Some Principles Which Underlie Therapeutic Exercise

SOME PRINCIPLES WHICH UNDERLIE THERAPEUTIC EXERCISE EARL C. ELKINS DEFINITION

THERAPEUTIC or corrective exercise may be described as the scientific application of bodily movement in treatment of disease or of malfunction. This definition in some respects does not seem adequate, since in many of the stu~ies on therapeutic exercises, and in the discourses presented on the subject, some of the basic factors involved are disregarded. The physiologic, mechanical and anatomic factors concerned with motion are often minimized whereas the indications, procedures and apparatus necessary are presented in detail. Therefore, the subject is not particularly clear to those who are not especially trained in the use of corrective exercise, because knowledge of the basic factors involved is essential. It would appear, then, that the definition of this subject should be more comprehensive. It should carry the implication that somewhat extensive knowledge is necessary to use adequately exercise or bodily motion for therapeutic purposes. Dorland's definition of the term "kinesiology" reads: "the sum of what is known regarding muscular movement, especially hygienic and therapeutic movements." This definition implies that wide basic knowledge is necessary and, were it not that confusion of terms might result, the definition could be taken to apply to therapeutic exercise. One who accepts the responsibility of supervision of therapeutic exercise should have knowledge of mechanical, biochemical and biologic laws in relation to mechanical efficiency, and knowledge of physiologic and pathologic-physiologic reactions resulting from malfunction. Such an one must give special study to intricate pliysiologic processes in their relation to muscular and bony structures, and consideration to the relationship of malfunction and normal function to organs of the body which otherwise are unaffected. 923

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Several systems of exercise have been developed in the past two centuries. The Turnverein system was introduced in Germany by Ludwig Jahn. Pehr Ling and Adolph Spiess founded the Swedish system ~nd Delsarte, the French. These are the three principal systems of exercise but many other systems have been developed. In the middle of the nineteenth century, American educators and physicians developed a system of gymnastics suitable for use in this country. It has been the tendency in the recent past for most of the exercises performed in colleges to be in the form of sports. However, sports and formal gymnastics are now employed much less than in previous years and corrective exercises for therapeutic purposes are being developed to a greater degree. As has been pointed out by Ewerhardt: 11 "In general the trend today is towards national sport activity, less formal gymnastics and the introduction of corrective gymnastics in the public school systems." However, it is surprising that, in the light of the considerable amount of theoretical study and knowledge of muscular physiology, so little of this basic knowledge is put to actual practice in medicine. In general, the teaching of therapeutic exercise, or kinesiology, has been grossly neglected in regard to its use in the field of medicine. The makers of medical curricula perhaps can be blamed to a certain degree for this neglect. In most medical schools little functional anatomy is taught in relation to the skeletal-muscular mechanism. Usually, also the physiology of muscle is not presented from the standpoint of its general function in regard to motion. Little attempt is made to correlate biophysical and purely physical laws with motion and locomotion. Even though motion is perhaps the most important function of life, and the skeletal-muscular system therefore constitutes an extremely important part of the body, much less time is spent in teaching the function of this system than is spent in teaching the functions of systems of lesser consequence. The use of corrective exercise has been of much greater interest to those practicing physical education and to the militarist than to the average physician. Correlation is lacking among the kinesiologist on the one hand and, on the other, the physiologist, anatomist and practitioner of medicine. Much of the investigative work has been done by people interested only in one field, such as physical education or physiology of muscle. Study of normal and pathologic motion would seem to be of extreme importance, and probably will become of greater importance, in relation to physicians as time goes on. This is particularly true at present, with the likelihood that a great deal of rehabilitation soon will be necessary. Even if there were no war, increased use of the automobile and increased industrialization of life have resulted

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. and will result, in many injuries affecting locomotion of man. Great benefit might result from more interest in, and wider knowledge of the basic principles of corrective exercise. The purpose of this discussion, therefore, is to present a few of these principles which seem to be basic, some of which are well known but little used from a practical standpoint. BASIC PRINCIPLES INVOLVED IN MUSCULAR ACTION

Muscles are useful only because they are able to produce motion through tension between their various attachments. Therefore, two general factors exist in regard to muscular physiology. One is the mechanism by which muscle fibers are able to produce tension; the other is the means by which muscular tension is applied in order to perform satisfactory motion. Muscular power would be of no value unless the means were present by which this tension could become effective in the organism. Thus the two factors are interdependent and will be discussed together. The Bones as Levers

Muscular tension is made useful through the action of this tension on a series of levers provided by the rigid skeletal structures. The ability to increase the power of applied force is the main function of the series of levers. However, in the body the levers not only increase the power but, probably of more importance, they produce rotation. This is essential because locomotion of a jointed body is produced by rotary forces. Also, most motions of the body other than locomotion are dependent on rotary forces as well as actual power. Many influences affect the lever system, such as gravitational forces, forces of acceleration and deceleration and the external forces related to gravity that are necessary to maintain equilibrium. Regulation of motion must take place through muscular action. This is done in three ways: Hl "( 1). When movement is not desirable, the muscles must exert force which will balance the other forces present, so that rotation of levers does not take place. (2). When movement does take place, the muscles must be fible not only to accelerate movement, but also to decelerate movements. (3). Muscles must be able to regulate the energy of the system by contributing energy from the chemical forces or removing energy by dissipation into heat as occasion requires." .

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Three orders of levers are considered to exist in the human bodily mechanism. The lever of the first order is that in which the fulcrum lies between the weight (resistance to be overcome) and the power (muscular action) as in the point of insertion. An example of this lever in action is extension of the head. The power is produced by the extensor muscles of the head, the fulcrum is at the middle of the atlanto-occipital joint and the weight lifted is the head. Another example is offered by the triceps muscle and the elbow joint when the arm is in the position of abduction and inward rotation. The triceps provides the power; the distal end of the humerus is the fulcrum and the forearm and hand which are being extended constitute the weight. The lever of the second order is one in which the weight lies between the power and the fulcrum. An example of that lever in action is the act of rising on the toes. The toes are the fulcrum, the weight is on the tibia in the ankle joint and the Achilles tendon produces the power. The third order of levers IS one in which the power is applied at some point lying between the fulcrum and the weight. An example of this is to be found in the action of the biceps brachii on flexion of the forearm. The weight is the forearm and hand, the fulcrum is at the elbow and the power is at the insertion of the brachialis tendon on the ulna just below the elbow. These levers impart visible motion to the skeleton through rotary components. Stabilization of Joints Another important function of muscular action is that of stabilization of the joints, or the so-called invisible motions. Stabilization is dependent on the fact that the muscles are so attached that they produce a pull almost parallel with the long axis of the bones. This produces a strong component of force in this direction, which tightens the joint capsule and pulls the articular surfaces together, giving much greater stability of joints. These invisible motions are produced before actual rotary motion takes place; they will be discussed further under maintenance of balance. It has been pointed out by Steindler22 that stabilization is a static function of motor power and is as important as if not more important than, the rotary action of muscular pull. Subluxation of joints would occur and many more strains and stresses would be present in the joints if such stabilizing action were not present. Deformities are brought about by lack of such action in certain cases of muscular paralysis and weakness. Examples of this are subluxation of the humerus in the presence of paralysis of the deltoid muscle,

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"back knee" deformity in cases of paralysis of the quadriceps muscle and deformities of the feet which occur when the muscles which support the arches of the feet are weak. Increasing the Angle of Pull

Another topographic adaptation is an important element in relation to muscular action. In nearly every instance, the muscles are almost parallel to the axis of the bones to which they are attached. Therefore, certain provisions are made for increasing the angle of pull and thereby the rotary action. If these factors were not present, the parallel axis of pull would, in some instances, produce a "dead center" and would interfere with rotary motion. Examples of such adaptation are the ballshaped ends of bones, which cause deflection of tendons away from the joints, thus producing a greater rotary component of pull. Specific examples are the following: (1) The gastrocnemius and the hamstring muscles are deflected away from the knee joint by the prominent ball-like surface of the condyle of the femur. (2) The quadriceps muscle is attached in the patella; thus the patella deflects the tendon away from the knee joint, giving the muscle a greater rotary force. In the fingers, the tendons of the flexor digitorum profundus and of the flexor digitorum sublimis run almost parallel to the bones, but the attachment of the flexor digitorum sublimis is divided at the base of the proximal phalanx of each of four fingers. The tendons of the flexor digitorum profundus run to the distal phalanges of the fingers, having passed through the tendons of the flexor digitorum sublimis muscle. When the flexor digitorum sublimis contracts, the tendons of the flexor digitorum profundus are pulled away from the bones, thereby giving the tendons greater rotary force on the distal phalanges of the fingers. Elasticity and Extensibility

These are considered important physical properties of muscles. The elasticity of muscles follows Hooke's Law to a certain degree; that is, -muscles increase in length in direct proportion to, the extending force. Extensibility of a muscle means that, when it is placed on stretch, it is capable of being extended. Elasticity and extensibility of muscle are essential for several reasons; namely, they allow smoothness of motion; they tend to relieve the sudden impact consequent on overcoming the

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inertia of load, and thus they allow greater tension, which increases the power of muscle and prevents rupture. The point at which rupture of muscle will occur has not been fully investigated. However, it is known that long before the breaking point has been reached, the extending force will cause structural damage. It also is known that persistent stretching of a muscle will produce fibrous degeneration and that sudden stretching may tear individual muscle fibers. Therefore, sudden, forced motion should be avoided in doing therapeutic exercise. Careful appraisal of elasticity and extensibility should be made of muscles under treatment. It should be kept in mind that decreased extensibility and elasticity do occur and that there are limitations beyond which muscles cannot be stretched safely. It is considered better technic to attempt to increase the power of the muscle that opposes the shortened or spastic muscle and to use this muscle to produce active stretching of ,'the involved muscle. This decreases the possibility of producing muscular spasm, tears and possibly the permanent damage that sometimes results from forced, passive stretching. Contractility

The contractility of muscles is a complex phenomenon and space does not allow of detailed discussion here. However, it has been known for centuries that the lifting height of muscles is greater, the greater the length of the fibers. The ability of muscle to lengthen has been variously estimated and, in general, it is known that there is a great deal of difference in the contraction length of fibers of the same muscle. A muscular contraction is most powerful when the muscle is at its maximal length, since its tension is greatest in this position. Tension becomes markedly reduced as contraction progresses. Thus, the power of muscle is greatly decreased when it is most fully contracted and shortened. When partial contraction of a muscle has given it increased power through increased leverage, this gain is offset by the loss of tension. In performing re-education exercises or in testing for strength of a muscle, it is desirable to place the muscle in a situation wherein its full power or greatest strength can be ascertained. There are two methods by which this can be done. First, the angle of pull can be increased by flexion of the joint which is moved by the muscle. This releases tension, but increases

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leverage. To state the reverse of the point of view expressed at the close of the preceding paragraph, the loss of power occasioned by decrease of tension is compensated by the flexion. Sometimes, a second joint which the muscle crosses can be extended in order to increase the tertsion lost by flexion of the first joint. An example of this is the movement of the leg on the knee. The hamstring muscles are at a greater advantage in lever~ age when the knee is partially flexed. If the knee alone is flexed, these muscles lose tension and thereby power. If the hip is flexed, then the hamstrings are put under tension and the advantage both of increased leverage and of tension are obtained. This mechanism comes into play primarily in respect to muscles which serve more than one joint, and is of considerable importance whenever rehabilitation of such muscles is attempted. These so-called pluri-articular muscles will be considered again when coordination is discussed. Mono-articular muscles are exercised usually in their resting length. The degree of muscular tension is governed by the degree of innervation. IS. 22 The inhibitory centers tone down the state of contraction to an optimum which changes with the dynamic requirements. Until comparatively recent times, not much information could be obtained as to how much innervation was necessary to each muscular contraction. However, this has been studied to a certain extent since it has been possible to measure the action current. 22 It is known that graded responses are brought about by varying the number of muscle fibers, or the units of the muscles, which are involved in response at anyone time.1S The studies of Adrian and Bronkl indicated that the rate of discharge of impulses from the central nervous system is highly variable in voluntary contractions. Not infrequently contractions began at a stimulation rate of five or six per second, but gradually increased in magnitude as the contractions became stronger. They ultimately reached a rate of thirty and forty per second, sometimes as high as fifty per second in powerful responses. Therefore, graduation of response is effected by variation in the rate of discharge of impulses from the central nervous system. Numerous investigators have shown that more energy is required to' accomplish a given task rapidly than to do it slowly. The primary reason for this lies in the fact that there is intrinsic as well as extrinsic muscular resistance. This intrinsic resistance of muscle l6 to contraction is due to structural arrangement. Two factors are present. One is the viscous fluid which surrounds the muscle fibers.

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When muscle fibers shorten they must expand and the viscous fluid tends to occupy the space needed for expansion. The other factor is assumed to be the passive resistance offered by the fibers in the muscle which are not used in the contraction (it is unusual for all fibers of a muscle to be in a state of contraction at one time). These unused fibers are shortened passively and impede the fibers which are contracting. This internal resistance, present in the muscle during contraction, supposedly tends to prevent too rapid contraction. By too rapid contraction the muscle might tear itself apart. As compared with slow motion, rapid motion uses a great deal more energy to accomplish much less work. Most muscular action is done at a certain optimal rate at which it can accomplish the most without fatigue. Undoubtedly, this optimal rate varies with the condition of muscular power and with the neuromotor elements which control it.

From the standpoint of clinical application, exercise should be taken or given slowly in nearly all instances, because (1) if innervation is poor, only a few muscle fibers may be activated and fatigue will appear quickly even with slow motion, but rapid movement further increases the possibility of fatigue; (2) in muscles weakened from causes other than lesions of the nervous system, slow, mild motion should be used gradually to strengthen the muscle. Rapid, maximal motion quickly fatigues muscle and may be harmful owing to inability of the muscle to recover from the chemical products of fatigue. In certain conditions such as those in which there is articular involvement (inflammatory or traumatic) other factors, aside from those involving the muscle, must be taken into consideration in relation to speed and intensity of motion. Sudden, jerky or rapid movements in these instances tend to produce more damage or trauma to already involved joints, which in turn produce more muscular spasm and loss of muscular power, elasticity and contractility. Thus a vicious cycle results. Tone

Muscular tone is the quality whereby muscle remains under sustained tension. Tension is necessary to maximal power of muscular contraction. Tone is necessary. to maximal efficiency of the contraction and, therefore, tone is important in relation to economy of energy. Likewise, tone is of importance with respect to adequate stabilization of the skeletal system.

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It is known that complete muscular relaxation does not occur during life except under deep anesthesia. The state of muscular tension which is maintained somewhere between complete relaxation and contraction is known as simple tone. This tension increases during waking hours. It also varies with physical and mental activity. Tone is not inhere nt in muscle but is dependent on reflex arcs and other connections with the central nervous system. When the reflex arc is broken, the muscles involved become completely relaxed. The highly localized monomuscular reflex was described by Sherrington and is given the name "myot atic reflex." Adequate stimulus for this reflex is that of stretching and this stimulus excites proprioceptors in general. When a muscle or a portio n of a muscle is stretched, it responds by a change of tone which is proportional to the strength of the stimulus. This is the stretch reflex which is well known. The mechanism of tone is not well known. However, muscular tone can be maintained actively over long periods withou t fatigue. From a clinical standpoint, the importance of maintaining muscular tone has been long recognized. Lack of tone in muscles can be responsible for loss of tension and reduced power, although tone is not identical with power. Occasionally, because of lack of tone, a fairly strong muscle is not adequate to 18 the task of holding a limb in a given position. Lack of tone may add to the instability of joints and may increase the chances of injury or sprain, because muscles are as important as ligaments and other joint structures in stabilization of joints. Theref ore, increased length. and relaxation of muscles, throug h loss of tone and tension may affect materially this stabilization of joints. Exercise can be used to increase the tone of muscles. Such exercise should be of the isometric type, that is; a tightening of joint the muscle withou t producing motion, or a holding of the 18 ce. resistan against n positio given a and its movable part in Jacobson 17 has done much to prove the importance of the ability to relax. There is evidence that increased tone or a "tension state" does exist and that it may be of greater impo}."tance in our every day living than once was considered. Coordination

Coordination of muscular action is complicated not only from a musculoneural standpoint, which will not be discussed to any

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extent here, but also from a mechanical standpoint. In relation to the neuromuscular mechanism, it must be pointed out that in order to have coordination and smoothness of motion, the reflex arcs must be intact. "The maintenance of posture is an example of the nicety of adjustment between various parts of the body to fit the new position--." Reciprocal innervation and inhibition of muscles are most important in producing coordination. Reciprocal innervation means that when a voluntary or reflex contraction occur, as in the biceps muscle, it is accompanied by relaxation of its antagonist, the triceps muscle. 4 The inhibition is not brought about through specific inhibiting nerves as are cardiac and intestinal inhibitions, but is due to cessation of excitations and impulses along the motor neurons. 4 The mechanical elements entering into coordination are not often stressed. However, as has been pointed out aptly by Steindler,22 considering coordination from a mechanical standpoint, elementary knowledge of the lever system and, one might add, of neurologic control, does not suffice. It is necessary to consider not only the effect of muscle on its own lever arm, but also on neighboring and even remote articulations. The stresses, strains and resistances due to gravity and inertia must be taken into consideration as they affect tension and rotary motion. Complicated problems arise in relation to action of the pluri-articular muscles and their effect on more than one articulation. The meaning of the functional efficiency of a pluri-articular muscle can be grasped only when the action and reaction of the whole limb or body as a mechanical unit are taken into consideration. Only fairly recently has the plural action of single muscles been considered. Most books on anatomy give only one principal action of a muscle. But "there is hardly any muscle which has an unchangeable motor effect in respect to any joint and it will appear consistently . . . that muscle function changes constantly with the position of the muscle in relation to the three orientation planes. As the function of the muscle changes, so changes also that [the function] of the antagonist, being never quite the same in different positions; and this change is both qualitative and quantitative...."22 In numerous instances the primary function of a muscle in respect to a certain plane gradually changes to the reversed motor effect. The mechanical variations and multiple actions of muscles

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relative to coordination cannot be discussed in their entirety in a paper of this type. However, certain characteristics relative to these variations and actions, which may be of clinical value, and which might create greater interest in further observation, will be mentioned. Several types of contraction relative to muscular function should be reviewed. When contraction of a muscle produces decrease in distance between its origin and insertion, this is known as a "shortening contraction" or a "concentric contraction." This type of contraction overcomes gravity or resistance and produces motion. During this contraction, either both ends of the muscle will move toward each other or, if one attachment of the muscle is fixed, the other attachment will be moved. This action then can have various effects. The origin of a muscle can be moved or, reversing the movements of the parts, its insertion can be moved. Examples of this action can be· seen in relation to the anterior tibial muscle. When the origin of this muscle (the tibia) is fixed, the foot is moved in relation to the leg. If the foot is stabilized, as it is when a person is standing, the leg is moved or stabilized. Again, the gastrocnemius may bring about plantar flexion of the foot or, if the foot is fixed, action of the muscle is on its origin (the femur) and the tendency is to flexion of the thigh. Another type of contraction is known as eccentric or lengthening contraction. In this type of contraction outside forces cause the movement and the muscle regulate the speed at which the outside force may move the part. The muscular force constitutes a braking action. An example would be that of the flexed forearm being pulled down by the weight of the forearm and hand. The triceps does not act at all to produce extension, but the biceps brachii increases its length while, nevertheless, braking the speed of movement. This action is of considerable significance in coordination and in regulation of speed of a movement in which the part already in motion may exert considerable momentum. If a muscle acts "to take up slack," but produces no motion, the action is known as a "static contraction" and is primarily stabilizing in its effect. Other examples of such action are numerous in the coordinated muscular movement of the body; for instance, the stabilizing contraction of the gluteus muscles to prevent pelvic tilt in the process of taking a step, or contraction of the extensor muscles of the wrist in order to stabilize the hand when flexion of the fingers occurs. Another muscular action which is of importance in relation to coordination is that known as "guiding action." During this action,

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muscle does not actually perfonn motion but controls the direction of motion. An example of this is the following: When the gastrocnemius and soleus muscles bring about plantar flexion of the foot, the tibialis anterior and the peroneal muscles guide the inversion and eversion. It is obvious that there are many other instances of such action of muscle. These muscles which exert guiding action are in fine balance with each other and with the prime movers in regard to direction. Another action of muscles is that necessary for maintenance of balance. This has to do with action around weight-bearing joints. Essentially, it consists of a give-and-take action, in which minute eccentric and concentric contractions of muscles restore balance when imbalance begins or has occurred. 7 These minute contractions control the invisible motions that were maintained in the discussion of stabilization. As already has become evident, there are two general groups of muscles in the body relative to the joints: the pluri-articular muscles and the mono-articular muscles. In general, these groups act similarly in relation to the several actions of muscles, that is; they act concentrically, eccentrically or static ally. Any of them may produce a stabilizing action, may assist in balancing or may exert a guiding action. Pluri-articular muscles become important as economizers of energy, especially in relation to the synergistic action of mono-articular muscles. The more joints a pluri-articular muscle covers, the more the possibilities of its action there may be. Theoretically, when a muscle passes over several joints, it may act on anyone of the joints or on all of them, or on any combination of joints. Therefore, it cannot properly be said that a pluri-articular muscle has a primary action and secondarily produces other definite actions. These so-called secondary actions will depend on the circumstances at the time of the motion in relation to the gravitational pull, the rotational components and the various parts of the body which may be fixed. Examples can be cited, such as when the biceps brachii contracts if the shoulder is fixed. The elbow flexes and, combined with this flexion is forward flexion and abduction of the shoulder. Another example is that in which the pelvis is fixed when one is rising from a sitting position. The ball of the foot is fixed on the ground, the knee slightly flexed, and contraction of the hamstring muscles produces extension of the knee and dorsiflexion of the foot. The concurrent and countercurrent shifts of the bi-articular muscles, as pointed out by Baeyer,2 have been studied particularly in relation to gait. Concurrent shifts of muscles are described as parallel actions between two groups of bi-articular muscles in

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which neither group changes its length. An example of this is when the hip and knee are being flexed at the same time. The hamstring muscles in this instance move in a parallel manner, or concurrently, and in cooperation with the rectus femoris muscle; that is, as the knee flexes with flexion of the hip, the origin of the hamstring muscles moves upward and so does their insertion. Likewise, the origin and insertion of the rectus femoris move in the same direction; that is, they both move downward. None of the muscles under consideration changes in length. Countercurrent shift, on the other hand, is illustrated when the hip is flexed and the knee extended, the origins of the hamstring muscles moved upward, but their insertions, downward, whereas the origin and insertion of the rectus femoris are moving toward each other. The tension of the rectus femoris will be lessened because the origin and insertion have become approximated. Also the hamstring muscles offer resistance to extension of the thigh when flexion of this member has reached 90 degrees or less; this resistance also hinders extension of the knee. It can be seen, therefore, that concurrent actions of these bi-articular muscles are more efficient than countercurrent actions. The action of mono-articular muscles is not as intricate as that of pluri-articular muscles, but, as has been pointed out, they have all the general actions that the pluri-articular muscles have. Monoarticular muscles frequently act in assistance of the pluri-articular muscles; that is, because of certain positions and because of loss of tension such as occurs in countercurrent action of pluri-articular muscles, associated mono-articular muscles may provide added power to finish the required motion. Examples of these combinations are the gastrocnemius with the soleus, the hamstrings with the short head of biceps and the rectus femoris with the vasti. In some instances, a muscle of lesser magnitude, but of greater leverage, may initiate the primary movement of a more powerful muscle. This is seen when. the angle of pull of the powerful muscle is such that at full length it may be near dead center. Examples are the action of the iliopsoas and sartorius muscles. With the hip fully extended, the iliopsoas cannot produce great flexor power because it is inserted too near the long axis of the bone. This gives great stabilizing power but, in order to produce rotary power, the sartorius, with its greater angle of pull, initiates flexion of the thigh. When a small angle of flexion has been produced the iliopsoas, having great shortening power, becomes a powerful flexor of the hip. This explains why, in the absence of part of the flexors of the hip, particularly of the sartorius, the iliopsoas does not work well even though seemingly it is powerful and even if the hip is extended so that the iliopsoas is stretched.

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Only a few of the intricacies of the mechanics of muscular action and coordination have been cited. Perhaps sufficient material has been presented, however, to indicate the necessity of considerable study of this subject by the physician and technician. ELECTROPHYSIOLOGY

The study of electrical potential created in muscles during their contraction has been carried on to a certain extent since 1918. In this year, Einthoven demonstrated the existence of action currents in muscle. Knowledge of electrical phenomena in relation to nerves and muscles as applied to clinical practice has increased in the past few years. In cardiology, important clinical use is made of the electromotive action of cardiac muscle, as recorded by the electrocardiograph. Likewise, the electro-encephalograph records certain electrical phenomena of the brain and thus aids in diagnosis of certain lesions of the brain. These are indications that study of the electromotive activity of voluntary. muscle might be of considerable value, both from the standpoint of clinical application and from that of investigation of coordinated function of muscle. Currents set up during contraction of muscle have been studied to some extent to determine muscular action. It is obvious that much more knowledge is necessary concerning action of muscle than that obtained purely from the mechanical viewpoint. Currents of low voltage have been used for many years for therapeutic and diagnostic purposes. Even though physiologists have known a good deal about the effect of these currents, not a great deal of what is known has been applied clinically.14 This lack of application apparently is due to the fact that much of the experimental work has been done on animals and, in some instances, it has been due to ideas derived from the work of a few investigators and clinicians of several generations ago, handed down to the present, but possibly not substantiated in the light of present advancement in experimental work. The electrophysiology of muscle is mentioned only in an attempt to point out that this field is undoubtedly of extreme importance in the study of locomotion. It may prove to be important from the standpoint of study of muscular function in relation to mechanics of muscular action; from the standpoint of development of great diagnostic skill in relation to muscular

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disability, and from the standpoint of study and prognostication of certain pathologic lesions affecting voluntary nerves and muscles. PHYSICAL PRINCIPLES AS A BASIS OF GENERAL POSTURE AND LOCOMOTION

It is not within the scope of this paper to discuss fully the maintenance of general posture and locomotion. However, a few aspects of this subject will be mentioned. The physician usually is not so trained as to be greatly concerned with the laws of mechanics in relation to motion. However, these physical laws are just as much in operation in human locomotion as they are in the self-propelled airplane or motor car. Definite stresses and strains result from various forces which are no less exact than those which were exerted on the Golden Gate Bridge. These physical elements have not been determined in all instances in relation to motion of man, but recently much has been learned in this respect. It seems necessary to point out constantly to the physician that many of the malfunctions of motion in human beings might be considered from the standpoint of physics rather than from the standpoint of biology only. That the American public apparently has not been particularly conscious of postural defects has been obvious to European gymnasts. Considering the statistical evidence in regard to postural deformities among the youths of this country, which is being made available from records of examinations for the army, it seems strange that more people have not become interested in good posture. Perhaps it can be argued, however, that since the health of the people of the United States is better than that of the people of any other nation in the world, postural defects are in general of no great significance. Nutrition and environment have an influence on general posture and, recently, more has been said concerning the correlation of the health of the nation and nutrition. Obviously improper nutrition may have an early effect on bodily structures that are of major importance in motion. Therefore, the skeletal-muscular structures of that large group of people who do not have adequate or proper diet may be such that mechanical malfunction may occur or may tend to occur. Furthermore, malnourished persons, including those whose poor posture is due to poor nutrition, usually come from that large part of the population which does not receive higher education. Until recently, postural training, as such, was not taught in primary and

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secondary schools and persons of primary and secondary school age scarcely can have acquired the background which would enable them to understand nutritional problems. These matters are taught in college. Yet, the college-trained person actually may need less training in body building from the standpoint of his occupation. He may never do work which would require great muscular effort or which might induce added malfunction from a postural or mechanical standpoint. On the other hand, the person who does not have 3 higher education is likely to do heavier labor. He may be subjected to many factors which may enhance postural and mechanical dysfunction. Yet he is likely to have had little or no training in respect to proper bodily alignment. The point to be made is that more interest and study should be devoted to the effect of posture on general health. The subject should not be left entirely to those in charge of physical education but the physician should be the guide. He can recognize the possible frequent but remote causes of poor bodily mechanics. Remote Stresses and Strains

That poor posture and malalignment may produce remote dysfunction of the body has not received much attention. Only within the last forty or fifty years have physicians been concerned even remotely with posture. If Goldthwait, Brown, Swaim and Kuhns are taken as authorities, it can be assumed that many organic conditions, even some well established entities, may arise from certain stresses aI?-d strains resulting from poor posture. The laws of gravity become of considerable significance in human locomotion when center of gravity, transitory movements and rotary movements are considered. The center of gravity in man has been raised considerably above that found in the quadruped. In order to assume an upright position such as man has, greater extension of the hip than that possible to the quadruped must be available, and the extensor muscles of the spinal column, hip, knees and ankles must be stronger. This is a great evolutionary advance but it has been attended by many factors which may cause added stress and strain and may produce weaknesses. Although the quadruped has greater stability than man, its extremities are articulated so that it still does not have complete stability. As a result of rotary forces, the quadruped would fall if it were not for constant active muscular action and

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equilibrium. Even more in the human body, which is multiarticular, rotary forces are constantly in action on all of the joints to effect stance and motion. The center of gravity of the human being usually is considered to be at the level of the second lumbar vertebra. The line of gravity, which is important in relation to posture, can be determined by various methods.~· 15, 21 It usually runs about 4 cm. in front of the plane of the ankle joints, continues upward just behind the plane of the patellas, then just behind the plane of the greater trochanters of the femurs, in front of the sac rum, intersecting the lumbosacral joint, behind the lumbar portion of the spinal column through the joint between the highest lumbar and the lowest thoracic vertebrae, in front of the thoracic portion of the spinal column through the joint between the highest thoracic and the lowest cervical vertebrae, then behind the cervical vert~brae to the skull. The center of gravity and the lines of force vary with position and motion. The center of gravity, likewise, can be determined in relation to the extremities and the peripheral joints. "The relation of the center of gravity to supporting areas is the principal condition of equilibrium." 22 With loss of equilibrium the person does not fall, but loss of equilibrium is followed immediately by an attempt to regain it. The tendency to fall is prevented by muscular activity. Therefore locomotion can be defined as "a rhythmic play of muscular force between loss and recovery of equilibrium." 22 From the foregoing it can be seen that any element of force or dysfunction that changes the center of gravity and the lines of gravity places many stresses and strains on various groups of m~scles, because then a constant element of disequilibrium remams. The purpose of proper postural alignment is to obtain economy of bodily energy. Anything which constantly displaces the mechanism on which depends increased muscular activity and stress can produce innumerable biological and biophysical disarrangements. These disarrangements may be capab'le of producing many states of tension and thus function may be a.ffected, both biophysically and biologically, in regions remote from that of the stress and strain. Likewise, structural changes may result, not only in the bony framework of the body, but also various soft tissue structures, such as muscles, ligaments and joint capsules, may be stretched or shortened, or both.

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Added to this is the element of fatigue due to overactivity of muscles that are necessary to maintain equilibrium. The weight lines or the gravity lines of the lower extremities and spinal column are of importance in maintaining normal alignment in posture. This is particularly true in relation to the sacrum and the hip joint. As Steindler has said: "The .r~lative position of the pelvis to the trunk and the lower extremitieS has a great deal to do with the intensity of weight stresses in relation to the pelvic junction."22 Steindler further has pointed out four types of posture in which there exist essential deviations in the direction of the weight line, and in the situation of the weight centers relative to the human skeleton. The first type is that in which there is more or less normal inclination of the pelvis, with either a straight or round back. This type is well secured in balance and may be considered normal physiologically. The second type is that in which the weight line is moved forward in relation to the spinal column because there exists a condition such as flexion deformity or inability to extend the hip. Equilibrium is maintained by bending the knees, which carries the supporting surface far enough backward to reestablish the line of gravity. The third type is of very frequent occurrence and is one in which the center of gravity is moved backwards. This is seen in association with various types of paralysis as, for instance, that associated with poliomyelitis, in which the strength of the abdominal muscles is impaired. It is seen also in association with other postural abnormalities in which the abdominal wall is weak and lacks tone. The fourth type is one in which the center of gravity is brought forward by flexion of the trunk. This is seen in cases of osteo-arthritis, senile kyphosis and spondylitis. The rearrangement of the center of gravity in these conditions is compensated for by flexion of the hips and flexion of the knee joints. The essential difference between normal and abnormal posture is that, in normal posture, the spinal column itself, and not the hips and knee joints, makes compensation so that the lines of gravity intersect in the appropriate center. In malposture, on the other hand, apparently the deflected line of gravity persists and results in abnormal relations of this line to the sacro-iliac, hip and knee joints. As was stated by Steindler, normal posture in geometrical terms means compensation for the spinal deflections within the spinal column itself. In abnormal posture,

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the spinal column is deflected in relation to the line of gravity and the deflection is compensated for by the body as a whole through the abnormal position of the pelvis, hip and knees. Stiff or Easy Posture

In the past thirty years, the conception of what constitutes good posture has changed. In 1911, Elin F alk, a Swedish gymnastic instructor, unfavorably criticized the stiff "attention" position commonly used in gymnastics and advocated easy, erect carriage with relaxation of all the muscles which are not directly related to the upright position. This new conception of good posture met with considerable unfavorable criticism in Sweden and a number of years· passed before it was commonly accepted. At present, the so-called "easy posture" has not been entirely recognized as the most efficient means of assuming the upright position. \ Twenty years ago, Bancroft3 pointed out the importance of training the individual to feel the correct posture and emphasized that students should be told "not to try so hard" and to "let go" in order to avoid tension states. Drew9 stated, "the aim of postural exercise is to secure the poise of the body in the proper balance line without muscle tension and rigidity." Rathbone,20 in describing "bodily balance" pointed out the importance of freeing the body from tension. Denniston8 stated, "Good posture for which we strive is not a stiff standing position or military walk but an attitude of ease and grace for every occupation which enables the muscles and levers to work with a minimum expenditure of energy." This same author further spoke of the ability to assume good posture in order "to adjust the body so that it is easily balanced, the segments properly related." However, in innumerable books and articles6 on posture and bodily mechanics exercises are described which do produce increased tension and create additional strain. If the views mentioned are considered to be correct, it must be understood that, in order to have good posture, it is necessary to have proper alignment, proper relationship between the various segments of the body and easy balance. There should be, also, easy grace of movement and minimal expenditure of energy in motion.

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Supra pelvic Structures and Muscles about the Pelvis

In considering the suprapelvic structures and muscles about the pelvis, a large number of separate masses of weight must be recognized. 23 • 24. 25 Each mass has its own center of gravity and its own line of gravity which is influenced by vertical forces. If there is any tendency to tipping of the pelvis forward, backward or sideways, the structures above the pelvis immediately will be thrown out of balance. If these supra pelvic masses are properly aligned with the pelvic bones, it can be assumed theoretically that no muscular effort is required to maintain balance. The nearer proper balance is approached, the less muscular energy must be expended. The muscles around the hip joint function in a standing position to guard the joint against all disturbances. No set of muscles has to contract constantly. There is an interchange of action between the flexors, extensors, abductors and adductors and between the inward and outward rotators. It has long been taught that the way to decrease pelvic inclination is by contracting the gluteal muscles, pulling down posteriorly on the pelvis and upward by means of the abdominal muscles, thereby decreasing the angle of the pelvis. However, as soon as the contracted muscles let go, the force of gravity will increase the inclination of the pelvis. Therefore, as was pointed out by Brunnstrom,6 when the gluteus maximus and the abdominal muscles are used for decreasing pelvic tilt, there is a constant unnecessary expenditure of energy. However, if there is proper alignment of the suprapelvic mass, mainly by seeing that the spinal column is properly erect, much of this excess expenditure of energy will be relieved. It is demonstrated easily that contraction of the gluteus maximus is not necessary while a person is standing; if one stands with the feet pointing straight forward and plac~s the hands over the gluteus maximus muscles, it will be found that they are relaxed. If there is any shift forward or backward, the gluteus maximus muscles immediately come into action but, when the straightstanding position again is assumed, the muscles relax. Also, it seems to be the opinion of most authorities that use of the gluteus maximus is not necessary for ordinary walking, but that it comes into action immediately on climbing stairs, running or jumping. That employment of the gluteus maximus is unnecessary in walking or standing is evident also in certain paralytic conditions. Therefore, this would seem to indicate that use of the gluteus maximus to hold the pelvis in proper position during assumption of good posture is not

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essential and that to use it thus only constitutes a drain on energy. It is believed that the adductor magnus and the hamstring muscles act to bring about decrease in inclination of the pelvis.

In the past, there has been a tendency to pay a great deal of attention to carriage of the shoulders. It is the consensus now that if the shoulders and anns are allowed to hang relaxed, they will assume whatever position the neck and upper part of the back promote, because the shoulder girdle and upper extremities are carried by fascia and muscles which connect the shoulders with the skull, cervical portion of the spinal column and thoracic cage. If the skull and cervical portion of the spinal column are held forward or backward, then the arm or shoulder girdle will hang forward or backward. If the head and cervical portion of the spinal column are well balanced, the shoulder girdle will hang in the proper plane. In cases of contracture of the pectoral muscles, which are the adductors of the shoulder, it has been advocated8 • 26 that they be stretched by active contraction of the retractors of the shoulder. However, this puts tension not only on the middle of the trapezius and on the rhomboids but on all muscles of the shoulder region. The trapezius will contract to effect backward movement of the shoulders and, if emphasis is put on keeping the shoulders low, then the latissimus dorsi and the lower portion of the trapezius will contract. The posterior part of the deltoid muscle and the teres major will increase in tension whether the shoulder is held high or low. However, the aim in cases of contracture of the pectorals is to lengthen them. If this is done by contraction of the retractors of the shoulder, there is set up an undesirable stretch reflex which may enhance the action of the strong pectoral muscles. Moreover, it is unnecessary to use the considerable energy that is necessary to conscious maintenance of contraction of the retractors of the shoulder. The most effective means of lengthening the pectorals is to allow gravity to exert a slight, constant pull on the upper extremity. This can be done by such realignment of the head, thoracic cage and pelvis as will cause the arms to hang in proper position. Obviously this procedure can be used only in those instances wherein there is no condition which will prevent proper alignment of the thorax.

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Reciprocal Shortening and Lengthening

It should be borne in mind that, when malalignment and poor posture occur, usually some muscles are shortened and others are lengthened or stretched. The short, powerful flexor muscles, such as those of the hip, the pectorals and the gastrocnemii usually are opposed by weaker muscles which are elongated. Likewise, the muscles in the lower part of the back may be shortened, while those in the upper region may be lengthened. Therefore, it is essential in examining for poor bodily mechanics or malalignment to ascertain which are the weak groups of muscles, which the overactive groups of muscles, and what malalignment is produced by such muscles. The Feet

A very important field in study of posture has to do with mal alignment of the feet. Many have noticed that a tremendous percentage of people, even from childhood, exhibit malfunction of the feet. Malalignment of the feet has a direct relationship also to alignment of the lower extremities and back and can produce many changes in function of the body as a whole. It has been estimated recently that a high percentage of children aged five years have defects relative to the feet; that at the age of five to ten yeafSl this percentage reaches 45 and, at ten to fifteen years of age, 70 per cent. In view of the fact 40 to 80 per cent of adults in England have defective feet, it can be assumed that a considerable proportion of children in elementary schools have defective or potentially defective feet. 27 Osgood19 recently has pointed out that the normal lines of weight-bearing transmitted through the tibia fall considerably to the medial side of the foot, which condition tends to produce flat feet. Neither the longitudinal arch extending from the calcaneus to the metatarsal heads, nor the anterior transverse arch formed by the heads of the metatarsal bones, have any stability worthy of consideration. Therefore, dependence cannot be placed on the bony configuration to resist the deforming medial and downward force. The muscles that principally tend to maintain proper weight bearing lines relative to the feet are those of the lower part of the leg, which have their insertions in the feet; to a lesser extent the intrinsic muscles of the feet serve the same function. Osgood pointed out that faulty weight-bearing and foot strain are most commonly caused by faulty balance between the group

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of muscles that invert the foot and elevate the arches and the group whose contraction tends to evert the foot and depress the arches. The first group may be called the invertors or maintainers of symptomless weight bearing. If the second group, the evertors, overbalance the first, foot strain usually results. Osgood made a study of the comparative strength in pounds of pull of the two antagonistic groups (the invertors or adductors and the evertors or abductors). He found that in symptomless, normal feet, the invertors, acting as protectors of the arch, were stronger than the evertors or depressors of the arch in the ratio of pulls of 5 to 4 pounds (2.3 to 1.8 kg.). In symptomless feet that exhibited slight pronation, the pull of the two groups of muscles was about equal, or slightly in favor of the evertors. In the presence of more pronation and of symptoms of foot strain, the pull of the evertors was definitely stronger than that of the invertors. In cases of acute fiat foot, the ratio of the pull of the invertors to that of the evertors was about four to five, or the reverse of the ratio existing in normal symptomless feet. Of a group of nurses who were required to stand and walk on harder surfaces and for longer hours than those to which most of them had been accustomed, but who were given corrective exercises, only one who exhibited normal balance at the original examination reported foot strain, and her condition proved to be arthritic and not static; whereas, prior to the use of corrective exercises, an average of one nurse a week was obliged to be off duty because of foot disability. In a further study, made on students of Wellesley College, it was found that faulty balance was of three times more common occurrence than normal balance. Osgood pointed out that normal muscular balance between inversion and eversion should be restored. However, other potential causes of foot strain should not be overlooked. Fatigue, poor muscle tone after illness, unreasonably long hours of standing and walking, unreasonably hard surfaces and improper shoes may be important etiologic factors in producing weak feet. Osgood mentioned that overweight often was blamed but, he said, the muscles usually develop in consonance with gradual increase of weight if activity is maintained. Osgood expressed the belief that foot imbalance could be overcome easily if exercises were persistently followed and precisely performed and that, if an explanation of the cause of a patient's discomfort was made clear and convincing, cooperation could be obtained from most patients. . The weight-bearing lines of the lower extremities are important in regard to foot posture. In the correct position, the weight-bearing line extends from the anterior superior iliac spine, through the middle of the femur and the knee joint and

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comes out just in front of the ankle joint. If extended through the foot, this line would make its exit between the first and second toes. It can be seen readily that if the foot is toed out, this weight bearing line falls well on the inside of the arch, which tends to further pronation and added strain on the longitudinal arch. It can be surmised that pronation and flatfootedness may be increased therefore by walking with the toes turned out and, even though the invertors of the foot may be fairly strong, the added strain produced by this improper position of the foot may weaken these muscles and set up a vicious cycle which promotes more pronation and more flatfootedness. Poor Posture as a Cause and as an Effect of Disease

If disease can cause deviation of proper alignment, and if certain excessive stresses and strains produced by this improper posture can cause remote disorderS in the human body, then this sequence of causes and effects becomes of considerable significance. Correction of posture may be important, not merely from an aesthetic standpoint but also from the standpoint of prevention of disease. . One of the common conditions in which poor posture may tend to exist is arthritis, particularly that of the rheumatoid type. Peripheral joints are involved and various contractures may cause disturbance of proper posture. This is particularly true if there is flexion of the knee and hip. Even minor flexion deformity of the knees will throw the center of gravity backward, which makes it necessary for the spinal column and trunk to compensate by assuming a forward position. Active involvement of the feet may require the individual to walk with ankles and feet held rigid. This necessitate~ short steps, flexion of the hips and forward flexion of the trunk in order to maintain careful balance. The deformity of the spinal column in the osteo-arthritic, or senile, type of arthritis, or in the Marie-Striimpell type of spondylitis, causes considerable disturbance of postural lines. Infectious spondylitis causes weakness, spasm of muscles, forward slumping of the upper part of the back and flattening of the lower part of the back;· this makes the stooped position. necessary. throwing the center of gravity backwards and making necessary the forward slump. This forward slump may produce many conditions, such as loss of respiratory capacity, increased

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flexion defonnity of the hip and stresses and strains in other parts of the body. Therefore, infectious spondylitis requires particularly constant vigilance on the part of the physician in order to maintain proper erect position of the patient. If erectness cannot be maintained by the musculature, it should be maintained by means of braces. In the presence of inflammatory and traumatic conditions of the peripheral joints, it becomes extremely important to keep them, particularly those of the lower extremities, in a position which is more or less nonnal for locomotion. Otherwise deformities and contractures may cause more disability than the actual disease. Following a surgical operation, the primary factor in producing later malposture may be the concurrent debility. Weakness may produce certain stresses and strains which, in turn, may result in malposture occurring long after the surgical procedure. Following abdominal operations, the patient may tend at first to walk in a stooped position. Loss of muscular power of the erector spine muscles may allow the trunk to slump, thereby changing the weight bearing lines. Proper alignment may not be entirely recovered. Allowing debilitated patients to walk before they have regained the strength of the lower legs and feet may add to foot disabilities later on. The loss of muscular power and the beginning of upright motion may add to strains, stretching of muscles and fatigue which later may produce postural defonnities; these defonnities may remain more or less permanent. Postural deformities should be detected more often than in fact they are detected at present, and exercises should be employed early in order to strengthen muscles, weakness of which might result in malposture. The use of postpartum postural exercises should command attention. After pregnancy, the abdominal muscles may be relaxed and stretched and, if the patient is in the habit of wearing high heeled shoes, the line and center of gravity will be displaced further. If procedures are not used to promote return to nonnal of these muscles, increased lordosis, low .back strain, foot disability and the like may result. More study than has been given should be devoted to the lines of gravity, to the center of gravity in the weight line and to the possible stresses and strains in connection with the various types of paralysis. Paralysis of the abdominal wall in cases

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of poliomyelitis and paralysis of the muscles of the hips and legs produce various abnormal gaits and stance. These abnormalities can be treated by support or re-education or both, thus placing the trunk in a more nearly normal position. In the spastic types of paralysis, muscles should be re-educated and stretched to relieve certain contractures which may throw the patient into malposition in regard to postural lines. The patient should be kept under constant surveillance. Lateral curvature of the spinal column or malalignment in the frontal plane may be due to muscular imbalance, to occupational positions and the like, or to destruction of the bony contour of the skeleton. It is fairly well known that in most cases scoliosis occurs in adolescence. If functional lateral curvature is allowed to persist, the result may be discomfort and disability later in life. In the past the physician has tended to disregard the so-called functional C curvature of the spinal column. However, it has been fairly well established that there is a transitional curvature between the functional and the double, or structural, curvature. In some cases, functional curvature of children apparently can develop into structural curvature. A large percentage of young people have postural deformities and exhibit total curvature. Therefore increased attention should be given by the .physician to ascertaining the ultimate results of these functional C curvatures. It has been fairly well shown that such curvatures can be corrected to a large extent, or at least can be arrested, by proper exercise. In order to give proper exercise in such instances, the cases should be analyzed to determine whether the curvature is due to muscular or skeletal imbalance. COMMENT

It is hoped that the foregoing has made it evident that increased attention should be paid to mechanical and biological elements which enter into malposture. More than casual inspection is required to determine what factors are at work in a case of malposture and what ultimate dysfunction could result. Furthermore, study of malposture cannot be left entirely to the physical educationist or to the physical therapy technician. Far too often the physician orders "active and passive" exercise, or "re-education exercise" without sufficient knowledge of the factors involved to enable him to give specific instructions. Likewise, far too often the physician does not analyze

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dysfunction sufficiently to enable him to determine what rehabilitation can be effected. Malposture should be studied by the physician in order that he, with his knowledge of physiology and pathology, may be able to evaluate conditions and their implications. Knowledge gained from such study of basic principles underlies effective use of therapeutic exercise. REFERENCES

1. Adrian, E. D. and Bronk, D. W.: The Discharge of Impulses in Motor Nerve Fibres. 11. The Frequency of Discharge in Reflex and Voluntary Contraction. J. Physiol., 67:119-151 (Mar. 20) 1929. 2. Baeyer, H. V.: Die Synhapsis in der allgemeinen Gliedermechanik. Report of the 2nd International Orthopedic Congress, London, 1933. 3. Bancroft, Jessie H.: The Posture of School Ch,ildren; with Its Home Hygiene and New Efficiency Methods for Home Training. New York, The Macmillan Company, 1913, 327 pp. 4. Best, C. H. and Taylor, N. B.: The Physiological Basis of Medical Practice, 2nd ed. Baltimore, The WiIliams & Wilkins Company, 1939, pp. 1323-1324. 5. Braune, C. W. and Fischer, Otto: Ueber die Schwerpunktes des menschlichen Korpers mit Riicksicht auf die Ausriistung des deutschen Infanteristen. Abhandl. d. math.-phys. Cl. d. k. siichs. Gesellsch. d. Wissensch. vol. 15, no. 7, 1889. 6. Brunnstrom, Signe: The Changing Conception of Posture. Physiotherapy Rev., 20:79-84 (Mar.-Apr.) 1940. 7. Brunnstrom, Signe: Some Observations of Muscle Function; with Special Reference to Pluriarticular Muscles. Physiotherapy Rev., 22:67-75 (Mar.-Apr.) 1942. 8. Denniston, Helen D.: Value of Exercise in Control of Posture. Arch. Phys. Therapy, 20:220--223 (Apr.) 1939. 9. Drew, Lillian C.: Individual Gymnastics; a Handbook of Corrective and Remedial Gymnastics. Philadelphia, Lea & Febiger, 1923, 260 pp. 10. Elftman, Herbert: The Action of Muscles in the Body. In Biological Symposia: Lancaster, Pennsylvania, The Jaques Cattell Press, 1941, vol. 3, pp. 191-209. 11. Ewerhardt, F. H.: Corrective Exercise. In Barr, D. P.: Modem Medical Therapy in General Practice. Baltimore, The Williams & Wilkins Company, 1940, vol. I, pp. 636-656. 12. Goldthwait, J. E., Brown, L. T., Swaim, L. T. and Kubns, J. G.: Body . Mechanics in Health and Disease; with a Chapter on the Heart and Circulation as Related to Body Mechanics by WiIliam J. Kerr, 3rd ed. Philadelphia, J. B. Lippincott Company, 1941, 361 pp. 13. Gould, A. G. and Dye, J. A.: Exercise and Its Physiology. New York, A. S. Barnes & Company, 1932, pp. 23, 25, 73, and 76-77. 14. Grodins, F. S., Osbome, S. L. and Ivy, A. C.: Present Status of Electrical Stimulation of Denervated Muscle. Arch. Phys. Therapy, 23: 729-733 (Dec.) 1942. 15. Harless, Emil: Beschreibung der Apparate, welche in seiner Abhandlung iiber "die statischen Momente der menschlichen Gliedermassen" zur Auffindung der Lage des allgemeinen Schwerpunktes bezeichnet sind. Miinchen Abhandl., 8:69-96, 1860.

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16. Hill, A. V. and Hartree, W.: The Four Phases of Heat-Production of Muscle Contraction. J. Physiol., H:84-128, 192(}-1921. 17. Jacobson, Edmund: Progressive Relaxation. Chicago, University of Chicago Press, 1929, 429 pp.

18. Kraus, Hans: Behandlung akuter Muskelharten. Wien. klin. Wchnschr., 50:1356-1357 (Oct. 1) 1937. 19. Osgood, R. B.: An Important Etiologic Factor in So-called "Foot Strain." New England J. Med., 226:552-557 (Apr. 2) 1942. 20. Rathbone, Josephine L.: Corrective Physical Education. Philadelphia, W. B. Saunders Company, 1934, 292 pp. 21. Reynolds, Edward and Lovett, R. W.: A Method of Determining the Position of the Centre of Gravity in Its Relation to Certain Bony Landmarks in the Erect Position. Am. J. Physiol., 24:286-293 (May)

1909. 22. Steindler, Arthur: Mechanics of Normal and Pathological Locomotion in Man. Springfield, Illinois, Charles C. Thomas, 1935, pp. 32, 65-<>6, 74, 77, 100 and 196. 23. Todd, Mabe! E.: Principles of Posture. Boston M. & S. J., 182:645-<>49 (June 24) 1920. 24. Todd, Mabel E.: Principles of Posture with Special Reference to the Mechanics of the Hip Joint. Boston M. & S. J., 184:667-<>72 (June 23)

1921.

25. Todd, Mabel E.: The Thinking Body; a Study of the Balancing Forces of Dynamic Man. New York, Paul B. Hoeber, Inc., 1937, 314 pp. 26. Troedsson, B. S.: Some Useful Therapeutic Exercises. M. Rec., 149:307309 (May 3) 1939. ' 27. Wilkins, E. H.: Feet, with Particular Reference to School Children. M. Officer, 66:13-15 (July 12); 21-22 (July 19); 29-30 (July 26); 37-38 (Aug. 2) 1941.