Z94.2 - Anthropometry & Biomechanics: Biomechanics Section

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MAN-ENVIRONMENT INTERFACE. Region of contact of man with his environment in the performance of a work task. It can include areas of exposure between the worker and the parameters which affect output performance levels such as climate, temperature, and illumination.

MAN-EQUIPMENT INTERFACE. Areas of physical or perceptual contact between man and equipment. The design characteristics of the man-equipment interface determine the transfer of information and motor skill. Poorly designed interfaces with the workplace, machines, tools, fixtures and the workplace may lead to localized trauma (e.g., calluses) or fatigue.

MAN-EQUIPMENT TASK SYSTEM. System where the motor skills of man are matched to those demanded by equipment in such a manner as to facilitate the effective performance of a task. Input-output relations in these systems (i.e. efficiency) are specific and are functions of task design.

MANIPULATION. To operate through the use of the hands. Most industrial tasks involve motor skills of manipulation.

MANIPULATIVE SKILL. The ability to move objects with reference to location in space, speed of movement and control of movement. Manipulative skill depends on intrinsic muscles (q.v.) of the hand and eye-hand coordination.

MAN-TASK SYSTEM. Simple system involving man performing a given task, usually involving only perception and motor skills.

MECHANICAL ANALOGUE. Mechanical model or representation of another type of system (i.e., physiological, anatomical, etc.) which responds to inputs with outputs corresponding to those in the real system.

MECHANORECEPTOR. Sensory end organs receptive to mechanical stimuli, e.g., pressure sensors in the skin. Impairment of mechanoreceptors can lead to degraded quality of work and increased risk at the workplace because of  insufficient sensory feedback (q.v.). Control in manipulation of tools or objects depends on effective mechanoreceptors.

MECHANOTAXIS. Contact with a mechanical environment consisting of forces (pressure, moment), vibration, etc.  One of the ecological stress vectors. Improper design of the mechanotactic interface may lead to instantaneous trauma, cumulative pathogenesis, or death.

MEDIAL DISPLACEMENT. Movement of a limb or body segment toward the mid-sagittal plane (q.v.). Bringing the legs or arms together are examples of medial displacement. (See LATERAL DISPLACEMENT.)

MEDIAL POPLITEAL NERVE. Important nerve at the back of the leg in the hollow of the knee. (See popliteal region.) Pressure on the medial popliteal nerve caused by poor seat design may lead to inadequate blood flow to the feet.

MEDIAN NERVE. A major nerve controlling the flexor muscles (q.v.) of the wrist and hand. Tool handles and other objects to be grasped should make good contact with the sensory feedback (q.v.) area of this nerve located in the palmar surface of the thumb, index, middle, and part of ring finger.  It is the median nerve which is compressed in carpal tunnel syndrome.

METABOLIC COST. The amount of energy consumed as the result of a specific activity, generally stated in calorie (q.v.) units. Can be measured by spirometry (q.v.) or respiratory gas exchange. A helpful measure of task severity. (See METABOLISM, LIGHT TASK.)

METABOLIC RATE. Rate of energy consumption required for performance of body activities. Basal metabolic rate is the minimum rate at which vital body functions can be maintained. Units are in calories per unit time. Metabolic rate can be determined indirectly by oxygen uptake or carbon dioxide discharge and is a good index of work strain of steady state work when work is medium- heavy or heavy, and large muscle masses are involved.

METABOLISM. The physiological combustion process. Conversion of food stuffs into body tissue, energy, and waste products. A continuous complex process influenced by the energy demands of the body as well as its state of health, temperature, emotion, etc. (See AEROBIC METABOLISM, METABOLIC RATE, METABOLIC COST.)

METACARPAL BONES. The five bones in the hand which connect the carpal (wrist) bones with the phalanges (knuckles). The metacarpals form the structural base of the palm of the hand.

MICROBIOTAXIS. Contact with microorganisms. Exposure to an environment of certain microbes. One of the ecological stress vectors. A form of biotaxis (q.v.).

MICROMOTION FILM. Motion picture or video tape made of a specific job or class or work. Each component of the task is portrayed on a single frame for independent study. With such films exposed at fast speeds (frames/ sec), it is possible to break down complex motion patterns into their most basic elements for therblig determination and efficiency analysis. In biomechanics this technique is used to identify short duration acceleration patterns and reflex responses, e.g., during lifting, which are too fast for visual observation.

MID-SAGITTAL PLANE. A reference plane formed by bisecting the human anatomy so as to have a right and left aspect. Human motor function can be described in terms of movement relative to the mid-sagittal plane. (See TRANSVERSE PLANE, CORONAL PLANE.)

MOMENT OF FORCE (TORQUE). The effectiveness of a force to produce rotation about an axis measured by the product of the force and perpendicular distance from the line of force to the axis. (Sl unit is Nm.) Popularly it refers to the twisting or turning effect of a force. Moments, like forces, have both internal and external effects upon the body in which they are acting. The external effect of a moment on a body is to change or attempt to change the angular or rotational velocity of the body. The internal effects of moments are to cause a state of strain. A moment is necessary to produce angular acceleration. (See TORQUE.)

MOMENT CONCEPT. The concept based on theoretical and experimental bases that lifting stress depends on the bending moment exerted at susceptible points of the vertebral column  rather than depending on weight alone.

MOMENT OF INERTIA. The inertial resistance to a change in rotational motion which must be overcome by a torque (q.v.), in order to produce angular acceleration. It is a function of the distribution of mass about the axis of rotation.


MOTIONS PATHWAY. The locus of travel of an anatomical landmark, often a "knuckle," in moving from one point of the workplace to another. It includes the elemental increments of "reach" and "move" as defined by the various predetermined motion time systems (q.v.) and can also include such motor therbligs as "position," "examine," "hold," etc. motion time methods system, Abbreviated MTM. (See PREDETERMINED MOTION TIME SYSTEM.)

MOTOR NERVE. A nerve also known as an efferent nerve which conducts impulses from the brain or spinal cord to muscle.

MUSCULOSKELETAL SYSTEM. The combined system of muscles and bones which comprise the internal biomechanical environment.


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