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History of Biomechanics and Kinesiology

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The history of this science goes back to its' definitional beginning. Kinesiology is a combination of the Greek for 'to move' (kinein) and 'logos' (discourse). Kinesiologists - those who discourse on movement-in effect combine anatomy, the science of structure of the body, with physiology, the science of function of the body, to produce kinesiology, the science of movement of the body.

It is usually accepted that Aristotle (384-322 B.C.) is the' ''Father of Kinesiolgy". His treatises, PARTS OF ANIMALS, MOVEMENT OF ANIMALS, and PROGRESSION OF ANIMALS, described the actions of the muscles and subjected them to geometric analysis for the first time. He first to analyzed and described walking, in which rotatory motion is transformed into translatory motion. Further he discussed of the problems of pushing a boat under various conditions was, in essence, a precursor of Newton's three laws of motion. For more information on Aristotle go to Aristotle.

Archimedes (287-212 B.C.), another Greek, determined hydrostatic principles governing floating bodies that are still accepted as swimming. In addition, Heath (1972) suggests that his inquiries included the laws of leverage and determining the center of gravity and the foundation of the oretical mechanics.

Galen (131-201 A.D.) a Roman citizen who tended the Pergamum's gladiators in Asia Minor and is considered to have been the first team physician in history. He used number to describe muscles. His essay DE MOTU MUSCULORUM distinguished between motor and sensory nerves, agonist and antagonist muscles, described tonus, and introduced terms such as diarthrosis and synarthrosis. He taught that muscular contraction resulted from the passage of "animal spirits" from the brain through the nerves to the muscles. Snook (1978) suggested that some writers consider his treatise the first textbook on kinesiology, and he has been termed "the father of sports medicine."

Kinesiology and anatomy lay untouched from the mystical studies of Galen until the 15th century when Leonardo da Vinci (1452-1519) advanced them another step. This artist, engineer, and scientist, da Vinci was particularly interested in the structure of the human body as it relates to performance, center of gravity and the balance and center of resistance. He used letter to identify muscles and nerves in the human body that he retrived from grave yards in the middle ofthe night. ( ) He described the mechanics of the body during standing, walking up and downhill, rising from a sitting position, jumping, and human gait. To demonstrate the progressive action and interaction ofvarious muscles during movement, he suggested that cords be attached to a skeleton at the points oforigin and insertion ofthe muscles. For more information go to Leonardo da Vinci

Galileo, the father of parabolic mathematics, also proved that the flight (trajectory) of a projectile through a non-resitant medium a is a parabola. His work gave impetus to the study of mechanical events in mathematical terms, which in turn provided a basis for the emergence of kinesiology as a science.

The Italian Jesuit Francesco Maria Grimaldi was the first to report hearing sounds made by contracting muscles. Although his book, Physicomatheis de Itlmine, was published in 1663, 2 years after his death, techniques for studying these sounds were not available until 300 years later. In the last few years, the invention of the electronic stethoscope and computer analyses have made research in this field feasible. Oster has shown that the amplitude ofmuscle sound is directly proportionate to the weight used to maintain a constant contraction. These sounds appear to originate from the vibration of single muscle fibers, particularly the fast-twitch fibers. In the future it may be possible to use such sounds to determine which muscles are active in a given movement and how hard each is working.(Oster, 1984).

The circulation of the blood through the. body was first demonstrated by William Harvey (1578-1657), although he erroneously attributed to the heart the fundion of recharging the blood with heat and "vital spirit." (Harvey, 1959). Subsequently, Niels Stensen (1648-1686) made the then-sensational declaration that the heart was merely a muscle, not the seat of "natural warmth," nor of "vital spirit." This has been acclaimed as the greatest advance in our knowledge ofthe circulatory system since Harvey's discovery (Miller, 1914). Three years later, Stensen, who has been credited with laying the foundation of muscular mechanics, wrote Elrmentorum Myologiae Spccimm, an "epoch-making" book on muscular function. In this book he asserted that a muscle is essentially a collection of motor fibers; that in composition the center of a muscle differs from the ends (tendons) and is the only part that contracts. Contraction of a muscle, wrote Stensen, is merely the shortening of its individual fibers and is not produced by an inrrease orlossofsubstance. (Rzlton, 1926).

The word "orthopedics" was coined by Nicolas Andry (1658-1742) from the Greek roots "orthos," meaning "straight," and "pais," meaning "child." Andry believed that skeletal deformities result from muscular imbalances during childhood. In his treatise, ORTHOPEDICS or the ART OF PREVENTING AND CORRECTING IN INFANTS DEFORMITIES OF THE BODY, originally published in 1741, he defined the term "orthopedist" as a physician who prescribes corrective exercise. (Andy, 1961). Although this is not the modern usage, Andy is recognized as the creator ofboth the word and the science. His theories were directly antecedent to the development of the Swedish system of gymnastics by Per Henrik Ling (1776-1839).

In PRINCIPIA MATHEMATICA PHILOSOPHIAE NATURALIS, which is "perhaps the most powerful and original piece of scientific reasoning ever published," (Taylor, 1949). Isaac Newton (1642-1727) laid the foundation ofmodern dynamics. Particularly important to the future of kinesiology was his formulation of the three laws of rest and movement, which express the relationships between forces (interaction) and their effects:

I. Every body continues in its state of rest, or of uniform motion, in a right line, unless it is compelled to change that state by forces impressed upon it. (This is sometimes known as the law of inertia and was originally proposed by Galileo in 1638.)

II. The change of motion is proportional to the motive force impressed and made in the direction ofthe right line in which that force is impressed (law of momentum).

III. To every action there is always opposed an equal reaction; or, the mutual actions of two bodies upon each other are always equal and directed to the contrary parts (law of interaction). (Newton, 1668).

The application of these laws to muscular function may be demonstrated by the following analogy: While he is pivoting, a discus thrower must grasp the discus firmly (exert centripetal force) to prevent it from flying out of his hand. In accordance with the third law, the missile exerts an equal and opposite reaction (centrifugal force). When his grip is released and centripetal force no longer interacts with the discus, the implement flies off in a straight line tangential to its former circular path. The distance covered by the missile is proportionate to the motive force imparted to it, in accordance with the second law. The trajectory of the missile is affected by gravity, wind velocity, and other forces tending to alter its state of uniform motion, as predicted by the first law.

According to the Newtonian world view, changes of motion are considered as a measure of the force that produces them. From this theory originated the idea of measuring force by the product of mass and 0degreesacceleration, a concept that plays a fundamental role in kinetics. The greater the speed with which the discus thrower whirls, the greater the acceleration applied to the mass of the discus, the farther it will fly before gravity returns it to, earth, and the greater the force said to have been applied to the discus.

Newton is also credited with the first correct general statement of the parallelogram offorce, based on his observation that a moving body affected by two independent forces acting simultaneously moved along a diagonal equal to the vector sum of the forces acting independently. By further analysis of the laws ofmovement as applied by the discus thrower, it can be demonstrated mathematically that the horizontal and vertical forces acting on the flying discus are equal. The diagonal, which is equal to the vector sum ofthe horizontal and vertical forces, is, therefore, 45 degrees , and the missile should traverse the greatest distance when it travels at this angle. In practice, of course, other fadors oflift, drag, shape, gyroscopic rotation, and so forth enter the situation, and it is possible that the : most effective angle of release may not always be the one that is the theoretical optimum. Because two or more muscles may pull on a common point ofinsertion, each at a different angle and with a different force, the resolution of vectors of this type is a matter of considerable importance in the solution of academic problems in kinesiology.

Within the recent past, physicists have demonstrated that Newton's theories are valid only within the frame ofreference in which they were conceived; they do not apply to relationships between forces in the Einsteinian world view. This discovery has little significance for the kinesiologist, however, since he deals primarily with the forces of gross muscular movement, and these are governed by the laws of motion set forth by Newton.

In his studies of muscular contraction, James Keill (1674-1719) calculated the number of fibers in certain muscles, assumed that on contraction each fiber became spherical and thus shortened, and from this deduced the amount of tension developed by each fiber to lift a givenweight. In AN ACCOUNT OF ANIMAL SECRETION, THE AMOUNT OF BLOOD IN THE HURMAN BODY, AND MUSCULAR MOTION (1708), Keill drew the erroneous conclusion that a muscle could not contract to less than two thirds ofits great

In AN ESSAY ON THE VITAL AND OTHER INVOLUNTARY MOTIONS OF ANIMALS, published in 1751, Robert Whytt (1714-1766) rejected Baglivi's theory of muscular action and contended that movement originates from an unconscious sentient principle, or soul. This idea brought him into disagreement with von Haller (French, 1969). Possibly Whytt may not have comprehended the principle that movement may originate as reflex reaction to external stimuli; however, it appears that he was cognizant of the stretch reflex and the fact that a given stimulus may be adequate to excite one nerve ending but not another. Their differences of opinion arose from the fact that von Haller thought in terms of isolated muscle, and Whytt in terms of the reflex control of the movements of an organism.

The subject of anatomy, as taught prior to the time of Marie Francois Xavier Bichat (1771-1802), consisted of little more than dogmatic statements handed down through the ages. Through Bichat's efforts, anatomy became a science solidly founded on the systematic experimentation with the various systems into which he divided the living organism. Bichat observed that the organs of the body are composed ofindividual tissues with distinctive characteristics and was the first to describe the synovialmembranes. Bichat is regarded as the author of the modern concept of structure as the basis of function, which led to the development of rational physiology and pathology.

He distinguished between the cerebrospinal nervous system, which deals with the external relationships between the animal and its environment, and the autonomic nervous system, which controls the organs ofinternal function. The six Croonian Lectures on Muscle Motion

[william Croone (1633-1684), a professor at Gresham College, England, and author of De Ratione Motus Mrrs culorum (1664), an important early work on muscle, left a will providing for annual lectures on the physiology of muscular motion. Fulton commented, "It is literally true that the history of muscle physiology in the Eighteenth, Nineteenth and Twentieth Centuries has been largely developed at these annual lectures." (Muscular Contraction and the Reflex Control of Movement, pp. 15-16.) ]

* delivered by John Hunter (1728-1793) in 1776, 1777, 1779, 1780, 1781, and 1782,": brought together all of this great anatomist's observations concerning the structure and power of muscles and the stimuli by which they are excited. Muscle, he declared, while endowed with life, is fitted for self-motion, and is the only part ofthe body so fitted. He emphasized that muscular function could be studied only by observations of living persons, not cadavers. In his lecture series, Hunter described muscular function in considerable detail, including the origin, insertion, and shape ofmuscles, the mechanical arrangement of their fibers, the two-joint problem, contraction and relaxation, strength, hypertrophy, and many other aspects ofthe subject. His lectures may be regarded as summarizing all that was known about kinesiology at the end ofthe eighteenth century, when, unwittingly, kinesiologists stood at the threshold of a discovery that was to revolutionize their methods of investigation.

About 1740 physiologists became excited over the phenomena produced by electrical stimulation ofmuscles. Haller summarized many ofthe early experiments in his treatise on muscle initability, and Whytt reported clinical observations on a patient treated by electrotherapy. "Animal electricity" was proposed as a substitute for the "animal spirits" that earlier investigators had believed to be the activating force in muscular movement. During the summer of 1786, Luigi Galvani (1737 - 1798) studied the effects of atmospheric electricity on dissected frog muscles. He observed that the muscles of a frog sometimes contracted when touched by a scalpel, which led him to the conclusion that there was "in dwelling electricity which proceeded along the nerve." His Commentary on thr Effects of Electricity on Muscular n/lotion (1791) is probably the earliest explicit statement of the presence of electrical potentials in nerve and muscle. Galvani is considered the father of experimental neurology.

The study of animal electricity at once became the absorbing interest of the physiologic world. The greatest name among the early students ofthe subject was Emil DuBois-Reymond (1818-1896), who laid the foundations of modern electrophysiology.

Fascinated by the prospect of investigating muscular response produced by electrical stimulation, Guillaume Benjamin Amand Duchenne (1806 - 1875) set out to classify the functions of individual muscles in relation to body movements, although he recognized that isolated muscular action does not exist in nature (Duchenne, 1959). His masterwork, PHYSIOLOGIE DES MOUVEMENTS, appeared in 1865 and has been acclaimed "one ofthe greatest books of all times."(Jokl, 1956).

The modern concept oflocomotion originated with the studies ofBorelli; however, very little was accomplished in this field prior to the publication of DIE MECHANIK DER MENSCHLICHEN GERVERKZEUGE by the Webers in 1836. Their treatise, which still stands as the classical work accomplished by purely observational methods, firmly established the mechanism of muscular action on a scientific basis. The Weber brothers, Emst Heinrich (1795-1878), Wilhelm Eduard (1804-1891), and Eduard Friedrick Wilhelm (1806-1871), believed that the body was maintained in the erect position primarily by tension of the ligaments, with little or no muscular exertion; that in walking or running the forward motion ofthe limb is a pendulum-swing owing to gravity; and that walking is a movement offalling forward, arrested by the weight ofthe body thrown on the limb as it is advanced forward. The Webers were the first to investigate the reduction in the length of an individual muscle during contraction and devoted much study to the role of bones as mechanical levers. They were also the first to describe in chronologic detail the movements of the center of gravity.

The study of animal mechanics was expanded by the talented and versatile Samuel Haughton (1821-1897) in numerous papers bearing such titles as OUTLINES OF A NEW THEORY OF MUSCULLAR ACTION (1863), THE MUSCULNV MECHANISM OF THE LEG OF THE OSTRIH (1865), ON HANGING, CONSIDERED FROM A MRECHANICAL AND PHYSIOLOGICAL POINT OF VEIW, (1868), AND NOTES ON ANIMAL MECHANICS (1861-1865). However, advancement of knowledge concerning body mechanics was greatly impeded by lack of a satisfactory method of chronologic reproduction of movement. This advance was made when Janssen, an astronomer who had used serial pictures in 1878 to study the transit of Venus, suggested kinematographic pictures to study human motion. Eadweard Muybridge : (1831-1904) produced his book THE HORSE IN MOTION in 1882, and in 1887 wrote his monumental Animal Locomotion in eleven volumes, an abridgment of which was reissued in 1955 under the title The Human Figure in Motio. (Muybridge, 1955). Etienne Jules Marey(1830-1904), who was convinced that movement is the most important of human functions and that all other functions are concerned with its accomplishment, described graphic and photographic methods for biological research in DU MOUVEMENT DANS LES FUNLCTIORLS DA LA VIE (1892) and LE MOUVENENT (1894).

These photographic techniques opened the way for the experimental studies of Christian Wilhelm Braune (1831-1892) and Otto Fischer (1861 - 1917), which are still considered of major importance in the study of human gait. Even more famous than these investigations was Braune and Fischer's report of an experimental method of determining the center of gravity, published in 1889. An abridgment ofthis is available in an Air Force Technical Documentary Report (Aerospace, 1963). Their major premise was that a knowledge of the position of fhe center of gravity of the human body and of the body's component parts was fundamental to an understanding of the resistive forces that the muscles must overcome during movement. Their observations were made on four cadavers, which, after having been preserved by freezing, were nailed to a wall by means oflong steel spits. The planes ofthe centers of gravity of the longitudinal, sagittal, and frontal axes were thus determined. By dissecting the bodies with a saw and locating the points of intersection of the three planes, Braune and Fischer were able to establish the center of gravity of the body. The center of gravity of the component parts was determined in the same manner. Because one cadaver began to decompose and the investigators were not permitted to dissect a second cadaver, complete observations were made on only two of the four bodies. When the centers of gravity were plotted on a life-size drawing of one of the cadavers and compared photographically with those of a soldier having similar body measurements, the investigators observed a remarkable similarity. Braune and Fischer concluded that the original position of their frozen cadavers could be considered a normal one and referred to it as "normalstellung," which was intended to indicate only that it was the standard position in which their measurements were taken. Unfortunately, this term came to be understood as the ideal position, and generations of students were exhorted to imitate it. Their work with cadavers has recently been carried on and extended by Wilfrid Taylor Dempster. (Dempster, 1955).

On the basis of subsequent studies, Rudolf A. Fick (1886-1939) concluded that the theory of "normalstellung" was not entirely valid, as the recumbent position of a cadaver could not be transferred to the vertical stance. The degree of lumbar lordosis is much less when the body is recumbent than when vertical; in the latter position the center of gravity shifts forward considerably more than Braune and Fischer assumed. Fick contended that no one posture is common for people of all races and cultures. Modern anthropological investigations have confirmed his opinion.

The late nineteenth and early twentieth centuries were most productive of physiologic studies closely related to kinesiology. Adolf Eugen Fick (1829 - 1901) made important contributions to our knowledge of the mechanics of muscular movement and energetics and introduced the terms "isometric" and "isotonic." The study of developmental mechanics was introduced by Wilhelm Roux (1850 - 1924), who stated that muscular hypertrophy develops only after a muscle is forced to work intensively, a point ofview that was later demonstrated experimentally by Werner W. Siebert." (Siedber, 1960). B. Morpurgo showed that increased strength and hypertrophy are a result of an increase in the diameter of the individual fibers of a muscle, not a result of an increase in the number of libers. The theory of progressive resistance exercise is based principally on the studies of Morpurgo and Siebert (Steinhaus, 1955) but Morpurgo's work is now being questioned.

L. Ranvier, about 1880, discovered the difference in the speeds of contraction of red and white muscle. "The importance ofhis finding," says Granit, "is that it brought functional aspects into the focus of subsequent research." (Granit, 1970).

Ranvier

The trajectorial theory was supported by Roux and became the basis for his interpretation of the trajectory system of other bones. In 1892 this theory was classically expressed by Tulius Wolff ( 1836- 1902) in the famous Wolff s law: "Every change in the form and function of a bone or of their function alone is followed by certain definite changes in their internal architecture, and equally definite secondary alteration in their external conformation, in accordance with mathematical laws." He believed that the formation of bone results from both the force of muscular tensions and the resultant static stresses of maintaining the body in the erect position, and that these forces always intersect at right angles. Wolff s law also applies to the healing of skin wounds.

Bassett has proposed a restatement of Wolffs law in modern terms: "The form of the bone being given, the bone elements place or displace themselves in the direction of the functional pressures and increase or decrease their mass to reflect the amount of functional pressure." (Basset, 1968). The probable mechanism is biochemical-a-piezoelectric effect ofthe bone crystal or from a diode with collagen and mineral components. In his paper "Laws of Bone Architecture," which has been proclaimed "the most thorough study of stress and strain in a bone by mathematical analysis of cross sections. John C. Koch concluded that the compact and spongy materials of bone are so composed as to produce maximum strength with a minimum of material and that, in form and structure, bones are designed to resist in the most economical manner the maximum compressive stresses normally produced by the body weight. Because the stresses from body weight are so much greater than the tensions that are normally produced by the muscles, reasoned Koch, the effect ofmuscular action is of relatively little importance in determining the architecture ofthe bones and, therefore, could be ignored in his analysis. In endeavoring to draw practical applications from his theoretical studies, Koch commented that alterations in posture increase the stress in certain regions and decrease it in others, and that ifpostural alterations are maintained, the inner structure of the affected bones is altered. The proper mechanical means of counteracting these alterations, said Koch, was to impose new mechanical conditions by the use of braces, jackets, or other suitable devices to reverse the transformative process and restore the original structure.

Murk Jansen's monograph ON BONE FORMATION (1920) disagreed with many of Wolffs premises, including the "dualistic" doctrine that bone formation is dependent on both tension and pressure. Wolffs hypothesis that these forces intersect at right-angles in the trabeculae of cancellous bone constituted a fatal flaw in the theory, contended Jansen, since the major frabecular systems do not always cross at right angles. Jansen insisted that the jerking action of a contracting muscle, combined with gravity, is the chief mechanical stimulus for the formation ofbone and, moreover, is a deten„ainative factor in the structure of cancellous bone.

Eben J. Carey (1929) also criticized Koch's denial ofthe role ofmuscular tension in the formation ofbone and asserted that the dominant factors affecting the growth and structure ofbone are the powerful back pressure vectors produced by the forces of muscular contraction. He rejected Koch's emphasis on static pressure. The body, he said, is sustained in the upright posture by mutual interaction between the skeleton and the muscles, and he expressed the opinion that the dynamic action of the muscles may exceed the static pressure ofbody weight. He contended that the normal growth and structure of mature bone is the result of this dynamic muscular activity and of the intrinsic capacity of skeletal cells to proliferate centrifugally against extrinsic centripetal resistances.

F. Pauwels endeavored to demonstrate that muscles and ligaments act as traction braces to reduce the magnitude of stress in the bones. His work was criticized by F. Gaynor Evans on the grounds that it was concerned only with the stresses produced by loads placed on solid models shaped like bones. It is possible that Wolff and Roux overemphasized the importance of mechanical stresses without proper consideration for biological factors, which sometimes exceed mechanical influences. Nevertheless, the theory of functional adaptation to static stress remains a major hypothesis in the study of skeletal development. J. H. Scott (1957) has reviewed the material in the field in an effort to construct a working hypothesis of the developmental and functional relationships between the skeletal system and the neuromuscular system.

Prior even to the time when the development ofbone became a subject ofheated debate, even more highly controversial hypotheses were introduced into the scientific world. Charles Darwin (1809-1882) published two books. THE ORIGIN OF THE SPECIES (1859) and THE DESCELZT OF MAN (1871), which have become classics and have revolutionized man's ideas concerning the human body. Darwin's conception ofman as a "modified descendant of some pre-existing form" whose framework is constructed on the same model as that of other mammals, and whose body contains both rudimentary muscles that serve useful functions in the lower mammals and modified structures that resulted from a gradual change from quadrupedal to bipedal posture, was at first bitterly opposed. Now generally accepted, his concepts have clarified many questions pertaining to kinesiology that might otherwise have remained obscure and have attracted to the study of kinesiology many physical anthropologists whose contrabutions have been of great value.

Yet another scientist of the nineteer century, Angelo Mosso (1848 - 1910), made an important contribution to the study of kinesiology, the invention ofthe ergograph in 1884. This instrument, now available in an endless array of specialized forms, has become a nearly indispensable tool for the study of muscular function in the human body.

The first extensive compendium on body mechanics, THE HUMAN MOTOR, by Jules Amar, was published in 1914. Inspired largely by the increase in work productivity achieved by Frederick Winslow Taylor's (1972) application of scientific principles of body mechanics to industry, Amar (1879 - ?) sought to bring together "in one volume all the physical and physiological elements ofindustrial workÓ (Amar, 1972). Since its publication, countless industrial studies based on Amar's principles have been published, perhaps the best known ofwhich are the numerous reports ofthe British industrial Fatigue Research Board and of Frank B. (1868-1924) and Lillian M. (1878-1972) Gilbreth.

This type of kinesiologic research initiated studies in the unexplored areas of time and motion. Investigationsin this field have been greatly accelerated as a result ofrapid advances in engineering and the development of machines so complex that the physical abilities of the human operator become a limiting factor in their use. Scientists have brought together massive collections of data pertaining to the application of scientific principles ofbody mechanics to industry, now known as human engineering, or the science of ergonomics--"the customs, habits, or laws of work." Attempts to solve the problem of space flight have provided further impetus studies of this nature.

Kinesiology of the HUMAN BODY UNDER NORMAL AND PATHOLOGYICAL CONDITIONS, by Arthur Steindler (1878-1959), was an important contrabution to our understanding of body mechanics. Information has continued to accumulate, and some of the facts and theories that have been presented are both curious and instructive. As an example, men frequently sustain femoral fractures as a result of automobile accidents, whereas women are more likely to incur dislocations ofthe hip. This difference is attributed to the social conditioning ofwomen to sit with their knees or legs crossed, whereas men are conditioned sit with their legs spread apart. An impact on a person sitting with the knees or legs crssed tends to drive the head of the femur into the acetabulum, but a similar impact Idy ofindividual sitting with his legs apartter drive the head ofthe femur further in 1 body acetabulum until the femur buckle!

As early as 1880, Wedenski demonsted by the existence of action currents in human muscles, although practical use of this disovery had to await the invention of a more sensitive instrument. This became available when W Einthoven developed the string galivanometer in 1906. The physiologic aspects of electromyography were first discussed in a paper by H. Piper, of Germany, 1910-1912; however, interest in the subject did not become widespread in the English-speaking countries until publication of a report E. D. Adrian in 1925. (Adrian, 1925). By utilizing electromyographic techniques, Adrian demonstrated for the first time that it was possible to determine the amount of activity in the been human muscles at any stage of a movement. The development of the electromyograph represents one of the greatest advances kinesiology. By means of this instrument many generally accepted concepts of muscle action have been proved erroneous and new theories have been brought forth. In this area the work ofJohn V. Basmajian has been of particular value to students ofkinesiology and is frequently cited in this book. (Basmajian, 1977).

The brilliant studies of Archibald V. Hill ( 1886- 1977) in the oxygen consumption ofmuscle won him a share in a Nobel Prize om 1922. Hugh E. Huxley's (1924- ) work in the ultrastructure of striated muscle and Andrew F. Huxley's (1917- ) studies in the physiology of striated muscle distinguish them as leading authorities in their respective fields. (Hill, 1971; Huxley, H. E., 1971; Huxley, A. F., 1971).

Interest in the subject of posture has declined among kinesiologists in the United States during the last few years. In part, result decline may have resulted from general acceptance of the dictum that "the physiological benefits obtained from correction of common postural defects are mostly imaginary" (Karpovich, 1965) in part, it may reflect fhe growing realization that individual differences almost preclude valid generalizations. Perhaps much ofthe effort that in earlier times was dfvoted to the study of static posture is now direded to research concerning dynamic locomotion. Wallace Fenn (1893-1971), Plato Schwartz, Verne Inmann, Herbert Elftman, Dudley Morton, and Steindler should be listed among the scientists who have made important con-ibutions to knowledge concerninR this phase of kinesiology.

The use of cinematography for kinesiological studies of athletes and industrial workers has become commonplace. An important recent development in the study of human motion is the use of cineradiographic techniques.

Muybridge.

In time, advances in techniqut may make it possible to record the complete sequence of musculoskeletal movements rather than onlv a fraction of them. A fascinating new parameter was opened up with the invention of the electronic stroboscope by Harold Edgerton. This instrument, which is capable of exposures as short as one millionth ol a second, can record in a series of instantaneous photographs an entire sequence of movement. This apparatus seems particularly promising for analysis of the various sequences of skilled movement. In a somewhat related field, the science of aerodynamics has greatly increased our knowledge of the movement of objects in space through investigations involving the use of wind tunnels and other specialized research tools and artificially produced environments.

Psychologists, psychoanalysts, psychiatrists, and other social scientists have become interested in investigating the psychosomatic aspects of kinesiology. The studies of J. H. Van Den BerR, Edwin Straus, and Temple Fay may be cited as representative analyses that have contributed significantly to our knowledge concerning the "why" of human movement." (Van Den Berg, 1952; Straus, 1953; Fay, 1955).

According to the old psychologic stimulus-response theory, the individual is merely a communication channel between the input and fhe output. This view fails to consider the contribution that the individual makes to the circuit. In information theory it is recognized that through experience man accumulates certain knowledge about his external environment, such as how an object travels through space, and that the signals he receives from his kinesthetic proprioceptors reveal to him how his body is responding to the external presentation. The individual is viewed as a limited-capacity channel, receiving and responding to signals originating from internal sources as well as from the external display. The relative importance ofthese two types of stimuli in determining individual response appears to vary with pradice and with the ease or difficulty of the required responst. One of the chief dimculties confronting a performer is to separate one signal from another when they are presented in rapid succession. rerception of essential data is usually obscured by compefng signals that create "noise" on the input circuits. A distinguishing characteristic of a skilled performer is his ability to select, infegrate, and respond only to those signals that are germane to the situation; that is, in effect, to filter out signals that are mere noise. The fact that stimuli mav be correlated with each other mav enhance Ihe difficulty for the performer.

Engineering theory treats communications systems as organisms. Because the two are operationally equivalent (Table 1-1), the insights of the cyberneticians (scientists who postulate that the processes of control are similar in the animal, the machine, and an organizational structure) and the psychologists are also equivalent and may be used interchangeably.

The modifications that a man makes in his environment cause a change of input from that environment into his organism. Feedback from these functional alterations affect his structure. Alterations of structure affect the relationship between the various components and result in changes in function. Thus man to some extent is his own architect.

Since the appearance of the first edition of this book, the physiologically motivated researchers largely have concerned themselves with the waveforms of electrical activity in the nerves or brain or in the transmission properties of nerve tissue. Psychologically oriented investigators have tended to search for regular descriptions of the input-output of the human organisms. For example, the neurogeometric theory holds that the receptor and the motor systems are linked by space-time organized feedback mechanisms. These are multidimensional. Motion is made up ofposture, transport, manipulation, and tremor movements, each controlled by its own sensory feedback. The brain coordinates and regulates these feedbacks. Learning is thus based on the brain's integration of the anatomic and physiologic relations between the efferent and the afferent systems.

Such new insights have rich import for kinesiology, but also introduce new complications. The advanced student must now become accustomed to such explanations as the suggestion that a smooth landing after a drop is due to the release of a "complete preprogrammed open-loop sequence of neuromuscular activity virtually unaided by myotatic feedback." (Watt, 1966)

While further use of the electromyograph will continue to refine our understanding of how the body functions, it seems unlikely that additional major surprises will emerge from this technique. Probably, the next important advances will result from computer simulation studies, particularly of situations in which it would be impossible to use human subjects.

In the second half of the twentieth century, kinesiology has gradually emerged as a distinct entity in the family of scholarly scientific disciplines. Like all disciplines, its origins have been in discrete human needs and pradical problems; its organized form has become much more comprehensive and theoretically integrated. As a discipline, the focus is on the movement behavior of living organisms.

The Society for Behavioral Kinesiology has defined behavioral kinesiology as "the science of the structures and processes of human movement and their modification by inherent factors, by environmental events, and by therapeutic intervention." Although definitions such as this have done much to expand the concept of kinesiology beyond the historical constraints of "applied anatomy," the limitation of a discipline to the study of human phenomena and applications is inappropriate and has not been characteristic of other biologically based disciplines. For one thing,such limitation excludes the impressive body covered by scientific research these paradigms are found to be unable to explain them. A crisis arises, and new theories are devised to explain these anomalies. In effect, a scientific revolution occurs.

The next generation of scitntists has a new world view and poses quesfions that were not even conceivable under the old theories. Rather than being a linear progression in which each step brings mankind closer to "the truth," scientific development is a process of evolution whose successive stages are characterized by an increasing understanding ofnature. It is, Kuhn (1970) suggests, evolution from what we know to evolution toward wha t we wish to know. Unfortunately space here is insufficient to discuss this further. Students who wish to tlrlderstand how the developments described in this chapter actually occurred will find Kuhn's booklet an essential guide.

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