instance, bilateral motion of the rib cage isassessed. If the examiner has a dominant eye, the reclining patient should be observed with the dominanteye 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 levelof 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, theright 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 nottry to assume "good posture" or the "militarystance". Note body type and then the followingcheckpoints relative to a lateral plumb line fallingjust anterior to the external malleolus (See Figure4.1) and an anterior or posterior vertical linebisecting the heels.

Head and Neck. From the side, forward orbackward shifting of body weight (not normalsway) can be judged by the position of theline from the ear. From the rear, note theposition of the patient's head by comparativeear level. If the head is tilted to the right, thechin will tilt to the left. Note the bilateraldevelopment of the sternocleidomastoideusand suboccipital muscles. Asymmetricalfullness of the suboccipital musculatureindicates upper cervical rotation.

Shoulder Girdle. From the side, note theprominence, rotation, or tilting of the inferiorangles of the scapulae. From the rear,observe the comparative height of thescapulae, comparing one to the other. Thecervicobrachial spine is always scoliotictoward the side of the high shoulder. Checkfor winged scapulae or for scapulae failing tolie smoothly on the chest wall. Note thedistance of the scapulae vertebral bordersfrom the spine. The midthoracic spine isalways scoliotic toward the side on which thevertebral 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 scoliotictoward the right. If the shoulder is high on the right yet the left scapula flares, the cervicobrachialspine 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, orpathologic signs such as Harrison's groove, funnel chest, barrel chest, or pigeon chest. From therear, note the contours of the trapezius muscles for normal development or for abnormaltightness or tenderness. Note the angles of the ribs. A difference in the height of the scapulae andthe iliac crests usually indicates a scoliosis. Lateral positions of the spinous processes andanterior or posterior positions of the transverse processes together with an elevation of the anglesof the ribs indicates a rotation of vertebrae.

Abdomen. From the side, check the degree of abdominal muscle relaxation. Keep in mind thatchildren normally have a prominent abdomen and adult women have a deposit of superficial fatlying 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, comparethe line of the spinous processes. Bear in mind the possibility of a spinous process beingasymmetrical, 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 theheight and depth of the body angle as observed from the posterior. A low and less prominent iliaccrest will be best observed from the front. Note the comparative height of the iliac crests andgreater trochanters. Check the comparative height and depth of the sacral dimples, the positionof the gluteal cleft, and the bilateral buttock height. If chronic sciatic neuralgia is on the high iliaccrest side, degenerative disc weakening with posterolateral protrusion should be suspected. If itoccurs on the side of the low iliac crest, one must consider the possibility of a sacroiliac slip andlumbosacral torsion as being the causative factor.

Legs. From the side, note the degree of knee hyperextension. From the front, check for anydegree of genu valgum or genu varum by the space between the knees. Seek possible tibialtorsion 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. Fromthe front, check for flattening of the longitudinal arch by noting the position of the naviculartubercles. 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 limitedduring the second half of prenatal life, the uterine walls act as restricting barriers to fetal extension. Toadapt, the fetus adopts a position of flexion for maximum comfort. This results in a gently kyphotic spinalcurve which extends from the atlas to the sacrum (Fig. 4.2).

Table 4.1. Developmental Progress

Skill Average Age

Head up, prone 3.2 mo.

Puts hands together 3.7 mo.

Grasps small objects 4.1 mo.

Sits, head steady 4.2 mo.

Arm support 4.3 mo.

Rolls over 4.7 mo.

Reaches for objects 5.0 mo.

Bears some weight on legs 6.3 mo.



Accepts objects in hands 7.5 mo.

Pulls to sitting position 7.7 mo.

Sits without support 7.8 mo.

Resists toy pull 10.0 mo.

Pulls to standing position 10.1 mo.

Thumb-finger grasp 10.6 mo.

Stands briefly, no support 13.0 mo.

Walks forward 13.3 mo.

Kicks ball 2.0 yr.

Throws ball 2.6 yr.

Rides tricycle 3.0 yr.

Hops on one foot 4.9 yr.

Catches ball 5.5 yr.

This list shows selected normal motor skills at average ages from 3-65 months.

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 inthe extremities in the horizontal position. The first attempt to defy gravity occurs when the baby tries toraise 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 (Table4.1). The ability to roll from prone to supine is usually established by 5 months, and from supine to proneat 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 lordosisbegins 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. Forstability, he stands and walks with a wide stance to widen the base of support. This is enhanced bydiapers, which increase the distance between the upper thighs. During early totter when walking isunsteady, the child leans forward to help forward progression, the legs are partly flexed, and the arms areabducted 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 erectposition. At this age, the legs will be held closer together, but there will still be a degree of flatfootedness, aprominent 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 abdomenbecomes less prominent, and the foot develops a longitudinal arch. Height increases steadily, but at aconstant rate. During the early years of school, the child's posture is one of extreme mobility. The kneesmay show distinct hyperextension in standing, the pelvis is tilted downward and forward 3040, theabdomen protrudes, the lumbar area is usually lordotic, but may lean back sharply from the lumbosacralarea, the scapulae are braced back by the trapezius muscles, often winged, the dorsal area is mildlykyphotic, and the buttocks protrude. A mild "sway-back" condition during this developmental stage shouldnot 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. Withoutassistance, such a child will travel as a quadriped, coordinating his or her four limbs so that three limbs areon the floor at the same time to offer the stability of a tripod. Thus, walking upright can be considered atrial-and-error translational learning process. This translation is the product of measurable angulardisplacements 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 toimprove 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 thesame at puberty. The trunk continues to grow after the extremities slow their rate of growth in thepostpuberty period. This changes the ratio of sitting to standing height. Sitting height is about 70% of totalheight at birth and about 52% for 16-year-old girls and 14-year-old boys. Thus, postural adjustments mustbe 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 pelvictilt decreases to 2030. The knees are slightly bent, but the earlier hyperextension is not necessary tobalance 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 neckprojected 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 profoundinfluence on his or her quality of health and performance. While gravity stabilizes the lower extremities instanding and provides friction for locomotion, it also places considerable stress on those body partsresponsible for maintaining the upright position. Without appropriate neuromusculoskeletal compensationand accommodation, such actions result in imbalance and often falling. Thus, postural deviations resultingin 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 pointwhere the gravitational pull on one side of the body is equal to the pull on the other side. This point is thebody's center of gravity, and it constitutes the exact center of body mass (Fig. 4.5). When the center ofgravity is above the base of support and the pull of gravity is successfully resisted by the supportingmembers, 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 thesecond sacral segment; ie, about 55% of the distance for women and 57% for men, from the plantarsurfaces to the apex of the head in the erect position. Its location will vary somewhat according to bodytype, age, and sex, and move upward, downward, or sideward in accordance with normal positionmovements and abnormal neuromusculoskeletal disorders.

The accumulation of fat and the loss of soft tissue tone are common factors in altering one's center ofgravity. Thus, the center of gravity shifts with each change in body alignment, and the amount of weightborne 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 erectmodel subject, falls from above downward through the earlobe, slightly posterior to the mastoidprocess, through the odontoid process, through the middle of the shoulder joint, touches themidpoint of the anterior borders of T2 and T12, then falls just slightly anterior to S2, slightlybehind 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, thelateral line of gravity passes through the occipital protuberance, the C7 and L5 spinousprocesses, the coccyx and pubic cartilage, and bisects the knees and ankles. Thus, the A-P andlateral 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 visualcomparison to the line of gravity. For example, when the plumb line is centered over S1, it shouldfall in line with the occipital protuberance. In uncompensated scoliosis, however, it will be seen tofall lateral to the occipital protuberance.



Weight Bearing. The most economical use of energy in the standing position is when thevertical line of gravity falls through a column of supporting bones. If the weight-bearing bonysegments are aligned so that the gravity line passes directly through the center of each joint, theleast stress is placed upon the adjacent ligaments and muscles. This is the ideal situation, but itis impossible in the human body because the centers of segmental links and the movementcenters 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 thestability of its individual segments. The force of gravity acting upon each segment must beindividually neutralized if the body as a whole is to be in complete gravitational balance. Thatpart 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 ownpartial center of gravity and partial gravity line.

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

BODY BALANCE AND EQUILIBRIUM

Active and Passive States. Positions of the body that require muscular forces to maintainbalance are said to be in active equilibrium, while those that do not require muscular effort are inpassive equilibrium. In passive equilibrium, all segmental centers of gravity and the centers of alljoints fall within the gravity line of the body which must fall within the base of support. Thisrequires complete neutralization of all linear and rotary components of gravitational force by jointsurfaces and the base of support. Thus, such a state is impossible in the erect position butpossible in the horizontal position.

Balance. When the forces of gravity on a body are in a balanced position, the pull is equal on allsides about the center of gravity; ie, its center of gravity is directly above its base of support andthe body is quite stable (Fig. 4.7). The amount of body mass outside this base does not affect theequilibrium unless the center of gravity of the mass is altered. If a part is laterally shifted to oneside without a compensatory shift of another part of equal weight, the center of gravity isdisplaced sideward. The body will topple if the center of gravity is displaced outside its base ofsupport because gravity pulls greater on the side of weight displacement. Because malesgenerally have a larger thorax, broader shoulders, and heavier arms than females, they aretoppled 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 notcoincide with the common line of gravity. In fact, many partial centers are quite distant from thecommon line, and this causes active rotary torques in many joints because of gravitational pullwhich must be neutralized by antigravity muscles. A weight-bearing joint is considered to be inequilibrium if the gravity line of the supported structure is equal to the joint's axis of rotation. Ifthe gravity line is posterior to the joint's axis of rotation, the superior segment tends to rotateposteriorly in compensation. If it is anterior to the axis, the superior segment tends to rotateanteriorly.

Toppling Rate. The rate of movement of an unbalanced body which is toppling depends on theamount of lateral displacement of the center of gravity from its base of support. For this reason, atoppled tree falls slowly at first because of trunk resistance and then rapidly as its center ofgravity 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 itsbase 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 downwarddirection with the part's mass acting as if it were at its center of mass (Fig. 4.8). The effectiveness of thisweight for rotating a part can be changed by shifting its position in relation to the fulcrum, because thefarther the gravity line falling through the center of mass is from the axis of motion, the longer will be themoment 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 jointsimply by changing the part's position. For example, it is easier to raise a flexed leg in the horizontalposition than a straight leg. This flexion does not change the limb's weight. The straight knee increases themoment of the gravitational force because the distance from the action line of the gravitational force on thehip has been shortened. For the same reason, it is much easier to do situps with the hands at the sidesthan when the hands are extended overhead.

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

Stabilization Mechanisms

Electromyograph studies have shown that very little muscle activity is required in the normal relaxedstanding position. Most action involves those muscles that act around the ankle. The minimal activitynecessary is attributed to the elastic properties of muscle, joint locking, and the tension from the passivestretch 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 andhip joints are fully extended during weight bearing, and the knee joint "screws home" by slightly rotating onthe 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 ofmass above its base. For example, a book laid flat upon a table is difficult to upset as compared to onestanding 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 oftoe position in the standing position, stability is provided if the gravity line falls approximately midwayalong the base of support. That is, the body is stable until the center of gravity falls perpendicularly outsidethe base of support. The larger the base of support, the greater displacement of the center of gravity from amidpoint before balance is lost. The use of a cane or crutches increases stability because they provide anincreased base of support.

Stance and Stability. The erect body is a poorly engineered model from a strict biomechanicalviewpoint because the heavier portions are placed upon a narrow base of support, similar to aninverted 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 achiropractor 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 theother. 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. Theinterposed joint surfaces serve as the support base of the separate segments. From thisviewpoint, 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, therelatively small atlas must provide an upward push equal to the weight of the head plus addedweight 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 isnot in line with both atlantal articulations, cervical muscles opposite to the direction of tilt mustcontract to maintain equilibrium. The muscles and ligaments at the base of the skull serve tocheck the compression and shear forces. When these mechanisms fail, a degree of subluxationmust result. A similar situation occurs in the lower back where a great deal of weight is borne bythe 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 aresome distance from the weight line. This requires constant muscle forces to combat rotational forces tomaintain 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 swayinginvoluntarily anteroposteriorly, laterally, diagonally, and in rotation.

The body is always in motion. Minute oscillatory movements occur in all body parts, whether awake orasleep, 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 soleusand tibialis anterior action. The neuromechanisms are not completely understood, but one theoryholds that body sway is under intermittent autonomic control: a geotropic reflex said by some tobe initiated by position shifts which stretch antigravity muscles and stimulate tonic contractionsto bring the joint towards balance.

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

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

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

The Alexander Technique

F. M. Alexander, an Australian actor, made an important discovery about posture which was published in1924. His findings were confirmed in 1926 by Professor Coighill of the Wistar Institute in London and byDr. Mungo Douglass in 1937 in his text on anatomy. Sir Charles S. Sherrington, the Nobel Prize-winningphysiologist, praised Alexander for his discovery, as did educator John Dewey and Dr. Frank P. Jones,Research Associate at the Tuffs Institute for Psychological Research. Raymond A. Dart, Professor Emeritusof Anatomy and Dean Emeritus of a South African medical school wrote a paper entitled "Anatomist'sTribute to F. Matthias Alexander". The British Medical Journal once published a letter endorsing thetechnique that was signed by 19 prominent physicians. In 1973, Professor Nikolas Tinbergen of Oxford,upon receiving the Nobel Prize for Medicine, devoted half his acceptance speech to the technique.

Claims have been made that utilization of this technique keeps one feeling one's best, streamlines physicalappearance, changes mental attitudes, cures neurotic tendencies, reduces periods of depression, reduceshigh blood pressure, helps symptoms of rheumatism and arthritis, aids the asthmatic, improves circulationand heart function, corrects fallen arches, reduces migraine attacks, improves digestion, correctsinsominia, reduces stress, keeps one young, and many more.

It was Alexander's belief that the mind and body are inextricably bound together to form an inseparablewhole. "A physical act is an affair not of this or that limb solely, but of the total neuromuscular activity ofthe moment." He showed that in everyday physical acts, from the most trivial to the most strenuous, everymotion begins with a slight motion at the base of the skull.

And what were Alexander's findings that have such a wide influence on health? It can be concisely stated:As you begin any movement or act, move your head as a whole upward and away from your whole body,and let your whole body lengthen effortlessly by following that upward direction. If this is done, idealposture will be assumed in any position (Fig. 4.10). Alexander looked to the body segments as a train withthe head as its engine. He felt the key postural reflex or major site of the kinesthetic sense was located atthe atlanto-occipital area, "the crown of the senses". Undoubtedly, Alexander's findings had an influence onB. J. Palmer's emphasis on the upper cervical area.



The Perry Technique

Several variations of the Alexander technique have been developed that have the same or similar objective.For example, Perry, a chiropractor who has gained a wide reputation in treating Olympic and professionalathletes feels that poor running technique can be attributed to poor habits in posture and walking. Onemethod that he uses to improve the technique of such athletes is through "imagery to improve posture." Heinstructs the patient to close their eyes and imagine five helium-filled balloons attached to their body. Aballoon is attached to the vertex of the head, to each pectoral muscle, and to the top of each side of thepelvis. As a reinforcement trigger, he asks the patient to select their favorite color and every time he or shesees that color, or any derivative of that color, to imagine the balloons inflating with gas.

As a result, your pelvis starts to rise, your chest starts to lift, your neck elongates, you feel taller. As yourpelvis lifts, your back will become less tense; as your chest rises, your shoulders and upper back relax; asyour head lifts, the back of your neck relaxes. (88)

Stance and Motion Postures

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 ofgross movement. As discussed previously, the body is always dynamic because of such factors as bodysway, respiration, and restless shifting.

INDIVIDUAL DIFFERENCES IN STANCE POSTURE

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

Weight. Body weight has a distinct influence on the erect posture. The obese have the mosterect posture as a result of supporting the load over the relatively small base of support. Thisposture features twisting while walking with short, stiff steps. A large abdomen requires acompensatory 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 relaxedstance.

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

Military Postures. The military position of attention is an unnatural, immobile position wherethe 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 feetare placed close together with body weight distributed bilaterally. In this position, considerablestress is placed on the erectors of the back and the extensors of the hip and calf. The kneeextensors are more relaxed because the center of gravity falls more anterior to the axis of theknee joint. This posture is difficult to maintain for long periods because of the constant musculartension and the functionally impaired circulation, which can result in pooling within the lowerextremities that leads to cerebral anemia.

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

Effects of Pregnancy. During the advanced stages of pregnancy, the center of gravity isdisplaced considerably forward from the normal because of the increased anterior weight from thefetus, amniotic fluid, and enlarged uterus. Postural compensation is made similar to that seen inthe obese with a large abdomen, but there is a more exaggerated compensatory backward leanwhich 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 thefoot, its shaft is brought to a tangent with the Achilles tendon. Thus, the gastrocnemius andsoleus are able to exert a greater force in plantar flexion. High heels, habitually worn, tend toshorten these muscles and stretch the anterior ankle muscles.

Occupational Effects. Habitual strenuous work results in postural adaptations due to the overdevelopment of asymmetrical musculature or to asymmetries between one part of the body andanother.

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

Standing Surfaces. An elastic floor surface, as opposed to a hard surface, becomes slightlycompressed by body weight to exert a continual force against the foot in an attempt to recover itsoriginal 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 accordwith the immediate goal at hand to be achieved (Fig. 4.11). When one is about to perform a rapid or strongmovement, the posture of readiness is an alert one, reaching its peak between 1 and 2 seconds afterthought is concentrated on the situation. After this peak, posture either becomes relaxed or becomesunstable because of an exaggerated tremor resulting from fatigue of the coordinating centers of the nervoussystem. If no action is anticipated or if the environment is nonexciting, the result is a relaxed posture. Thisposture is so well recognized that the relaxed posture is often used in sports as a ploy to deceive anopponent.

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

Proprioceptive Mechanisms. Postures of alert readiness should not be held motionless for along period because proprioceptive sensations which govern position sense and the relationship ofbody parts will be diminished and must be reestablished before accurate movement can beachieved. 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 adaptingto mechanical forces. Most movements involve lateral shifts of weight which disturb balance andrequire the application of opposing forces to regain balance. Postural shifts of the body's center ofgravity in the vertical direction alter stability but not balance. An ice skater racing forward in thestraightaway leans forward to maintain equilibrium between gravitational force and the drivingaction of the legs. If the torso is held erect, the driving action of the legs should soon topple theskater backward. When skating around a curve at high speed, the skater must lean forward tocompensate for the driving action of his legs and lean toward the inside of the curve to counteractcentrifugal forces.

SITTING POSTURES

In the relaxed sitting position, the head is held erect, balancedover the neck, with the head's center of gravity situated slightlyanterior to the atlanto-occipital joint. Body weight should besupported upon the ischial tuberosities and the adjacent softtissues. The degree of the lumbar curve during the sitting



posture depends upon sacral angulation which is governed bypelvic posture and the degree of mobility/fixation of theinvolved segments.

Editor's Comment: As you can see from Figure4.12, when you sit on the tips of the ischial tuberosity(arrow on the left view), the pelvis (and lumbar spine)rock backwards, flattening and extending the lumbarcurve. Over time, this position stretches out theconnective tissue that stabilizes the posterior elementsof the vertebra and sacroiliac joints, due to plasticdeformation forces. However, IF you "poke your butt"first, before you sit down, you end up sitting on thelower faces of the ischia, rather than the tips (see thearrow on the right), and that will rock your pelvisforwards, reinforcing the lumbar curvature, while alsoreducing the pressure within the lumbar discs. This is agreat strategy for avoiding pelvic misalignment, discderangement, and low back pain in general.

Center of Gravity. In the erect sitting position, the center of gravity is forward of the ischia, thelumbar lordosis is but slightly flattened, and about 25% of body weight is transmitted to the floorthrough the lower extremities. However, in the slouched sitting position, the center of gravity isposterior to the ischia, the lumbar lordosis is reversed, and far less body weight is transferred tothe floor via the lower extremities (Figure 4.12).

Disc Pressure. Lumbar IVD pressure is increased during sitting as compared to the erectposture. The reason for this is that disc pressure increases with the tendency toward lumbarkyphosis. This increased pressure while sitting can be diminished by arm rests on the chair,back support to maintain the lumbar lordosis, and reclining the back of the chair from 90100.

Fatigue. Prolonged sitting (eg, typing, driving) canbe quite fatiguing if strains from imbalance are notavoided. If the head is allowed to protrude forward,the posterior muscles of the neck soon become tiredbecause continuous tension on the erectorsinterferes with their circulation (Figure 4.13). This issometimes a cause of residual neuromuscularhypertension.

Pressure Points in the Sitting Posture. Drummonand associates developed an instrument thatmeasures the pressure distribution during normaland unbalanced sitting. The data collected showedthat the distribution of pressure during sittingindicated that approximately 18% of body weight isdistributed over each ischial tuberosity, 21% overeach thigh, and 5% over the sacrum. (105)

CHAIRS AND DESKS

Chair Design. Chair height should allow the hips, knees, and ankle joints to form anapproximate right angle. The seat should deepen slightly to conform to the increasing thicknessof the thigh as it meets the buttocks. The seat of the chair should be wide enough so that bodyweight can be distributed over a wide area and long enough to support the buttocks and lengthsof the femurs. Bucket-type seats have a tendency to closely confine the body and restrict restlessmovements necessary to improve circulation.

Optimal Support. A reading chair is most comfortable if it is inclined slightly backward and has



arm rests at elbow height. The backrest of the chair should provide support at the hips, lumbarcurve, and shoulders. The upper aspect of the lumbar curve should be supported by a slightconvex curve in the back of the chair. These factors contribute to relaxation of trunk muscles.However, the hollows and curves that make a desk chair comfortable are not desired in anadjustable chair because the hollows and curves no longer fit the body when the chair is tiltedbackward. If a head rest is provided, it should incline slightly forward so that the head and neckare supported in an upright position. If a leg rest is provided, it should be placed at nearly theheight of the seat with a slight tilt forward to enhance venous blood and lymph drainage of thelower extremities.

Seat and Table Height and Inclination. A number of studies have been undertaken in recentyears to determine the ideal seat height and inclination for school children and office workers.Studies by Bendix indicate that the lumbar spine tends to decrease the thoracic kyphosis when atiltable seat is inclined upward 5, especially if this is combined with a slightly increased seatheight. (106) Although inclinations of the pelvis and trunk as well as the posture of the cervicalspine did not change systematically with variable chair-table heights, it was determined in anearlier study that the cervical and lumbar regions of the spine extended and the head and trunkchanged toward a more upright posture when the desk slope was increase during reading. Thisreaction occurred even though EMG analyses of the trapezius showed a low muscular load thatdid not change with varying desk slopes during reading and writing. The conclusion of the studyindicated that a steep slope of the desk was the most favorable for reading while a horizontalsurface was most favorable for writing. (107)

Desks. Both desks and chairs must be adapted to meet individual biomechanical requirements.If a person is seated at a desk that is too low, there is a tendency to lean forward and suspendthe head by force of the posterior neck and upper back muscles. If the desk is too high, there is atendency to spread the elbows and bring the work too close to the eyes.

RECLINING POSTURES

The reclining posture requires little energy expenditure because most gravitational pull is counteracted bythe mattress. Circulatory stress is minimal because energy demands are low and the horizontal positionassists venous return and lymph drainage.

Pillows. Elevation of the head, neck, and upper back helps to relieve respiratory congestion. Asoft pillow aids in preventing chill of the neck and shoulders during cold weather. When in theside position, a pillow helps to maintain vertical alignment of the neck if it is depressed to thesame thickness as the distance from the neck to the tip of the shoulder. However, a pillow of thisthickness used in the supine position would stretch the posterior neck muscles, and this tensionallows little rest for these muscles. Thus, a soft pillow that can be flattened or bunched toaccommodate changes in position is better than a firm pillow. Reading in bed requires a near-sitting position supported by at least two pillows --the back should be supported by a horizontalpillow with the neck supported by a vertical pillow.

DEVELOPMENTAL DEFECTS AND POSTURE

During health evaluation, overall posture should be inspected for early signs of spinal curvature,subluxations, leg-length discrepancies, foot pronation (Fig. 4.14), and other subtle or gross deformities.Both structural and functional deformities result in postural compensations. This is readily apparent in apatient with either a physiologic or structural short leg resulting in a scoliosis that is improved by a shoelift. Pronated feet result in a tilted pelvis and lordosis which are corrected when the pronation is corrected.

Few if any adult spines are free of defects that involve several vertebrae. In many instances, the entirespinal column labors under the strain of improper balance. In this sense, however, the defects of balancereferred to are something less than the classical conditions of clinical kyphosis, lordosis, and scoliosis.

Nature, via genetic factors and its difficulty with phylogenetic increments, commonly leaves the skeleton indefect and instability, and the gross and subtle implications of anteroposterior balance, lateral balance, androtational balance are manifold (Fig. 4.15). The incidence of neck and low back involvements of a protractedand recurring nature is much higher in those patients (especially younger people) whose spines showevidence of developmental defects and anomalies.

Bipedism greatly augments the mechanical and neurologic complications of the lumbosacral complex. Asthe low back and sciatic syndromes are evaluated, no clinician should disregard this fact. Lumbosacraldefects and complications as asymmetrical facet facing, imbrication, sacralization (especially the pseudotype), lumbarization, pars defect, discopathy, iliotransverse ligament sclerosing, retrolisthesis, and L5-S1



reverse rotation are priorities of clinical importance.

Dynamic Postures

The appreciation of the basic biomechanics involved in dynamic posture is the first step in the analysis ofmovement. During gross movements, postural changes affect mechanical equilibrium. Thus it can be saidthat instability is a basic characteristic of body movement. As a result of body instability, rotary forces aredeveloped. These may be beneficial or a hindrance depending, on how they are applied and controlled.Efficient analysis assumes an understanding of biomechanical applications and of neuromuscular controlof the forces of motion in successive postures of movement.

Morehouse/Cooper classify all body movements into:

(1) preliminary movements, (2) a main action, and (3) a follow through. However, the degree of each component varies considerably from action toaction. These factors are clearly demonstrated in athletics because they are often exaggerated foradvantage, but they are utilized in all body movements. Thus, the sports-oriented examples whichfollow should also be identified with nonathletic activities.

PRELIMINARY MOVEMENTS

All main muscle actions are preceded by some degree of preliminary preparatory movement. Generally, thepurposes of preliminary movement are to overcome inertia, control the range of motion, set the direction offorce, achieve mechanical advantage, and initiate speed to gain the momentum desired.

Head Motion and Footwork. Preliminary action serves to overcome inertia, initiate motion, andto place body position advantageously for the main action to come. Frequent shifts in bodyposition, both in and out of sports, are started essentially by head motion (Fig. 4.16). Footworktakes over in importance once the body becomes balanced and is moving in the direction of theforce to be applied. Good footwork reduces uneconomical vertical and horizontal motions that arenot directly related to the task. Thus, footwork can be used to gain optimal momentum bytraveling smoothly with minimal dipping and waddling. Movements that do not contribute to themain action are wasted efforts that decrease movement efficiency.

Range of Motion. The importance of range of motion is readily demonstrated in the golfer's orbatter's preliminary movements. In both instances, the player extends his backswing according tothe force that he wants to hit the ball. When a long hit is desired, the player will shift the hips,rotate the trunk, turn the shoulders, lift his arms, and abduct his wrist to allow the club to arcbehind his head before the forward (main action) power movement takes place. All thesepreliminary actions determine the range of circumferential movement of the club or bat. Likewise,a baseball pitcher or javelin thrower increases his range of motion by extending his active arm,turning his shoulder, twisting the trunk, lifting his contralateral foot, and leaning backward sothat a large forward step can be made during the main forward action. In some actions, time isnot sufficient to allow for wide preliminary movements; for example, in a catcher's throw tosecond base, net play in tennis doubles, or other rapid defensive actions where the backswing ismost short.

Positioning the Center of Gravity. The closer the body's center of gravity is to its base ofsupport, the more stable it is. For this reason, a tightrope walker holds the pole low and the poleis weighted at both ends. During a somersault, an acrobat lands in a deeply crouching positionwith the hands held low to keep his center of gravity low. Likewise, a shot putter helps tomaintain his balance after a throw by lowering himself to a squat. Flexed knees, a forwardcrouch, and hands held low help the surfboard rider maintain balance by maintaining a lowcenter of gravity. During a slow run, there is little body lean; but when speed is to be increased, agreater forward lean must be started before powerful leg action is initiated if balance is to bemaintained. Conversely, a backward lean must be initiated before a fast run is reduced orstopped. The greater the lean during a fast run, the more difficulty there is in changing directionwithout a loss in balance. If direction is to be changed, the center of gravity must be shiftedtoward the new direction and shorter strides must be taken. In most all cases, these changes indirection are initiated by a head movement; eg, forward in increasing speed and backward indecreasing speed.

Leverage. Preliminary movements can employ body parts for optimal mechanical advantage.Several examples of this are demonstrated in sports techniques. It is much easier to push or pullwhen the body is slightly leaning anterior than when it is erect. This forward lean contributes



weight and leverage to the arms and lowers the body's center of gravity. A gymnist grips ringswith the proximal aspect of the palms rather than the fingers to shorten the resistance lever armabout 3 inches. During a swimming start or a basketball center jump, the athlete crouches,flexing his hips, knees, and ankles at a right angle so that the joint extensors are placed at theirbest mechanical advantage. In throwing, the elbow placed at a preliminary right angle offersoptimal mechanical advantage to the triceps and anconeus muscles for elbow extension. Inbaseball, the batter's forward elbow is carried high so that the triceps can pull forcibly on the bat.

Stabilization. If the trunk is held loosely during arm and leg actions, some extremity forces willbe diverted to stabilize the torso. It is for this reason that efforts in jumping, lifting, pushing,pulling, and throwing are enhanced if the breath is held and the abdominal muscles fixed duringthe main action.

Utilizing Large Muscles. Preliminary movements bring the most advantageous muscle groupsquickly into action. When the larger muscles are used for a main action, the result is a powerfulaction. A chin up, for instance, is easier performed when the palms are supinated to allow thepowerful biceps to be the major force. If the hands are pronated, the weaker brachialis andbrachioradialis must overcome the load. During hand wrestling, a far greater force can be exertedif the large muscles of the shoulder, back, thigh, and legs are utilized than if only the muscles ofthe arm and forearm are used.

Coordination. Coordination may be defined as the ability to integrate separate abilities in acomplex task. Limb motion or the addition of a load shifts an individual's center of gravity andchanges body balance, and how one copes with gravitational influences may be witnessed in aperson's degree of coordination. Well-coordinated movement, usually involving the large musclesin sports, requires perfect timing between the nervous and muscular systems, for example asseen in the biologic teamwork expressed in bowling, gymnastics, badminton, throwing, jumpinghurdles, handball, tennis, ice hockey, hitting a baseball or golf ball, or kicking a soccer ball. Infast movement of light loads, the antagonists must relax before the prime movers contract. Inslow movement of heavy loads, the antagonists stabilize the levers involved in the movement.During fatigue, muscles become tensed and are unable to exhibit efficient teamwork; thusoptimal skill, force, speed, steadiness, accuracy, and endurance are lost.

Momentum. A left-handed batter in baseball can effectively utilize the momentum of the bat toovercome inertia and start his run to first. Likewise, if a fielder can catch a fly ball on the forwardrun, this momentum will add to the force of his throw. In the basketball jump, the player shouldextend his tipping arm before the main action or the movement during the main action willproduce an equal downward force toward the torso and reduce the force of pushoff. Duringthrowing, the arm is first driven sharply backward to initiate the forward movement (Fig. 4.17).The swimming start requires that both arms be thrown backward.

MAIN ACTIONS

Body Bulk. Body bulk has both advantages and disadvantages. Muscle bulk, especially incontact sports, provides both force inertia and protection for bones and joints. Body weight is lessa consideration in rowing and swimming sports because the weight is supported, it offers somebuoyancy advantages, or it provides necessary insulation from subcutaneous fat (eg, open-waterswimming). Due to gravitational pull, a heavy bulk is a disadvantage in running sports as it mustbe raised at each pace. There are also disadvantages in that bulky hypertrophy increases viscousresistance to movement, produces problems from physical apposition, and increases the bodymass to be moved. Thus, to avoid mass accumulation in an irrelevant part of the body, muscletraining should be specific for the use desired. Indiscriminate muscle hypertrophy is likely toimpair performance in endurance events.

The Critical Moment. In any movement there is a critical moment. This is seen at the instantwhen a hockey stick contacts a puck, when a bat contacts a baseball, when the throwing hand isabout to release a bowling ball, or when the foot of a soccer player is in contact with a ball. Ineach case, the critical moment is very brief and the forces are usually great. There is little timefor correction at the moment of contact or release. At this critical moment, the forces are resolvedso that they act in a straight line, thus the force must be in line with that desired for a fraction oferror during impact or release will be magnified by the distance the object travels.

Agility. Agility involves speed with the addition of a sudden change in direction or height suchas in a defensive maneuver or a change in attack the ability to change positions in space. Thenumber of positional changes available is obviously almost endless, and thus agility is mostdifficult to evaluate. Good agility is demanded in the sports of hockey, gymnastics, diving, boxing,and karate, and in the positions of running back and infielder.



Base of Support. The larger the base of support (eg, large feet or wide stance), the greaterimpact can be received without toppling. Thus, a boxer who stands with his feet spread in thedirection of a blow is more difficult to knock down. This is because the center of gravity canprescribe a wide arc about the central base before it falls perpendicular outside the base ofsupport. When the legs are outspread, the angle of maximum lean is enlarged.

Balance. Balance is a necessary attribute whenever one's base of support is reduced yet bodyposition must be maintained. Standing, walking, running, bending, throwing, and contact sportsall require constant voluntary loss and regain of body balance. The human body tries to maintainits upright posture with the head positioned so that the field of vision is parallel to the horizonand straight ahead. During linear motion, balance is maintained only if forces acting in otherdirections are in equilibrium. If balance in the direction of action is not maintained duringmotion, the accuracy of striking or throwing will be reduced. Once balance is lost, force economyand direction are interferred with, neuromuscular coordination and speed are inhibited bytension, and agility is reduced. Rarely can an imbalanced preliminary movement be correctedduring the main action unless the person is highly trained in achieving instantaneous alterationsin timing or form. Even then, the muscular attempts to re-establish equilibrium dilute the muscleforce necessary for the main action. Precise ballet-like balance is required in such sports astight-rope walking, hand standing, surfing, karate, hockey, skiing, and to a varying degree inmost ball-playing sports where movement is required in an "off-balance" position.

Delivering Impact. Whether impact is delivered or received, its force will be in accord with therelative velocities and mass of the colliding bodies. Thus, greater impact force can be made with ahip than an elbow as the trunk has greater mass. When impact is made by elbow or kneeextension such as in throwing or kicking, a great velocity must be developed. The summation offorces can be used (eg, in boxing) to increase impact force by adding a second blow at the instantof the peak of the force from the first blow which will be much greater than blows deliveredsimultaneously or separately.

Receiving Impact. Postural adjustments just prior to receiving an impact (eg, like utilizingone's center of gravity, going with the direction of force, and prolonging the duration of impact)can diminish its force. For example, a toppling force can be minimized by receiving the impact asclose to one's center of gravity as possible. An impact force can be reduced by moving in the samedirection as the force; ie, rolling with the punch. The peak force of impact can be lessened byprolonging the duration of impact such as allowing the hand to be carried backward whencatching a ball or changing direction toward the line of a body block. Rolling on impact or hittingan elastic surface can reduce the peak force of a fall (Fig. 4.18).

FOLLOW THROUGH

Follow through has no effect on an object after impact, but it has an important function in preventinginjury. It is for this reason that the baseball pitcher's arm must be allowed to continued its horizontal arcand the softball pitcher's arm to follow its vertical arc to dissipate the forces initiated within the arm. In allpowerful movements, the main action should be allowed to continue and gradually decelerate within therange of motion to save injury or fatigue to check ligaments and muscles.

The Walking Function

Biomechanically, walking can be considered as a series of continuous losses and recoveries of balance inwhich the rhythmic play of muscles narrowly averts toppling. Steindler refers to the basic sequence ofmovements in walking as a "series of catastrophies narrowly averted." This is a constantly changing processthat includes starting, speed and directional changes, adaptive changes to slope or surface conditions,modifications to neuromusculoskeletal disorders and energy requirements, physical proportions,adaptations to heel height and footwear, and stopping movements. However, all these motions aretransitory movements that are superimposed on individual basic patterns of rhythmic displacement whoseobjective is progression towards a goal.

On level ground, walking can be considered biomechanically as forward translation of the body's center ofmass. This requires an external force, provided essentially by the extensors of the hip and knee and theankle plantar flexors, whose efficiency is governed by the friction produced between the foot and the floorduring push-off.

BACKGROUND



It is typical during the chiropractic examination to study the patient in the static standing position andduring gross movements with the feet relatively fixed in the standing or Adams positions and the pelvisrelatively fixed in the sitting position. While these procedures offer vital information, they fail to detectmany subtle adaptive mechanisms brought out by carefully viewing the patient during progression. Thislatter technique requires training and experience as the alternating movements occur rapidly even duringslow walking. Attention must be directed to many aspects simultaneously. Photographic stills are helpfulbut impractical in the typical clinical situation.

A walking cycle equals one stride: two steps, one with each lower limb. During a walking cycle, stride lengthdetermines the body's segmental displacements and the frequency or duration of the stride governs the timeinvolved. Stride length is essentially determined by an individual's leg length. These two factors, time anddistance, are the major factors contributing to a person's particular gait.

Newton's second law should be kept in mind when analyzing gait. The floor pushes up against the plantarsurface in locomotion with an equal force and along the same line of action as that of the force of the foot.However, this counterforce of the floor or ground may fail (eg, loose rug, gravel, sand, soft mud). In addition,an equal and opposite horizontal force, usually supplied by friction, must accompany pushoff if progressionis to take place. This is greatly reduced or fails to happen on a slippery surface. When walking on a slipperysurface, a long stride is more apt to lead to a fall because of the angle at which the heel hits the surface. Ashort stride allows the foot to descend in a more vertical direction.

Walking is the result of muscle action developing tension and producing joint rotations (angular changes).Body weight is balanced over the hip joint by the abductor muscles acting through the greater trochanter --a first class lever system. In walking, body weight acts medial to the knee in such a manner that the centerof rotation or fulcrum is centered over the medial condyle. Equilibrium is controlled by forces acting in thelateral ligaments, biceps femoris, and tensor fascia lata.

INDIVIDUAL DIFFERENCES IN WALKING PATTERNS

Ectomorphic, mesomorphic, and endomorphic body types have different types of gait, and there is greatvariation within these general categories. It is not unusual to recognize a person at a distance strictly byhis or her gait. Each of us has a characteristic walking pattern that is altered by both mood andenvironment. In addition, injury frequently alters normal axes of movement, restricting some andexaggerating others. Thus, any description of gait is a generalization that points out gross similarities ofsegmental motion.

THE GAIT CYCLE

The normal gait presents smoothness of function without any sign of impairment or afflection of parts ofthe body. The normal walking cycle is considered to have two phases:

(1) a stance phase, when the foot is in contact with theground; and (2) a swing phase, when the foot is moving forward in the air (Fig. 4.19).

During normal walking, one leg is in the stance phase while the other isin the swing phase. Muscles mustcontract to counterbalance the forces of gravity, to offer acceleration or deceleration to momentum forces,and to overcomethe resistance of the walking surface.



The Stance Phase. About 60% of the walking cycle is used in the stance phase. Because thestance phase is the weight-bearing phase requiring the greatest stress, most problems willbecome 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 measuredfrom 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. Midswingrepresents the transition period between acceleration and deceleration.

BODY OSCILLATION

A wheel is efficient in forward translation becauseits center of mass is kept parallel to the ground. Inthe human, however, there is considerable up anddown, side-to-side, and rotational oscillation aswell as linear translation (Figure 4.20). Thus,force is required for vertical, lateral, and rotationaldisplacement that must be added to the forcenecessary for forward movement. Any disorderthat increases oscillation is energy consuming andlinear speed reducing.

High Points. As previously explained, thecenter of mass of the body is that point wherethe mass movements on one side of any planeare equal to the mass movements on theother side. During gait, the high point ofvertical oscillation (about 2 inches) andlateral displacement are reached whenunilateral weight is greatest and the lowerextremity is in full extension. This occursnear mid-stance of the single-supportinglimb and midswing of the non-weight-bearinglimb. Also, the highest point in elevation ofthe center of mass occurs when body velocity is lowest, and vice versa. This upward movementbegins just after the center of mass has passed anterior to the weight-bearing foot as the body'smomentum carries the body up and over the leg in stance. Immediate fall of the center of massafter it has passed over and in front of the weight-bearing foot is delayed by the relativelengthening of the weight-bearing leg via knee extension, ankle plantar flexion, and footsupination. 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, thegreater the vertical excursion. This low point where both feet are in contact with the ground, onefoot at toeoff and the other at heelstrike, normally accounts for 15% of the gait cycle. This is theperiod of double support, and its duration shortens as walking speed increases. In running, theperiod of double support is zero.

Stress Points. The depth of the low point depends on the degree of pelvic rotation and lateralshifting during the period of double support, while the height of the high point depends on thedegree of pelvic tilt and knee flexion during footflat. The high point places stress on both theweight-bearing hip and knee; the low point places stress only on the hip as the knee is relativelylocked in extension. Flattening the arc of the body's center of mass during translation ismaintained 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 (46) awayfrom the leg in stance and toward the leg in swing from the force of gravity (positiveTrendelenburg). This alternating angular displacement at the hip joint is maximum at midswingon the side of the swinging leg. Pelvic tilt is essentially controlled by contraction of the hipadductors 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 swingmust flex so that the foot will clear the floor. Tilting appears exaggerated in the female because ofthe wider pelvis and greater superficial fat.

Pelvic Rotation. Relative to the line of progression, the pelvis alternately rotates toward theright and left about a vertical axis during typical gait. This somewhat stabilizes the center ofmass by reducing abrupt changes in oscillation arcs which tends to reduce the severity of impactat surface contact. During hip extension and flexion, angular displacement is reduced and theforce necessary to change direction of the body's center of mass in the following arc of translationis reduced. Pelvic rotation occurs anteriorly on the side of the advancing limb during the swingphase and posteriorly during midstance. These alternating rotations occur essentially at the hipjoints due to the relative rigidity of the pelvis. The movement is maximum just before heelstrike,moving 35 on either side of the central axis. As speed is increased, this value increasesbecause there is a corresponding increase in stride length.

Pelvic rotation in the transverse plane on a fairlylevel surface has long been known to be aninstinctive energy-saving mechanism because itincreases stride length with minimal effort duringgait. This mechanism of pelvic rotation has beenconsidered by some to be lost during themetabolically expensive exercise of walking orrunning uphill or downhill. Wall and associates,however, have shown that this belief is not true.(142) Data recorded from subjects walking on atreadmill that had been sloped plus or minus 20%showed that pelvic rotation on a 20% incline wassubstantially the same as that on a level surface.

Lateral Sway. Besides pelvic tilt and rotation, adegree of alternating horizontal displacementoccurs to replace the gravity line nearer the hip ofstance (Figure 4.21) during the period of singlesupport. Its rhythm is one-half the frequency ofvertical displacement. It reaches its greatestdegree following midstance on the weight-bearingleg and constitutes about a 2-inch lateralmovement of the center of mass with eachcomplete stride. This is seen as an adduction movement of the stance side, as is pelvic tilt. Onceits peak of lateral displacement is reached, the pelvis begins to reverse direction. This horizontalsway increases the base of support about 4-8 inches as the feet pass each other. There isnormally a slight degree of genu valgum that allows the leg to remain essentially vertical and thefeet close together during gait hip movements. When the lateral distance between the feet isincreased 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 minimizedby slight flexion of the hip and knee during midstance. This flexion moves the gravity line anteriorto the hip and posterior to the knee. The greater the degree of this flexion, the greater effort isnecessary 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 isfollowed by extension, and then flexion occurs again during pushoff and swing. The knee joint isalmost fully extended at heelstrike and then begins to flex to about a maximum of 15 untilfootflat. Just prior to full weight bearing, the knee again passes into extension. Note that thecenter of mass is in a state of dropping at the point of heelstrike. This drop is decelerated byslight knee flexion against quadriceps resistance.

Ankle and Foot Flexion and Extension. At the ankle, dorsiflexion, plantarflexion, and rotationoccur 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 arcaround the radius formed by the heel at heelstrike and about a center point in the forefoot atpushoff. That is, the foot is plantar flexed against tibialis anterior resistance after heelstrikearound a point where heelstrike occurs. Rotation about this point tends to shorten the legrelatively 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 andtibialis anterior contraction acting on the foot. Added to these mechanisms is the fact that theankle pronates slightly during full weight-bearing midstance. During a typical walking cycle, heelelevation changes are about twice that of the ankle and toes, while ankle and toe changes are 2-3times those of the knee and hip.

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

Arm Swing and Spinal Rotation. Althoughswinging the arms has no effect upon shifting thecenter of mass during body oscillation, it providesa means of neutralizing total angular momentum(Figure 4.22). That is, the leg advance and pelvicrotation that produce an angular momentum tothe lower body are balanced by a reverse angularmomentum of the upper body aided by arm swingresulting from shoulder rotation. During normalgait, these rotations are about 180 out of phasewith rotation of the pelvis. That is, maximalforward arm swing occurs contralateral to swing,and backward arm swing occurs contralateral tostance. This helps to control weight over thestance hip, maintain forward momentum, andsmooth forward progression of the body as awhole. The inertia of the arms is overcomeessentially by the alternating lumbar rotationtowards the side of the low pelvis which iscompensated by a reverse rotation of the thoracicspine.

Vertebral Motion. Because of out-of-phaseshoulder and pelvic rotations during gait, theremust be points of minimum and maximumtransverse rotation. Keep in mind that the pelvis rotates anteriorly and the shoulder rotatesposteriorly on the side of the swinging leg, and vice versa. Studies have shown that the upperthoracic vertebrae rotate to a degree about equal to that of the shoulder girdle and the lowerlumbar 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 weightsare 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 plantarflexion and outward on dorsiflexion. When the foot is fixed on the surface during stance, relativeplantar flexion produces external rotation of the leg and dorsiflexion causes internal rotation. Theprimary mechanism here is the subtalar joint, a single-axis hinge joint whose axis is inclinedabout 45, which allows transverse rotation of the tibia. Without this, the foot would have to slipupon the walking surface. It is interesting to note that the foot must change from a flexiblestructure 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. Pronationoccurs as the foot is increasingly loaded. When body weight is transferred from the heel to theforefoot 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 archmedially and depresses it laterally, tending to shift body weight laterally during maximum weightbearing. At pushoff, the foot deviates laterally to distribute weight between all the metatarsalheads. Evidence of this is shown by the oblique crease in the shoe where the vamp and the capjoin. This crease is over the metatarsophalangeal joints and will vary with individual differencesin 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 walkingindividual 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 atfootstrike. It is also for these factors that obese people tend to walk with a waddle. A mother oftencarries a young child between her hip and ribs (or on the lower back or top of the head in somecultures) 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 changesoccurred in the electrical activity of gait muscles following manipulation of the lower extremity articulationsto reduce malposition, while the electrical activity of control subjects decreased only slightly. (145) Hibbardalso cites the work of Rebechini-Zasadny and associates that had earlier found a significant difference inthe 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 thedoctor of chiropractic determine postural changes resulting from an unnatural gait. For instance, ashortened leg gives a characteristic limp. A stiff knee causes the affected limb to swing outward whilewalking. Intermittent claudication or limping is observed in chronic peripheral vascular diseases such asendarteritis 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 holisticbiomechanical 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 motionmay require a frustrating conscious effort such as that taken by a healthy person stepping into a canoewhere the support is unfamiliar.

Although children emulate adult gait in many respects, there are differences that must be considered inanalyzing 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 asthose of adults.5(155)4 However, accelerations, velocities, and linear displacements were consistently largerfor 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 nothad an opportunity to witness this previously. The chair should be one that gives firm sitting support andprovides 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 thechair to the standing position. Note the needed base of support: how far the knees are apart and how farthe forward foot is from the back foot. If the chair has arms, note the degree the hands are used fromsitting to standing to assist weak knees, weak hip extensors, or to maintain stability, balance, andcoordination.

NORMAL STANCE AND SWING PHASES

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



During normal ambulation, the normal range of motion at the ankle is from 20 plantar flexion to 15dorsiflexion. The knee moves 65 from flexion to extension. At the hip, about 6 of adduction occurs and a45 range is necessary from flexion to extension.

After the walking sequence has been initiated, the movements are normally continued in a rhythmicmanner solely by reflex actions. The stretch reflex of the antagonistic extensor muscles is reflexly inhibitedas the flexors of the hip, knee, and ankle are stretched. Walking actions are maintained by the reflexiveinterplay 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 totoeoff, 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 actionsshould be analyzed.

HEELSTRIKE

Inspection. At heelstrike, the ankle is between dorsiflexion and plantar flexion, the knee is fully

Clinical biomechanics_ Body Alignment, Posture, And Gait

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