Posterior Pelvic Till

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Two types of posture exhibit posterior pelvic tilt, hip joint extension and weakness of the iliopsoas muscle.

The flat-back posture, as the name implies, is a straight back in both the lumbar and thoracic areas, except that some degree of flexion in the upper thoracic area accompanies the forward head position.

The sway-back posture is one in which there is posterior displacement (i.e., swaying back) of the upper trunk and anterior displacement (i.e., swaying forward) of the pelvis. A long kyphosis extends into the upper lumbar region, and the lower lumbar region is flattened. The posterolateral fibers of the external oblique are elongated. (See accompanying illustrations and pp. 70, 71.)


In the past, the words lordosis and sway-back were used interchangeably in referring to the curvature in the low back and lower thoracic areas. The postural differences between the lordosis and the sway-back postures were recognized in Posture and Pain, but the name sway-back was not applied until the third edition of Muscles, Testing, and Function, published in 1983. Separating the use of these terms also differentiated the two postures, which are, in fact, distinctly different with respect to the an-teroposterior tilting of the pelvis, position of the hip joint, and accompanying muscle imbalances. Weakness of the iliopsoas is a constant finding in the sway-back posture, in contrast to being strong in the lordotic posture. As determined by the lower abdominal muscle test, the external oblique is usually weak in both the lordotic and sway-back postures.

The postures resemble each other in that both involve a curve in the back. In the lordotic posture, the anterior curve in the low back is increased. In the sway-back posture, however, there is an increased posterior curve in the thoracic and thoracolumbar regions. In the lordotic posture, strain is usually felt across the low back; in the sway-back posture, strain is more often felt in the area of the thoracolumbar junction.

Treatment aims to restore good alignment, with the low back in a normal anterior curve and the upper back in correction of the long kyphosis. A properly fitted support should be considered if the posture has become tt » )jy

Flat-back posture. Sway-back posture.

painful or if the upper back and lower abdominal muscles are too weak to maintain postural correction. Exercises to strengthen the iliopsoas and the lower abdominal muscles are usually indicated for subjects with the sway-back posture. Alternate (but not double) leg raising from the supine position with the low back held flat on the table may be used for hip flexor strengthening.

From a neutral position of the pelvis, the range of motion in the direction of the posterior tilt is less than in the direction of anterior tilt. The same four muscle groups support the pelvis anteriorly and posteriorly: anterior abdominal muscles, hip flexors (chiefly Iliopsoas), low back muscles and hip extensors.


When describing the flat-back posture, it is necessary to recognize two types: one that is flexible, which is the more common type, and the rigid, flat low back. Because normal flexion is defined as flattening or straightening of the lumbar spine, both types of flat-back posture exhibit normal flexion. In the flexible back, extension is not limited; but in the rigid back, extension is limited. (The latter is not included in the following discussion.)

The flexible flat-back posture appears to be more common among certain cultures. Asians, for example, seem to exhibit this type of posture more frequently than Americans or Europeans. This type of flat-back does not give rise to as many problems of low back pain as do the lordotic back and the sway-back postures. The range of motion in extension is usually normal and may even be excessive.

The low back muscles are strong. The abdominal muscles, especially the lower, tend to be stronger than average. The hip extensors are usually stronger, and the hamstrings often show shortness. Consistently, the one-joint hip flexors (mainly the iliopsoas) are weak. This weakness is not evident in the usual group hip flexor test in sitting, but it is evident in the supine test for the il-iopsoas (See p. 423) and in the test requiring completion of hip joint flexion in sitting (See p. 424). If the hamstrings are tight, stretching exercises are indicated (See p. 390).

The following observation was made by the original senior author of this text in a 1936 publication:

In my experience I have not come in contact with a patient having a normally flexible so-called flat-back, with a balance between the strength of the back and abdominal muscles, who has complained of chronic low back pain. . . . The weight-bearing line of the body is nearly normal in these patients and they do not exhibit the type of chronic low back pain associated with extreme faulty posture (9).

Careful consideration must be given to examination findings when planning a course of treatment. It is a mistake to assume that extension exercises are indi-cated—they may be unnecessary or even contraindi-cated. The flat-back posture is one in which the hip joint is in extension and the hamstrings are strong and usually short.

If this type of posture exists without low back pain, it is not necessary to change it. If the back is painful, however, and restoring the normal anterior curve is indicated, the measure of choice should be strengthening the weak hip flexors. The problems with back extension from the prone position are, first, that it involves strong hip joint extension and extensor muscle action to stabilize the pelvis to the thigh for the trunk to be raised and. second, that the hip extension stretches the already weak iliopsoas.

If low back extension is indicated, for whatever reason, it can be done in a sitting position, or by the stabilizing action of the low back during alternate leg raising in a prone position—raising the leg only about 10° in extension.


Excessive flexion (i.e., hyperflexion) of the lumbar spine is not uncommon. It is seen as a kyphosis of the low back in sitting, but it rarely appears as a kyphosis in standing. (See photograph, p. 377.) In most cases of excessive low back flexion, the back extensor muscles are not weak, but the hamstrings are often tight. (See pp. 175 and 389.)

Some individuals with excessive flexion in sitting will stand in a lordotic position. Certain exercises promote excessive flexion of the low back as they strengthen and tend to shorten the hip flexors. Notably, the curled-trunk sit-up from a knee-bent position creates a demand for complete curling of the trunk, including the lumbar spine, and exercises the iliopsoas in hip joint flexion almost to completion of the range of motion.

With a painful low back and hypermobility in flexion, the treatment of choice is a support that prevents excessive range of motion. If the hamstrings are tight and exercises are done to stretch them, one should avoid forward bending, and one should wear the back support while doing passive or active straight-leg raising. (See p. 390.)


Problems of postural low back pain associated with lateral pelvic tilt are common, but many such cases go undetected. The mechanical problem is chiefly one of undue compression at the articulating facets of the spine on the high side of the pelvis. The sore spot that corresponds with the area of greatest compression is usually over the articulating facet of the fifth lumbar vertebra on the high side.

In cases of lateral pelvic tilt, muscle imbalances are usually present in the lateral or posterolateral trunk and in the lateral or anterolateral thigh muscles. The pos-terolateral trunk muscles and lumbodorsal fascia are tighter on the high side of the pelvis, whereas the leg abductors and tensor fasciae latae are tighter on the low side of the pelvis. On the high side, the leg assumes a position of postural adduction in relation to the pelvis, and the abductors (particularly the posterior part of the gluteus medius) show weakness. (See figure, p. 435.) An imbalance may also be noted in the hip adductors.

The pattern most frequently seen in right-handed individuals is that of a tight left tensor, a weak right gluteus medius, and stronger right hip adductors and right lateral trunk muscles. Left-handed individuals tend to show the reverse of this pattern; however, their acquired patterns of muscle imbalances tend to be less fixed than those in right-handed individuals. Equipment and tools are most often designed for right-handed use if an element of asymmetry is involved, and left-handed people are required to use these instruments in a right-handed manner.

As a result of faulty lateral alignment and muscle imbalances, pain may appear in the low back or in the leg. Careful examination often reveals problems in both areas, regardless of the area in which the chief complaint is located.

Treatment is primarily concerned with realignment and, essentially, consists of applying a straight raise on the heel of the shoe on the low side of the pelvis. Seldom is it necessary or advisable to use a lift more than 78- or Vi6-inch thick. A firm rubber and leather heel pad that can be inserted into a shoe often suffices.

The difference in level of the posterior spines, as seen when the patient is standing with the knees straight, should provide the basis for determining the need for and the amount of shoe lift. Unfortunately, apparent leg length measurements taken in the supine position as a basis for determining the side of application of the lift are often misleading. (See analysis of fallacy in this regard, p. 438.)

If the tensor fasciae latae is tight on one side, the faulty alignment will not be corrected automatically by the application of a shoe lift. It may be necessary to treat this tightness even though no specific symptoms are present in the area. Such treatment should precede or accompany the use of a shoe lift and may consist merely of active stretching exercises or of assisted stretching. (See pp. 398 and 450.)


Discomfort, aching, or in some instances, pain may be present in the area of the posterior gluteus medius muscle. Symptoms may start as an annoying discomfort in standing and may progress to ache in standing or side-lying. In side-lying, it may hurt whether lying on the affected or on the unaffected side. Habitually standing with the weight on one leg more than the other gives rise to stretch weakness that, if it persists, can result in the complaint of discomfort or pain. Treatment may be as simple as breaking the habit of standing with the weight shifted toward the affected side.

The weakness of the gluteus medius, which is usually present on the high side of the pelvis, must be corrected to maintain good lateral alignment. A shoe raise on the opposite side, which is used to level the pelvis, removes at once the element of tension on the weaker medius provided that the subject stands evenly on both feet and avoids standing in adduction on the side of the weak medius. As a general rule, specific exercises for the gluteus medius are not necessary for individuals who are normally active; the exercise involved in the ordinary, functional activity of walking usually suffices for strengthening this muscle.

A minimum of 6 weeks is generally advisable for the wearing of a lift. Whether the lift is needed for a longer period depends to a great extent on how long the immediate postural problem has existed, whether any actual leg-length difference exists, and whether occupational activities or postural habits can be changed to permit the maintenance of good alignment.

Even though it may be slight, some degree of rotation of the pelvis on the femurs usually accompanies a lateral pelvic tilt. The pelvis tends to rotate forward on the side of a high hip. In other words, counter-clockwise rotation of the pelvis usually occurs when the right hip is high and the right leg is in postural adduction on the pelvis. This rotation tends to disappear when the pelvis is leveled laterally.

Because low back pain is often caused or triggered by the act of lifting, a brief discussion of this topic is in order.

Much has been written about how to lift, conditions in the workplace that need to be corrected, and problems as they affect the lifter. The weight of the object to be lifted, the frequency and duration of lifting, and the level from which an object must be lifted are all matters of concern with respect to how the lifter is affected.

Because of the many variables involved in lifting, there cannot be a single correct way to lift. Some points of agreement, however, relate to the lifter and to the object being lifted:

Stand as close to the object as possible.

Stand with the feet apart and one foot slightly in front of the other.

Bend the knees.

Begin the lift slowly, without jerking.

Avoid twisting in the forward-bent position.

There is also agreement that lifting from floor height presents many hazards. It is preferable that objects not be at floor level. If this is not an option, an assistive device should be used, if possible.

Opinions differ regarding whether to squat or to stoop and whether the low back should be straight or curved anteriorly (i.e., in the direction of a lordosis). Squatting involves moderate knee bending; stooping involves bending forward from the hips or the waist (or both) and slight knee bending.

The squat lift has been advocated as a means of placing the load more on the legs and reducing the load on the back. The squat position for lifting, however, places the quadriceps at a mechanical disadvantage and makes it subject to severe strain. Furthermore, many people have knee problems that prohibit lifting from a squat position. Some may tolerate this position but lack the necessary quadriceps strength for a job that requires this type of lifting. Deep knee bending has been discouraged in exercise programs for a long time, and the squat position should not approach that of deep knee bending for lifting.

In many instances, the squat lift is not an option, and there is no alternative but to stoop. Lifting an infant up from a playpen, helping a patient get up from a chair, and lifting objects from the level of the thighs to a higher position are examples of situations in which stooping is required.

The mechanics of lifting is important, but the body mechanics of the lifter is even more important. The decision regarding how to lift must take into consideration the ability or vulnerability of the lifter. Of major concern are the mobility, stability and strength of the lifter. In the general population, the mobility of the low back varies widely, ranging from excessive to limited. Excessive flexion and excessive extension both represent potential problems related to lifting. Limitation of motion to the extent of stiffness in the low back presents the problem of undue strain elsewhere (if not in the low back itself).

In forward bending, some people exhibit excessive flexion (i.e., hyperflexion) in which the lumbar spine curves convexly in a posterior direction and assumes a position of lumbar kyphosis. This condition is not uncommon. Although the low back muscles remain strong, the posterior ligaments are stretched and the back is vulnerable to strain when lifting. When this condition exists, the treatment of choice is the use of a support that prevents excessive flexion when lifting. The alternative is to attempt to hold the back in a neutral position by strong co-contraction of the back and abdominal muscles.

Some people exhibit excessive extension in which the lumbar spine curves convexly in an anterior direction and assumes a position of marked lordosis. Referring to the work of Fami, Pope et al. stated that "as the lumbar lordosis increases, the plane of the LS and SI disks becomes more vertical and subject to greater shear and cyclic torsional forces, while nonlordotic segments are subject to compressive forces" (26,27). Referring to the work of Farfan. Pope et al. also stated that "[Blending and torsional loads are of particular interest, since the bulk of experimental findings suggest that these, and not the compressive loads, are the most damaging to the discs" (27,28).

The normal anterior curve in the low back is a slight curve that is convex anteriorly. It is not a stable position—movement can take place in either an anterior or a posterior direction. Furthermore, no stability is afforded by ligamentous restraint in either direction. Trunk muscles must be called on to stabilize the trunk.

When it is advocated that the back be held in a normal anterior curve (or in some degree of lordosis) during lifting, the question arises about precisely what muscles must come into play to hold that exact position. If the back muscles contract unopposed, the anterior curve and anterior pelvic tilt increase, and the potential for overwork of the muscles and injury to the low back also increase and predispose the subject to an added problem. Referring to work by Poulson et al. and Tishauer et al., Chaffin stated that "lumbar muscles (like all skeletal muscles) suffer ischemic pain when statically contracted for prolonged periods of moderate to heavy loading" (29-31).

The opposing force that prevents an increase in the curve must be provided by the anterior abdominal muscles (most specifically the lower abdominals). Tests and exercises specific to these muscles should be applied. Weakness of the lower abdominal muscles is a common finding among otherwise strong individuals, and it presents a potential hazard in regard to lifting. Strengthening the abdominal muscles, however, can affect more than merely the stability of the back. Pope et al. found that "intradiscal pressure fell when abdominal pressure was increased. Thus in the standing posture intradiscal pressure is decreased coincident with increased abdominal muscular activity" (27).

The accompanying photographs are of a weight lifter who developed a backache and had to stop lifting until he built up strength in his abdominal muscles. He then returned to weight-lifting and demonstrated the manner in which he would pick up a heavy object from the floor. For those with weakness of the abdominal muscles who continue weight lifting, it is advisable to use a support that provides abdominal and back stabilization.

Many individuals will exhibit a flat low back in the forward-bent position. Flexion of the lumbar spine is movement in the direction of straightening the low back, and a flat low back represents normal flexion. When the low back flexes to—but not beyond—the point of flattening, stability is afforded by this limitation of motion, just as there is stability at the knee joint if it does not hyperextend. In the back, this limitation provides a "built-in chair-back" that gives stability when lifting with the back straight.

The potential for strain of the low back muscles and ligaments exists with hyperflexion, and the potential for ischemic pain with the lordotic back; disk problems may result from either (32).

From the standpoint of prevention, one must assess how some exercises adversely affect the body in relation to the potential hazards in lifting. The knee-bent sit-up is conducive to excessive low back flexion as well as to overdevelopment and shortening of the hip flexors. For many adolescents, the legs are long in relation to the trunk and there is a tendency for tightness in the hamstrings. Forward bending to reach to or beyond the toes often results in excessive back flexion. Press-ups in the prone position that emphasize back extension to the point of fully extending the elbows encourages excessive range of motion in extension.

With an emphasis on maintaining or restoring good body mechanics and muscle balance, or on compensating for deficits by means such as necessary bracing, fewer problems of low back pain will occur from lifting.


Weakness of the low back is seldom seen in ordinary faulty posture problems. The low back muscles are an exception to the general rule that muscles that are elongated beyond normal range tend to show weakness. For a striking example, see p. 377 for photographs of a subject who has excessive flexion, but normal back strength (seep. 171).

Marked weakness of Erector spinae muscles is not seen except in connection with neuromuscular problems. Even in cases of extensive involvement in some neuro-muscular conditions, the back extensor muscles are often spared.

An individual should be able to raise the trunk backward from a face-lying position to the extent that range of motion of the back permits. If a person does not have the strength to perform this movement, and if there is no contraindication, then the back-extension exercises would be appropriate. Adequate strength in back muscles is important for maintenance of upright posture.

When there is severe involvement, a support is necessary. The type, rigidity, and length of the support depend upon the severity of the weakness. Entire trunk musculature is usually involve if Erector spinae are weak. The collapse of the trunk takes place anteroposteriorly and laterally.

Exercise to build up strength in extensors must be gauged according to the patient's tolerance and response. Good alignment must be preserved in recumbent positions, and supports must be provided in sitting or standing positions to help maintain any benefits from exercises.

The firmness of a mattress is an important lactor in the consideration of posture in the lying position. A good sleeping position involves having the various parts of the body in about the same horizontal plane. Either sagging springs or too soft a mattress may permit poor body alignment.

Many people who have experienced postural back pain have found that pain has decreased or been eliminated by changing from a sagging to a firm level bed Others who have been accustomed to sleeping on a firm mattress have found that acute pain may be brought on by sleeping on a soft or sagging bed. A pillow under the waist when sleeping on the abdomen, or between the knees in a side-lying position can assist in maintaining more normal alignment and relieve stress on the back.

For some individuals, particularly those who have fixed structural faults of alignment such as exaggerated curves of the spine, a softer mattress may be necessary for sleeping comfort because the mattress will give mote support and comfort if it conforms to the curves than if it "bridges" them.

An adult might be comfortable without a pillow when sleeping on the back or abdomen, but would probably not be comfortable in a side-lying position. Use of too high a pillow or more man one pillow may contribute to faulty head and shoulder positions. However, a person who is used to sleeping with the head high should net change abruptly to using a low pillow or none at all. A person who has a fixed postural fault of forward head and round upper back should not sleep without a pillow. It is important to have a pillow high enough to compensate for the round upper back and forward head position. Without a pillow or if the pillow is too low, the head will drop back in hyperextension of the neck.


Respiration refers to the exchange of gases between the cells of an organism and the external environment. Numerous neural, chemical and muscular components are involved. This section, however, relates specifically to the role of the muscles.

Respiration consists of ventilation and circulation. Ventilation is the movement of gases into and out of the lungs; circulation is the transport of these gases to the tissues. Although the movement of gases in the lungs and tissues is by diffusion, their transport to and from the environment and throughout the body requires work by the respiratory and cardiac pumps.

The respiratory pump is comprised of the muscles of respiration and the thorax, which in turn is made up of the ribs, scapulae, clavicle, sternum and thoracic spine. This musculoskeletal pump provides the necessary pressure gradients to move gases into and out of the lungs to ensure adequate diffusion of oxygen and carbon dioxide within the lung.

The work of breathing performed by respiratory muscles in overcoming lung, chest wall, and airway resistances normally occurs only during inspiration. Muscular effort is required to enlarge the thoracic cavity and lower the intrathoracic pressure. Expiration results from the elastic recoil of the lungs on relaxation of the inspi-ratory muscles. The muscles of expiration are active, however, when the demands of breathing are increased. Heavy work, exercise, blowing, coughing, and singing all involve significant work by the expiratory muscles. Also, in conditions like emphysema, in which the elastic recoil is impaired, techniques such as pursed-lip breathing are employed to enhance expiration and minimize effort.

The Respiratory Muscle Chart on page 239 shows the division of muscles according to their major inspira-tory or expiratory roles in ventilation. This division, however, does not mean that the listed muscles function only in that singular capacity. For example, abdominal muscles, which are the chief expiratory muscles, also play a role in inspiration. The inspiratory intercostals as well as the diaphragm also perform an important "braking" action during expiration.

The further division on the chart into primary and accessory muscles shows the numerous muscles that can be recruited to assist in the ventilatory process. Exactly which muscles participate as well as the extent of their participation depends not only on the demands of breathing but also on individual differences in breathing habits or needs.

The fact that breathing can be altered by changes in position, emotional state, activity level, disease, and even the wearing of tight garments means that numerous variations in patterns of breathing exist. For example, Duchenne remarked that normal breathing of women in the mid-19th century was "of the costosuperior type" because of compression from corsets on the lower part of the chest (33).

According to Shneerson, "It is better to regard the respiratory muscles as being capable of recruitment according to the pattern of ventilation, posture, wakefulness or stage of sleep, muscle strength, air flow resistance, and compliance of the lungs and chest wall" (34).

Some authorities dispute the accessory role of certain muscles, particularly the upper trapezius and serra-tus anterior. Other muscles also often are omitted in writings about the accessory respiratory muscles. The rhomboid, for example, which is not included in the accompanying Respiratory Muscle Chart, has a role in stabilizing the scapula to assist the serratus in forced inspiration.

All the muscles listed on the chart have the capacity to be recruited, when needed, to facilitate breathing. Many of them perform vital roles in stabilizing parts of the body so that adequate force is provided to move air both into and out of the lungs. As the work of breathing increases, larger volumes of gas must be moved more quickly, and greater pressure generation is required. The ventilatory muscles work harder, and additional muscles are recruited to meet the demands of breathing.

The following quotation emphasizes the importance of all respiratory muscles: "The distance runner struggling for air .. . may use even the platysma for expanding his chest, and the patient in paroxysms of cough probably contracts every muscle of the trunk, thorax and pectoral girdle during forced expiration" (35). Although the numerous muscles of the upper airways, especially the intrinsic and extrinsic muscles of the larynx, are not discussed here, they play an important role in permitting the free flow of air both to and from the lungs. (See p. 139 for laryngeal muscles.)

In some individuals and under certain circumstances, accessory muscles may be used as the primary muscles. If the diaphragm or intercostals are paralyzed, for example, breathing is still possible through increased use of the accessory muscles. The importance of the accessory muscles was well documented in the case of a patient with a permanent tracheostomy and no movement in his diaphragm or intercostals muscles. He had, surprisingly, a very large vital capacity, breathing with scaleni supplied by the cervical nerves and with the ster-nocleidomastoid and upper trapezius supplied by the spinal accessory nerve (36).

A variety of techniques, procedures, and mechanical devices are used to assist lung function. Treatment must be specific to the ventilatory problem of the patient, but certain principles and practices are basic to all respiratory therapy.

Reduce Fear: The first step in reducing the work of breathing and instituting effective treatment is to reduce the patient's level of fear and anxiety in order to obtain confidence and compliance. Existing respiratory problems are severely exacerbated by breath-holding, breathlessness, and increased tension in the accessory muscles, all of which frequently accompany a fearful state. When the confidence and cooperation of the patient are obtained, other treatment measures will be far more effective.

Improve Relaxation: Relaxation produces a decrease in oxygen consumption of the skeletal muscles and an increase in compliance of the chest wall. When indicated, diaphragmatic breathing exercises may aid in relaxation and give die patient a better sense of control over respiration. These exercises emphasize abdominal rather than rib cage expansion, and they are helpful in cases with overuse of the accessory muscles of the neck and upper chest Practicing a pattern of deep breathing and sighing can reduce the work of breathing and help to relax a patient who has attacks of breathlessness or breath-holding.

Improve Posture: Optimal breathing capability derives from a posture of optimal muscle balance. A balanced musculature is most efficient in terms of energy expenditure.

Imbalance of the musculature resulting from tightness, weakness, or paralysis may adversely affect the volumes and pressures that can be attained and maintained. Very weak and protruding abdominal muscles are not able to generate maximum expiratory pressures to meet increased demands of breathing brought on by exertion or illness. Weakness of the upper back erector spinae and of the middle and lower trapezius muscles interferes with the ability to straighten the upper back, limiting the ability to raise and expand the chest and thus maximize lung capacity. Postural problems associated with kyphosis, kyphoscoliosis, osteoporosis, and pectus excavum restrict breathing and result in decreased chest wall compliance.

Improve Strength and Endurance of Respiratory Muscles: "Strength is needed for sudden respiratory movements such as coughing and sneezing, and brief spells of extreme exertion, whereas endurance is necessary for more prolonged exercise or to overcome an increase in air flow resistance or a decrease in compliance" (34).

Strong and well-conditioned muscles are more efficient and require less oxygen for a given amount of work than poorly conditioned muscles. Reports are mixed as to the efficacy of muscle strength training of respiratory muscles, but such training may be beneficial if respiratory muscle weakness limits exercise or diminishes inspiratory capacity.

The stronger the abdominal muscles, the greater their ability to compress the abdomen and thus generate additional pressure during expiration. Exercises to strengthen these muscles can help to improve coughing and other expulsive maneuvers that are required to clear the airways and facilitate breathing.

If there is marked weakness of these abdominal muscles, exercises should be supplemented with a support that will reduce the downward pull of the abdomen and help to keep the diaphragm in the most advantageous position for both inspiration and expiration. Such assistance often helps to minimize breathing problems associated with obesity.

Respiratory muscle fatigue may precipitate respiratory failure. Endurance training is intended to increase the capacity of muscles to resist fatigue. Training has been shown to benefit approximately 40% of patients suffering from chronic air-flow obstruction, and slight improvements in endurance have been observed in patients with cystic fibrosis (34).

In disorders of the respiratory muscles, "[respiratory failure is usually closely related to the degree of respiratory muscle weakness but occasionally occurs with only mild impairment of muscle function" (34). Because of the high risk of respiratory failure associated with weak respiratory muscles, exercises to strengthen these muscles may be of critical importance, but they also must be very conservative and closely monitored.

Improve Coordination: The oxygen cost of performing a task can be greater than normal in a person who moves in an uncoordinated fashion. When inefficient patterns of breathing and movement are identified, corrective treatment can be instituted, and the work of breathing will be gradually reduced.

Improve Overall Fitness: Cardiovascular fitness can be improved through whole-body exercises (e.g., walking and bicycling) to strengthen ventilatory capability and efficiency. Exercises that involve the legs rather than the arms are preferred initially so that the accessory muscles can be used to aid breathing.

Reduce Weight: Respiratory problems associated with obesity often are very severe. According to Cherniack. the oxygen cost of breathing in an obese person is approximately threefold the normal cost (37). Unlike some skeletal and neuromuscular respiratory disorders, obesity is a condition that can sometimes be reversed, with, in turn, respiration greatly improved.

Of the more than 20 primary and accessory muscles shown on the Respiratory Muscle Chart, almost all have a postural function. Only the diaphragm and the anterior intercostals may be purely respiratory. Twenty of these muscles have either all or part of their origins or insertions on the ribs or costal cartilages. Any muscle attached to the rib cage is able to influence the mechanics of breathing to some degree. These muscles must be able to help support the skeletal structures of the venti-latory pump and to generate pressures that ensure continued adequate gas exchange at the alveoli.

These pressures can be substantial. To double air flow, a fourfold increase in pressure normally is required. If air flow is to remain constant in the face of a twofold decrease in the radius of an airway, there must be a 16-fold increase in pressure (35).

Respiratory complications can arise from a variety of obstructive and restrictive diseases as well as neuro-muscular and skeletal disorders. Once a diagnosis is established, treatment is designed to preserve the existing lung function and to eliminate or reduce the problem that is compromising respiration. The goal is to improve a patient's ability to ventilate the lungs.

Of primary importance is the need to lessen the work of breathing and thus reduce the energy expenditure (i.e., oxygen consumption) of the respiratory muscles. Depending on the respiratory disorder, it may be the elastic, resistive, mechanical, or some combination of such work that needs to be alleviated. Respiratory failure can result when the increased work of breathing leads to alveolar hypoventilation and hypoxia.


The diaphragm (see p. 236), by virtue of its attachment and actions, serves as a pressure partitioner and force transmitter. Normal length and strength of this muscle are essential for these functions. Limited or excessive excursion of the diaphragm reduces its effectiveness in both inspiration and expiration.

In certain respiratory conditions (e.g., emphysema), the diaphragm is not able to return to a dome-shaped contour on relaxation; rather, it is held in a shortened, flattened position. Both pressure-generating capability and inspiratory capacity are reduced, because the lungs


remain in a partially inflated state at the resting level. Also, the ability of the diaphragm to act as a force transmitter and to assist in emptying the lungs is reduced.

The abdominal viscera, supported by the abdominal muscles, normally limit the downward descent of the diaphragm during inspiration and assist with its upward movement during expiration. Under abnormal circumstances, mere can even be a reverse action of the diaphragm. A dramatic example was seen in an infant with poliomyelitis who was placed in a respirator. The muscles of the abdomen, which normally are weak in infants, were paralyzed. During the positive-pressure phase, air was forced out of the lungs, and the diaphragm moved upward. During the negative-pressure phase, air was drawn into the lungs with a momentary expansion of the rib cage, followed by excessive descent of the diaphragm into the abdominal cavity. The abdomen ballooned as the viscera moved downward. By virtue of the attachment of the diaphragm to the inner wall of the chest, the ribs were drawn downward and inward, causing the rib cage to "cave in" as the diaphragm descended into the abdominal cavity— completely defeating the function of this muscle. Within hours, a support in the form of a tiny corset was made and applied to restrict the ballooning of the abdomen and help to prevent the excessive descent of the diaphragm and the devastating effect of this on the rib cage.

Aorta Vena cava l'éi

Central tendon

Esophagus opening

Aorta Vena cava

Central tendon

Esophagus opening

Psoas Muscle Throat

Quad lumb Psoas major

Diaphragm, longitudinal view, inner surface of left side

Quad lumb Psoas major

Diaphragm, longitudinal view, inner surface of left side


Origin, Sternal Part: Two fleshy slips from dorsum of the xiphoid process.

Origin, Costal Part: Inner surfaces of the lower six costal cartilages and lower six ribs on either side, inter-digitating with the transversus abdominis.

Origin , Lumbar Part: By two muscular crura from the bodies of the upper lumbar vertebrae and by two fibrous arches on either side, known as the medial and lateral arcuate ligaments, which span from the vertebrae to the transverse processes and from the latter to the 12th rib.

Insertion: Into the central tendon, which is a thin, strong aponeurosis with no bony attachment. Because the anterior muscular fibers of the diaphragm are shorter than the posterior muscular fibers, the central tendon is situated closer to the ventral than to the dorsal part of the thorax.

Action: The dome-shaped diaphragm separates the thoracic and abdominal cavities and is the principal muscle of respiration. During inspiration, the muscle contracts, and the dome descends, increasing the volume and decreasing the pressure of the thoracic cavity while decreasing the volume and increasing the pressure of the abdominal cavity. The descent of the dome or central tendon is limited by the abdominal viscera, and when descent occurs, the central tendon becomes the more fixed portion of the muscle. With continued contraction, the vertical fibers that are attached to the ribs elevate and evert the costal margin. The dimensions of the thorax are constantly enlarged craniocaudally, an-teroposteriorly. and transversely. During expiration, the diaphragm relaxes, and the dome ascends, decreasing the volume and increasing the pressure of the thoracic cavity while increasing the volume and decreasing pressure of the abdominal cavity.

Not©! In cases of pulmonary pathology (e.g., emphysema), the dome of the diaphragm is so depressed that the costal margin or base of the thorax cannot be expanded.

Tests: See pp. 240 through 241.

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