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BASIC GRASP. One of five fundamental means of prehension (q.v.). All activities of grasping and manipulation involve the basic grasps or combinations of them. They are: contact grasp, instrument grasp, power grasp, tripodal grasp and wraparound grasp (q.v.).
BENCHMARK. A reference value against which performance is compared. It may be physiological (e.g., “normal” heartbeat is 60-80 beats per minute) or functional (e.g., “normal” walking speed in industrial work is 2 miles per hour; a worker can assemble 10 parts in an hour). A “normal” electrocardiogram has an acceptable shape; “normal” acceleration signatures (q.v.) of limit movements are characteristically recognizable. Often used in rating. The effectiveness of evaluation procedures in biomechanics often depends on the intelligent selection of bench marks.
BICIPITAL. Relating to the biceps muscle, or the groove in which its tendon lies.
BIFURCATION. A division into two parts or branches; the bifurcations of the arterial tree.
BIOCONTROL SYSTEM. A mechanical system controlled by biological signals; e.g., electromyographically controlled prostheses; e.g., a device alerting truck drivers who are about to fall asleep by means of a bell operated by encephalographic patterns. A biocontrol system should make use of signals of unambiguous meaning which cannot be accidentally generated.
BIOMECHANICAL HYPOTHESIS. An a priori assumption about the operating characteristics of man in a work situation based on functional anatomy. Thus, it might be hypothesized that a task which requires ulnar deviation will limit the rotation of the wrist.
BIOMECHANICAL PROFILE. Electromyographic and biomechanical data recorded simultaneously during motion against a resistance. Included as displacement signature (q.v.), which indicates range and pattern of motion; velocity signature (q.v.), which provides an index of strength and speed of motion; and acceleration signature (q.v.), which shows the quality of motion and is an index of control over precision. Electromyogram of muscle masses involved gives an index of their sequencing and coordination. The profile permits objective evaluation of changes in functional capacity resulting from modifications of man-equipment interfaces. (See ELECTROMYOGRAPHY, BIOMECHANICS.)
BIOMECHANICS. The study of the human body as a system operating under two sets of laws: the laws of Newtonian mechanics and the biological laws of life.
BIONIC DEVICE. Man made device resembling a biological structure in form, mode of operation and function, e.g., space suits, manipulators for radioactive devices, flap-wing aircraft.
BIOTAXIS. Contact with living things. One of the ecological stress vectors. Includes both contact with fellow man, i.e., sociotaxis (q.v.) and with other organisms, e.g., microbiotaxis (q.v.).
BITROCHAL SEAT. Seat designed to fit bitrochanteric width. Anthropometric term roughly synonymous with hip breadth. This dimension is obtained by measurement with calipers applied to the greater trochanter of both femurs in standing position. Important in seat design.
BLOOD PRESSURE. The pressure exerted by blood against containing vascular elements, tissues or the heart chamber, measured in millimeters of mercury above atmospheric pressure. In biomechanics the product of systolic blood pressure and pulse rate, under non-stressful conditions, is considered a good index of physiological work stress and/or the mechanical output of the heart. Together with the pulse beat, it is used as an index of fitness in work. Blood pressure is dependent on the energy of the heart action, the elasticity of the walls of the arteries, and the volume and viscosity of the blood. The maximum (systolic) pressure occurs near the end of the strike of the heart. The minimum (diastolic) pressure occurs late in the ventricular diastole. Note: systolic is derived from the Greek (systole) meaning drawing together or contraction and refers to the contraction or period of contraction of the heart, especially that of the ventricle. Diastolic is from the Greek (diastole) meaning drawing asunder or expansion and refers to the dilation (or dilation period) of the heart, especially of the ventricles, which coincides with the interval between the second and first heart sounds.
BODY-LOAD AGGREGATE. In lifting and manual materials handling, the combined weight of the load manipulated and the body segments involved in the task.
BRACHIALIS MUSCLE. Short, strong muscle originating at lower end of humerus (q.v.) and inserting into ulna (q.v.). Operates at mechanical disadvantage, powerful flexor of forearm, employed when lifting.
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