Z94.2 Anthropometry & Biomechanics: Biomechanics Section
The Biomechanics subcommittee acknowledges the efforts of previous subcommittees in establishing a substantial base for this chapter. Our task was facilitated greatly by these previous subcommittee members. Many of the terms developed by these people have been retained because we could not improve them. There are too many previous committee members to mention here. However, they are identified in previous editions of this book.
The present Biomechanics Subcommittee members have updated and revised many of the terms relating to biomechanics. They have made substantial contributions, which cannot be diminished by the use of previous editions of this chapter. The subcommittee consists of the following members.
Sudhakar L. Rajulu, Ph.D
Lockheed Engineering & Sciences Co.
Jeff Poliner, M.S.
Lockheed Engineering & Sciences Co.
Lara Stoycos, M.S.
Lockheed Engineering & Sciences Co.
Human Factors and Ergonomics Section
Steven A. Lavender, Ph.D.
Rush-Presbyterian-St. Luke's Medical Center,
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ABDOMINAL WALL. The covering of the abdominal cavity composed of skin, fatty tissue, muscles and fibrous structures. Extends from the rib cage to the pelvis. The muscles of the abdominal wall assist in respiration and in the maintenance of posture. The workplace should not mechanically press against the abdominal wall.
ABDUCTION. Deflection of a limb away from a sagittal plane (q.v.). A basic element of motions inventory. (See ADDUCTION.)
ABDUCTORS. Muscles which, by contraction, effect abduction of a limb. E.g., the deltoid (q.v.) abducts the arm,
ACOUSTIC STIMULUS. Sound signal which indicated that an individual is to initiate, maintain, or terminate an activity.
ACROMION. A bony outcrop of the shoulder blade which forms a joint with the collarbone and is attached to the deltoid and trapezius muscles. It can be felt through the skin in front of the shoulder. It is used as an anatomical reference point (q.v.) in anthropometry (q.v.).
ACTION POTENTIAL. Electric activity produced in nerve, muscle or other excitable tissue during activity. Once the threshold of stimulation is reached, the action potential is triggered and the "all or none law" (q.v.) applies. Most electrophysiological recordings are produced by conditioned signals evoked originally by action potentials, e.g., electrocardiograms, electromyogram.
ACTIVATING RECEPTORS. End-organs of nerves which trigger a specific response reaction upon receipt of a stimulus. (See SENSORY END ORGANS.)
ADDUCTION. Movement of a limb towards the mid-sagittal plane (q.v.). (See ABDUCTION.)
ADDUCTOR. Muscle which by contraction causes adduction of a limb. E.g., pectoralis major adducts the arm and the abductor magnus adducts the thigh.
AEROBIC METABOLISM. Physiological "combustion" of body fuels with oxygen in muscle during exertion. This is a highly efficient form of energy release available for long periods of time in light and medium work. During heavy work aerobic muscle metabolism is preceded by anaerobic (q.v.) muscle metabolism as aerobic metabolism takes several minutes to be initiated.
AFFERENT. Conveying a stimulus or a body fluid inwardly towards a biological processing station (See EFFERENT.)
AGONIST. (See PRIME MOVERS.)
AIRWAY. The path that air of other respiratory gases take in going from the mouth or nostrils, to the alveoli.
AIRWAY RESISTANCE. The resistance, usually measured as a pressure drop, which must be overcome for air to flow through the airway.
ALKALOSIS. A pathological condition in the body of excessive base or below normal acids. One occupationally important cause is hyperventilation (q.v.), which may result from anxiety, drugs or disease or from bad environmental factors such as high temperature, high concentration of solvents or too rapid or heavy a work rate. Physiological response is evidenced in respiratory rate, cardiac rate and kidney function, or it may cause fainting.
ALL OR NONE LAW. Nerve fibers and associated muscle fibers respond entirely to a stimulus or do not respond at all. In muscle, strength of contraction is governed by the number of fibers stimulated and the frequency of stimulation; it is not determined by the individual fiber, which, once stimulated, cannot be stopped halfway in its contractile element, but is limited by its elasticity.
ANAEROBIC METABOLISM. An energy generating process within the body that occurs without the presence of oxygen. Occurs when energy demand of a task exceeds energy available by aerobic metabolism (q.v.) due to inadequate supply of oxygen in a muscle This results in a state of "oxygen debt" where body fats are "burned" without the use of oxygen. This is a low efficiency process because the anaerobic combustion products must be removed from the body by a secondary aerobic process occurring after the activity has finished. Hence, man pants after heavy exercise. Anaerobic activity should be minimized in task design. There must be a payback for any anaerobic effort.
ANALYTIC WORKPLACE DESIGN. Based on established biomechanical and behavioral concepts including the known operating characteristics of man. Produces a workplace situation well within the range of human capacity and does not generally require modification improvement, or preliminary experimental "mock-ups."
ANATOMICAL POSITION. Subject standing erect against a wall with feet parallel and touching, arms adducted (q.v.) and supinated (q.v.), with palm faced forward. Used as a reference posture in anatomical description.
ANATOMICAL REFERENCE POINT. A prominent structure or feature in anatomy which can be located and described by visual inspection or palpation of the body surface. Movements and postures are often defined by description of the relative position and displacement of various anatomical reference points with respect to each other. Also known as anatomical landmark.
ANATOMY. The discipline dealing with the geometrical and topographical description of the structures of the body. It includes description of the structures such as bones, muscles, blood vessels and nerves, including the shape and dimensions (gross anatomy) as well as description of the finer features of human tissues visible only through the microscope (histology). Since structure determines function, a knowledge of anatomy as the structural basis of human performance is indispensable for the proper understanding of human function. It is both static and dynamic.
ANATOMY OF FUNCTION. A subdiscipline of kinesiology (q.v.) which describes changes in the configuration of limbs during the performance of task. Different from "functional anatomy" (q.v.) which relates to physiological function.
ANGLE OF ABDUCTION. Angle between the longitudinal axis of a limb and a sagittal plane (q.v.).
ANGULAR ACCELERATION. The time rate of change of the angular velocity.
ANGULAR VELOCITY. The time rate of change of an angular measure.
ANISOTROPIC. Indicating nonuniform directional physical properties. Body tissues such as bone are anisotropic. The strength of bone differs in different directions. Muscle also has highly directional properties.
ANOXIA. Lack of oxygen in the blood stream or tissue cell. Although the result of many mechanisms, the ultimate effect frequently is defective function of many sensory and motor functions. Produced environmentally by high altitude, chemically by pollutants and drugs, or locally by overexertion. May result in death.
ANTAGONIST. A muscle opposing the action of another muscle. An active antagonist is essential for control and stability of action by a prime mover (q.v.) E.g., the biceps are antagonistic ti the pronator during forearm pronation.
ANTHROPOMETRIC TABLES. An arrangement of tabulations and dimensional drawings stating human body measurements. Good quality tables stress data in ranges of dimensions ascribed to certain percentiles of the population rather than listing of mean values. Anthropometric tables are essential to analytical workplace design (q.v.). (See ANTHROPOMETRY.)
ANTHROPOMETRY. The study of people in terms of their physical dimensions. It is the formal name for the technique used to express quantitatively the form of the human body.
ANTHROPOMORPHIC. Shaped like man or man's limbs. Mechanical manipulators and bionic devices often have anthropomorphic features. Cosmetic prostheses are anthropomorphic.
APPLIED ANATOMY. A subdiscipline of anatomy dealing with problems involving physical (as opposed to physiological) function of body systems. The term is sometimes also used to indicate the application of anatomical principles to specific fields of human activity such as surgical anatomy, diagnostic anatomy, anatomy of work.
APONEUROSIS. A fibrous sheet of connective tissues which serves as attachment of muscles or muscle fibers at origin or insertion on bone; an expanded tendon. It is normally pressure resistant and is a preferred load-bearing site. E.g., the seat back should support the aponeurosis of the latissimus dorsi (q.v.). It does not have the elastic properties of the muscles attached to it.
ARM-TOOL AGGREGATE. The arm holding and manipulating a tool, acting with the tool as an integral biomechanical unit. In estimating physiological work, the arm-tool aggregate mass must be considered.
ARTHRITIS. Inflammation of joint structures. Such inflammation may or may not cause pain, and may result in joint destruction and/or limitation of motion. Important cause of partial occupational disability, manipulative limitations, and reduced capacity for head scanning, and increases with aging.
ARTICULATION. Refers to the junction of bones and ligaments which allow body motion. Commonly known as a joint. e.g., knee, elbow. The wrist is the articulation between forearm and hand. (See JOINT.)
ASTHENIA. Lack or loss of strength and energy. When pertaining to somatotype (body build), refers to condition of very slender, feeble-appearing person.
ATROPHY. Wasting away of body tissues or organs from disuse, poor nourishment, or from disease, leaving decreased mass of muscle.
AVAILABLE MOTIONS INVENTORY. The nature and quality of motions which are available from man in the performance of a specific task. It may be limited by physiological or anatomical deficiencies of individuals.
AXIS OF ROTATION. The true line about which angular motion takes place at any instant. Not necessarily identical with anatomical axis of symmetry of a limb nor necessarily fixed. Thus, forearm rotates about an axis which extends obliquely from lateral side of elbow to a point between the little finger and ring finger. The elbow joint has a fixed axis maintained by circular joint surfaces, but the knee has a moving axis as its cam-shaped surfaces articulate. Axis of rotation of tools should be aligned with true limb axis of rotation. Systems of predetermined motion times often specify such axes incorrectly. Almost all joints move through multicentric axes.
AXIS OF THRUST. Line along which thrust can be transmitted safely. In the forearm it coincides with the longitudinal axis of the radius. Tools should be designed to align with this axis. Ulnar or radial deviation which produces misalignment causes bending stress acting on the wrist.
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