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Z94.2 - Anthropometry & Biomechanics: Biomechanics Section

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PALMAR ARCH. Blood vessel in the palm of the hand from which the arteries supplying blood to the fingers are branched. Pressure against the palmar arch by poorly designed tool handles may cause ischemia (q.v.) of the fingers and loss of tactile sensation (q.v.) and precision of movement.

PARTICULOTAXIS. Contact with particulate matter. One of the ecological  stress vectors. Particulotaxis at the workplace has caused numerous industrial diseases such as silicosis, which is commonly called potter's consumption or stonemason's disease, berylliosis, which results from exposure to beryllia dust, and black lung disease found among coal miners. Ventilation, electrostatic percipitators, proper work clothes, makes, etc., can effectively abate the dangers of particulotaxis.

PATHOCUMULUS. Trauma resulting from repetitive application of work stress.

PATHOLOGICAL PROCESS. Any process which causes temporary or permanent changes in physiological function or anatomical structure resulting in a state of disease. Pathological processes may be triggered or exacerbated by poorly designed man-task interfaces.

PERIPHERAL HEMODYNAMICS. The study of blood flow phenomena in the outer regions of the body. Because work tasks involve the extremities, knowledge of peri-pheral hemodynamics is necessary to understand the interaction of internal and external environments (q.v.)

PHALANX. Colloquially known as the knuckle, any of the long bones of the fingers or toes. Frequently used as anatomical reference points (q.v.) in work analysis.

PHARMACOKINESIS. Motions caused by the administration of drugs.

PHRENIC NERVE. Motor nerve to the diaphragm, originating from the vertebral column in the neck and transversing the thoracic cavity. Important in diaphragmatic respiration. Can be  irritated in the neck by a poorly designed seat harness. Repeated pressure surges in the abdominal cavity caused by movement of the back required by improper seat height are transmitted to the diaphragm and may cause pain to be projected to the shoulder.

PHYSIOLOGICAL OPTIMAL ALIGNMENT. Alignment of the principal axis of rotation of a task with the orthoaxis of a limb. For most tasks, the physiological optimal alignment is not a fixed position due to variations between the individuals.

PHYSIOLOGICAL RESPONSE. Any of the body's reactions (hormonal, electrochemical, muscular, or nervous, etc.) to any internal or external stimulus. Physiological response to external stress is synonymous with work strain (q.v.).

PHYSIOLOGY. The study of the biological, biochemical and biophysical functions of living organisms. It is one of the basic disciplines in the practice of biomechanics.

PIEZOELECTRIC EFFECT. A property exhibited by certain crystalline substances in which the application of mechanical stress produces a redistribution of electric charge and the application of a voltage produces a mechanical deformation. This property is exhibited by bone and other tissue.

PINCH GRASP. Also known as key grasp. One of the lesser used grips of the hand. Involves the thumb and the near side of the index finger at the second phalanx (q.v.). Not a natural grip, it must be learned and requires high levels of manual dexterity and tactile discrimination. Used to apply large forces to small objects because of the strength of the thumb.

PIVOT JOINT. A joint in which motion is limited to rotation about an axis perpendicular to the contact surface. The atlas and axis, the two uppermost vertebrae, form such a joint which accommodates rotation of the head. Attempts at movement other than pure rotation at such joints may be dangerous or cause discomfort.

PLANTAR FLEXION. The motion about the ankle joint which raises the heel from the ground and points the toe, e.g., standing on toes, operating a gas pedal.

PLAY FOR POSITION. One of the fundamental motions or the therbligs at the workplace. The pre-positioning of an object for subsequent operation. Mechanical guides aid in playing for position.

PNEUMOTACHOGRAPH. An instrument used to record the rate of breathing and pulmonary ventilation (q.v.). Designed by Wolff, it is commonly used in work physiology, especially in agriculture, forestry, and foundry work.

POLYGRAPH. Recording instrument used to monitor and detect changes in physiological systems (e.g., sweat rate, heart rate, respiratory rate, etc.) simultaneously. It  is generally used for work physiological measurements but its popularity is derived from its association with lie-detecting tests.

POSITIVE WORK. Work performed by a person in applying a force through a distance. Muscular effort consists of generating the energy to perform work in the true engineering sense. Work stress (q.v.) and strain (q.v.) (muscular shortening) are necessary corollaries of positive work. It is one of the elements of a lifting task (q.v.). (See NEGATIVE WORK, ISOMETRIC WORK.)

POSTPRANDIAL. Literally after meal. Its importance in the industrial workplace is in understanding the effect of digestion upon work performance. Basically, the consumption of food in substantial quantities causes a shift in the flow of blood away from the skeletal muscles and peripheral organs and toward the viscera, severely limiting metabolic activity of the skeletal muscles. Also, after heavy meals a lower level of alertness and a greater accident proneness may exist. Indication of pre or post prandial state of subject should be included in work-task study. 

POWER GRIP.  One of five basic grasps of the hand. It consists of the fingers wrapping around the gripped object with the thumb placed against it. This allows use of the strong opposing muscles of the thumb and the combined strength of the finger flexor muscles. Used in hammering operations,  with special pliers, and handbrake applications. The tool designer should be aware of the strength available from this grip.

PREDETERMINED MOTION TIME SYSTEM. Any scheme useful in the prediction of performance times of industrial work tasks. It analyzes all motions into elemental components whose unit times have been computed according to such factors as length, degree of muscle control required, precision, strength, etc. Time standards of several of these are used as bench mark (q.v.) levels for normal performance in biomechanics and work physiology. For these purposes they are divided into systems: derived from taxonomy and kinesiology; non-taxonomic and kinesiological; taxonomic but non-kinesiological.

PREHENSILE. Adapted for taking hold. Usually refers to grasping motions of the hand. The prehensile and manipulative (q.v.) ability varies considerably with levels of training and cultural and social background. Performance of workers on a given task may differ for these reasons. (See GRASP REFLEX.)

PREHENSION. Refers to the ability to grasp or take hold. (See PREHENSILE.)

PRESSURE SENSOR. One of the sensory end organs (q.v.) responsive to a pressure stimulus. Important for tactile control (q.v.). Feedback from pressure sensors between fingers enables the worker to moderate his grasp. Interference with pressure sensor function, as with heavy gloves or shoes, will impair touch perception and may cause faulty grasp or insufficient foot pedal control.

PRIME MOVERS. The muscles which produce or maintain a specific motion or posture. Also called agonist, they are assisted by synergists (q.v.) and opposed by antagonists (q.v.). Prime mover activities may be preceded by action of a trigger muscle initiating the movement. Knowledge of the prime movers is essential in workplace design and in electromyographic evaluation of task severity.

PRONATION. Rotation of the forearm in a direction to face the palm downward when the forearm is horizontal or backward when the body is in anatomical position (q.v.). An important element of industrial demanded motions inventory (q.v.), it is performed by muscles whose efficiency is a function of arm position. (See RANGE OF FOREARM PRONATION AND SUPINATION.)

PROPRIOCEPTION. The sensing of one's location relative to the external environment. An important sense for maintenance of balance and for orienting one's self for performing work tasks. An impaired proprioceptive sense can cause industrial accidents or faulty performance where controls are located outside the visual field.

PROSTHESIS. The replacement of a body part. The replacement may be for a limb, a blood vessel, an organ, or a skeletal member. It may be partially or completely nonfunctional when external, although it is usually cosmetic. (See ORTHOSIS.)

PROXIMAL. Describing that part of a limb, body segment, or muscle which is closest to the point of attachment. The elbow is proximal to the wrist which is proximal to the fingers. Generally refers to distance from trunk.

PSYCHOSOMATIC RESPONSE. A physical or physiological response resulting from psychological stimulus. Often a defensive reaction. Important to understand in the practice of human engineering (q.v.) and in modifying sociotaxis (q.v.) in ergonomic analysis (q.v.).

PULMONARY VENTILATION. Commonly referred to as breathing. Volume of respiratory gases passing in and out of the lungs per unit time. Used in spirometry (q.v.) as in index of work stress (q.v.).

PULSE RATE RATIO. The ratio of pulse rate after or during exercise to pulse rate at rest. Typically used as a measure of heart function, the pulse ratio is also used as a measure of work stress.

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