biomechanics

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biomechanics

the study of the mechanics of the movement of living organisms

Biomechanics

A field that combines the disciplines of biology and engineering mechanics and utilizes the tools of physics, mathematics, and engineering to quantitatively describe the properties of biological materials. One of its basic properties is embodied in so-called constitutive laws, which fundamentally describe the properties of constituents, independent of size or geometry, and specifically how a material deforms in response to applied forces. For most inert materials, measurement of the forces and deformations is straightforward by means of commercially available devices or sensors that can be attached to a test specimen. Many materials, ranging from steel to rubber, have linear constitutive laws, with the proportionality constant (elastic modulus) between the deformation and applied forces providing a simple index to distinguish the soft rubber from the stiff steel. While the same basic principles apply to living tissues, the complex composition of tissues makes obtaining constitutive laws difficult.

Most tissues are too soft for the available sensors, so direct attachment not only will distort what is being measured but also will damage the tissue. Devices are needed that use optical, Doppler ultrasound, electromagnetic, and electrostatic principles to measure deformations and forces without having to touch the tissue.

All living tissues have numerous constituents, each of which may have distinctive mechanical properties. For example, elastin fibers give some tissues (such as blood vessel walls) their spring-like quality at lower loads; inextensible collagen fibers that are initially wavy and unable to bear much load become straightened to bear almost all of the higher loads; and muscle fibers contract and relax to dramatically change their properties from moment to moment. Interconnecting all these fibers are fluids, proteins, and other materials that contribute mechanical properties to the tissue.

The mechanical property of the tissue depends not only upon the inherent properties of its constituents but also upon how the constituents are arranged relative to each other. Thus, different mechanical properties occur in living tissues than in inert materials. For most living tissues, there is a nonlinear relationship between the deformations and the applied forces, obviating a simple index like the elastic modulus to describe the material. In addition, the complex arrangement of the constituents leads to material properties that possess directionality; that is, unlike most inert materials that have the same properties regardless of which direction is examined, living tissues have distinct properties dependent upon the direction examined. Finally, while most inert materials undergo small (a few percent) deformations, many living tissues and cells can deform by several hundred percent. Thus, the mathematics necessary to describe the deformations is much more complicated than with small deformations.

The biomechanical properties and behaviors of organs and organ systems stem from the ensemble characteristics of their component cells and extracellular materials, which vary widely in structure and composition and hence in biomechanical properties. An example of this complexity is provided by the cardiovascular system, which is composed of the heart, blood vessels, and blood. See Cardiovascular system

Blood is a suspension of blood cells in plasma. The mammalian red blood cell consists of a membrane enveloping a homogeneous cytoplasm rich in hemoglobin, but it has no nucleus or organelles. While the plasma and the cytoplasm behave as fluids, the red blood cell membrane has viscoelastic properties; its elastic modulus in uniaxial deformation at a constant area is four orders of magnitude lower than that for areal deformation. This type of biomechanical property, which is unusual in nonbiological materials, is attributable to the molecular structure of the membrane: the lipid membrane has spanning proteins that are linked to the underlying spectrin network. The other blood cells (leukocytes and platelets) and the endothelial cells lining the vessel wall are more complex in composition and biomechanics; they have nuclei, organelles, and a cytoskeletal network of proteins. Furthermore, they have some capacity for active motility. See Blood, Cytoskeleton

Cardiac muscle and vascular smooth muscle cells have organized contractile proteins that can generate active tension in addition to passive elasticity. Muscle cells, like other cells, are surrounded by extracellular matrix, and cell-matrix interaction plays an important role in governing the biomechanical properties and functions of cardiovascular tissues and organs. The study of the overall performance of the cardiovascular system involves measurements of pressure and flow. The pressure-flow relationship results from the interaction of the biomechanical functions of the heart, blood, and vasculature. To analyze the biomechanical behavior of cells, tissues, organs, and systems, a combination of experimental measurements and theoretical modeling is necessary. See Muscle

Other organ systems present many quantitative and qualitative differences in biomechanical properties. For example, because the cardiovascular system is composed of soft tissues whereas bone is a hard tissue, the viscoelastic coefficients and mechanical behaviors are quite different. Cartilage is intermediate in stiffness and requires a poro- elastic theory to explain its behavior in lubrication of joints. In general, living systems differ from most physical systems in their nonhomogeneity, nonlinear behavior, capacity to generate active tension and motion, and ability to undergo adaptive changes and to effect repair. The biomechanical properties of the living systems are closely coupled with biochemical and metabolic activities, and they are controlled and regulated by neural and humoral mechanisms to optimize performance. While the biomechanical behaviors of cells, tissues, and organs are determined by their biochemical and molecular composition, mechanical forces can, in turn, modulate the gene expression and biochemical composition of the living system at the molecular level. Thus, a close coupling exists between biomechanics and biochemistry, and the understanding of biomechanics requires an interdisciplinary approach involving biology, medicine, and engineering.

Biomechanics

 

a branch of biophysics concerned with the mechanical properties of live tissues, organs, and the organism as a whole, as well as the mechanical phenomena occurring therein. Biomechanics was once regarded as a branch of embryology, that is, developmental mechanics, frequently called experimental embryology. The word is usually applied to the study of the movements of man and animals. However, in the middle of the 20th century the scope of research in biomechanics was broadened. The biomechanics of the respiratory apparatus studies its elastic and inelastic resistance, its kinematics (that is, the geometric characteristics of motion), and the dynamics of respiratory movements, as well as investigating other aspects of the functioning of the respiratory apparatus as a whole and of its parts (lungs, chest). The biomechanics of blood circulation studies the elasticity of the blood vessels and heart, hydraulic resistance of the blood vessels to the blood flow, propagation of elastic oscillations along the vascular wall, flow of blood, functioning of the heart, and other aspects of hemodynamics. The biomechanics of movements, based on the data of anatomy and theoretical mechanics, investigates the structure of the locomotor organs, the nature of the application of muscular force that causes movements in the joints, the kinematics of articulations, the distribution of the body mass along its members, and the patterns of movement of these members and of the body as a whole. It also determines the character, direction, and role of the motive forces. The biomechanical characteristics of motion are based on the data of structural, kinematic, and dynamic analysis. Structural analysis determines the number of degrees of freedom of the kinematic circuits of the body and their nature (open, closed). Kinematic analysis describes movements (trajectory, velocity, and acceleration). Dynamic analysis reveals the pattern of the interaction of internal and external forces. The objective of biomechanical research is, most often, to determine the pattern of the motive forces from the kinematic characteristics of motion. This information is useful in assessing the economy of motion and the degree of utilization of both external and muscular forces and in evaluating the mechanisms of coordination and regulation of movements. In this respect biomechanics verges on the physiology of movements. Another objective of biomechanical research is to study the individual body positions (such as standing and sitting). In doing so it determines the significance of static moments, the position of the general center of gravity of the body in relation to support, and the degree of steadiness of the body in a given position; that is, it essentially establishes the nature of the interaction of external and internal forces. The solution to these problems is also bound up with physiology and with studies on the position and balance of the body in space.

Research workers in biomechanics use various techniques for recording changes, velocities, and accelerations of the movements under study. Optical methods are the commonest: high-speed motion picture, photography, cyclography, kymocyclography, and other methods. They help to determine spatial movements of the body and the movements of its members in relation to each other. They are of value in calculating linear and angular velocities, accelerations, and effective forces. Biomechanics also makes use of techniques of electrical recording of mechanical quantities by means of mechanotrons, sensors of angular movements, and support dynamographs.

History of biomechanics. Research in biomechanics was started by Leonardo da Vinci, who studied human movements from the standpoint of anatomy and mechanics. The development of biomechanics was greatly influenced by G. Borelli, who regarded the body as a machine and tried to explain respiration, blood flow, and muscle work from the standpoint of mechanics. In his book Movement of Animals (1680–81), Borelli gave a mechanical analysis of the movements of the members of the body of man and animals when walking, running, and swimming. Human walking was experimentally studied by the German scientists E. and W. Weber (1836) and W. Braune and O. Fischer (1895), the French scientist E. Marey (1894), and the Americans W. O. Fenn (1935) and H. Alftman (1938). The American scientists F. G. Evans (1957) and H. Frost (1964) studied the mechanics of live tissues. The biomechanics of respiration were investigated by the American scientist J. A. Clements (1965) and that of hemodynamics by his countrymen H. L. Taylor (1953) and E. O. Attinger (1964). The development of biomechanics in Russia was promoted by the works on theoretical anatomy of P. F. Lesgaft (1905) and by I. M. Sechenov’s book Outline of the Working Movements of Man (1901) which summarizes the most important biomechanical characteristics of human movements. The study of biomechanics was initially of an applied character and was directed toward the efficient use of work space, work position, shape of tools, and methods of work. Cyclography and cyclogrammetry were the techniques used. Detailed studies on human locomotion were carried out by N. A. Bernshtein and his coworkers. They made a biodynamic analysis of the walking of healthy people, the evolution of walking in children and old persons, and also running, jumping, and marching.

Practical significance. Research in biomechanics is of great value in various fields of knowledge. The physiology of work and sports is one; another is military and clinical medicine, including neurology, orthopedics, traumatology, and prosthetics. For example, study of the biomechanics of physical exercise and sports movements is useful in discovering the basis of skills and in working out a scientific system of training. Study of the work movements of man makes it possible to assess the economy of a particular variation of movements and to perfect its structure. Study of the stability of bones, joints, and ligaments and also the elasticity and tensility of muscles and other tissues is important for traumatology and orthopedics, as well as for understanding the mechanisms of action of injurious factors and for preventing traumas.

Biomechanics has much to contribute to prosthetics because it is the basis for the construction of prosthetic-orthopedic appliances. Many characteristics of the locomotor apparatus are used to design other technical systems. For example, data on the structure and mechanisms of control of “live kinematic circuits” with many degrees of freedom (for example, the arm, starting from the cleido-scapular joint, has 33 degrees of freedom, which permit a great variety of movements and turns) are used to create automatic manipulators and robots employed in various fields of technology.

Several biomechanical parameters of the circulatory and respiratory systems are considered in diagnosis and in determination of the parameters for operations on the heart and lungs. Research on the biomechanics of respiration and circulation was used to create the “heart-lung” apparatus.

REFERENCES

Sechenov, I. M. Ocherk rabochikh dvizhenii cheloveka. Moscow, 1901.
Lesgaft, P. F. Osnovy teoreticheskoi anatomii, 2nd ed., part 1. St. Petersburg, 1905.
Bernshtein, N. A. Obshchaia biomekhanika. Moscow, 1926. (Contains bibliography.)
Issledovaniia po biodinamike lokomotsii. Edited by N. A. Bernshtein. Moscow-Leningrad, 1935.
Issledovaniia po biodinamike khod’by, bega, pryzhka. Edited by N. A. Bernshtein. Moscow, 1940.
Nikolaev, L. P. Rukovodstvo po biomekhanike ν primenenii k ortopedii, travmatologii i protezirovaniiu (parts 1–2). Kiev, 1947–50.
Legkie: Klinicheskaia fiziologiia i funktsional’nye proby. Moscow, 1961. (Translated from English.)
Weber, W., and E. Weber. Mechanik der menschlichen Gehwerkzeuge. Göttingen, 1836.
Pulsatile Blood Flow. Edited by E. O. Attinger. New York, 1964.
Burton, A. C. Physiology and Biophysics of the Circulation. Chicago, 1965.
Frost, H. M. An Introduction to Biomechanics. Springfield (Illinois), 1967.

V. S. GURFINKEL’

biomechanics

[¦bī·ō·mə′kan·iks]
(biophysics)
The study of the mechanics of living things.

Biomechanics

A field that combines the disciplines of biology and engineering mechanics and utilizes the tools of physics, mathematics, and engineering to quantitatively describe the properties of biological materials. One of its basic properties is embodied in so-called constitutive laws, which fundamentally describe the properties of constituents, independent of size or geometry, and specifically how a material deforms in response to applied forces. For most inert materials, measurement of the forces and deformations is straightforward by means of commercially available devices or sensors that can be attached to a test specimen. Many materials, ranging from steel to rubber, have linear constitutive laws, with the proportionality constant (elastic modulus) between the deformation and applied forces providing a simple index to distinguish the soft rubber from the stiff steel. While the same basic principles apply to living tissues, the complex composition of tissues makes obtaining constitutive laws difficult.

Most tissues are too soft for the available sensors, so direct attachment not only will distort what is being measured but also will damage the tissue. Devices are needed that use optical, Doppler ultrasound, electromagnetic, and electrostatic principles to measure deformations and forces without having to touch the tissue.

All living tissues have numerous constituents, each of which may have distinctive mechanical properties. For example, elastin fibers give some tissues (such as blood vessel walls) their spring-like quality at lower loads; inextensible collagen fibers that are initially wavy and unable to bear much load become straightened to bear almost all of the higher loads; and muscle fibers contract and relax to dramatically change their properties from moment to moment. Interconnecting all these fibers are fluids, proteins, and other materials that contribute mechanical properties to the tissue.

The mechanical property of the tissue depends not only upon the inherent properties of its constituents but also upon how the constituents are arranged relative to each other. Thus, different mechanical properties occur in living tissues than in inert materials. For most living tissues, there is a nonlinear relationship between the deformations and the applied forces, obviating a simple index like the elastic modulus to describe the material. In addition, the complex arrangement of the constituents leads to material properties that possess directionality; that is, unlike most inert materials that have the same properties regardless of which direction is examined, living tissues have distinct properties dependent upon the direction examined. Finally, while most inert materials undergo small (a few percent) deformations, many living tissues and cells can deform by several hundred percent. Thus, the mathematics necessary to describe the deformations is much more complicated than with small deformations.

The biomechanical properties and behaviors of organs and organ systems stem from the ensemble characteristics of their component cells and extracellular materials, which vary widely in structure and composition and hence in biomechanical properties. An example of this complexity is provided by the cardiovascular system, which is composed of the heart, blood vessels, and blood.

Blood is a suspension of blood cells in plasma. The mammalian red blood cell consists of a membrane enveloping a homogeneous cytoplasm rich in hemoglobin, but it has no nucleus or organelles. While the plasma and the cytoplasm behave as fluids, the red blood cell membrane has viscoelastic properties; its elastic modulus in uniaxial deformation at a constant area is four orders of magnitude lower than that for areal deformation. This type of biomechanical property, which is unusual in nonbiological materials, is attributable to the molecular structure of the membrane: the lipid membrane has spanning proteins that are linked to the underlying spectrin network. The other blood cells (leukocytes and platelets) and the endothelial cells lining the vessel wall are more complex in composition and biomechanics; they have nuclei, organelles, and a cytoskeletal network of proteins. Furthermore, they have some capacity for active motility.

Cardiac muscle and vascular smooth muscle cells have organized contractile proteins that can generate active tension in addition to passive elasticity. Muscle cells, like other cells, are surrounded by extracellular matrix, and cell-matrix interaction plays an important role in governing the biomechanical properties and functions of cardiovascular tissues and organs. The study of the overall performance of the cardiovascular system involves measurements of pressure and flow. The pressure-flow relationship results from the interaction of the biomechanical functions of the heart, blood, and vasculature. To analyze the biomechanical behavior of cells, tissues, organs, and systems, a combination of experimental measurements and theoretical modeling is necessary.

Other organ systems present many quantitative and qualitative differences in biomechanical properties. For example, because the cardiovascular system is composed of soft tissues whereas bone is a hard tissue, the viscoelastic coefficients and mechanical behaviors are quite different. Cartilage is intermediate in stiffness and requires a poro- elastic theory to explain its behavior in lubrication of joints. In general, living systems differ from most physical systems in their nonhomogeneity, nonlinear behavior, capacity to generate active tension and motion, and ability to undergo adaptive changes and to effect repair. The biomechanical properties of the living systems are closely coupled with biochemical and metabolic activities, and they are controlled and regulated by neural and humoral mechanisms to optimize performance. While the biomechanical behaviors of cells, tissues, and organs are determined by their biochemical and molecular composition, mechanical forces can, in turn, modulate the gene expression and biochemical composition of the living system at the molecular level. Thus, a close coupling exists between biomechanics and biochemistry, and the understanding of biomechanics requires an interdisciplinary approach involving biology, medicine, and engineering.

biomechanics

The study of the anatomical principles of movement. Biomechanical applications on the computer employ stick modeling to analyze the movement of athletes as well as racing horses.
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