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TANGENTIAL. Relating to a straight line that is the limiting through a fixed point.
TASK LOAD. A measure of task severity. Expressed as a stress equivalent (q.v.) which is biomechanically a more accurate measure of task load than measure of metabolic activity, heart rate or pulmonary ventilation.
TENDINITIS. Inflammation of tendon (including tendon sheath) (see TENOSYNOVITIS)
TENDON. Fibrous end section of muscle. It attaches to bone at the area of application of tensile force. When its cross section is small, stresses in the tendon are high, particularly because the total force of many muscle fibers is applied at the single terminal tendon. The site of many industrial diseases caused by trauma, biomechanically improper movements, or failure of lubrication, the tendon must be protected in tool and workplace design. (See TENOSYNOVITIS.)
TENNIS ELBOW. Sometimes called lateral epicondylitis. An inflammatory and/or degenerative reaction of tissues in the lateral elbow region. In an industrial environment it may follow a single, violent effort or repetitive subsymptomatic strain in supination (q.v.) against resistance (as in screwdriving) or violent extension of the wrist with hand pronated. Can frequently be avoided by assuring that the axis of rotation of a tool or machine control coincides with the orthoaxis (q.v.) of rotation of the forearm.
TENOSYNOVITIS. A disease of the tendon sheath, commonly occurring in the fingers, hand, and wrist. The tendon sheath accumulates excessive amounts of synovial fluid with extremely repetitious actions, for example 1500 to 2000 repetitions per hour, which leads to swelling and inflammation of the tendon sheaths. Often associated with continual ulnar deviation (q.v.) of the wrist during rotational movements (e.g., screw driving) or by other overwork and trauma. In industry, extensor sheath inflammation is more frequent. Work tolerance is reduced because of pain during wrist and finger movement.
THERMAL ENVIRONMENT. The surroundings in which a worker is situated which affect his ability to reject or absorb heat. It includes the local temperature, humidity and air velocity. Presence of radiating surfaces also affect the thermal environment. It is significant in the workplace for its effect on work rate, quality control, accidents and physiological well-being (See EFFECTIVE TEMPERATURE.)
THERMAL STRESS. Deviation of an individual's core temperature from it's normal working range caused by extremes in the thermal environment. Can cause changes in body temperature, body chemistry and function of heart, lungs, kidneys and other organs. Influences ability to evaluate sensory feedback as well as many work skills.
THERMODYNAMIC EFFICIENCY. In biomechanics, the ratio of the work performed to the energy consumed by the human body. This is commonly estimated at 20% unless man goes into oxygen debt (q.v.). It is computed by dividing the external work performed (e.g., the number of bricks lifted multiplied by weight and height) by the energy consumption of the human body during the task. Important index for effort rating. (See METABOLISM.)
THERMOGRAPH. A device for producing graphic representation of temperature distribution on the body surface. Commonly an infrared sensor connected to a suitable display device, e.g., video projector, with either graded black-white shades or discrete colors to indicate different temperature levels. Thermographs can accurately indicate local hot spots when such spots are not otherwise readily visible. An important tool in locating excessive work strain and in the maintenance of industrial health.
THEORETICAL BIOMECHANICS. The analytical study of the human body in relation to its immediate mechanical environment. The principles of classical mechanics and the life sciences are employed in the formation of models which predict the effect of mechanical stress on the body. These models can be used as guides in the design of man-equipment interactions such as the workplace and for predictive hypotheses of performance efficiency. In situations where experimentation with man is not feasible, theoretical biomechanics is used to evaluate and predict potentially destructive task situations, e.g., strong vibrations, highway collisions.
TIBIA. The larger of the two bones of the leg below the knee; also referred to as the shinbone. The tibia is the major weight-bearing bone of the leg and transmits forces between the ankle and the knee joint.
TISSUE RHEOLOGY. Study of the deformation and flow of live or excised tissues under external stress. Usually evaluated as a function of time. Can be used to evaluate industrial hardware to avoid stress concentration and instantaneous or cumulative trauma.
TONUS. Commonly known as muscle tone. The tension inherent in muscle which is nominally at rest. A minimal tonus condition is characteristic of healthy muscle. Flabbiness and poor postural control result from poor tonus. Exercise and regular activity aid in maintaining healthy tonus which contributes to worker efficiency.
TORQUE. Refers to the moment of force (q.v.) exerted around any joint during the performance of a task. A moment, or torque, is the product of the perpendicular component of force exerted and the distance from the point of application to the fulcrum or "pivot point" (the joint). Isometric muscle torque which does not result in motion causes high joint forces with physiologic effects dependent on the duration and magnitude of the torque and the joint configuration. E.g., in lifting an object and holding it elevated, torque is exerted by the paraspinal muscles with resultant heavy loads on the lumbar vertebrae. Formerly measured in foot-pounds, inch-ounces, but now in Newton-meters (Nm). If a force, F, acts to produce rotation about a center at a distance, d, from the line in which the force acts, the force has a torque, T = F*d. (See MOMENT OF FORCE (TORQUE))
TRANSVERSE LIGAMENT. There are several transverse ligaments (q.v.) in the body. Usually identified by the local anatomical structure with which they are associated. E.g. flexor retinaculum.
TRANSVERSE PLANE. An anatomical reference plan parallel with the ground (i.e., horizontal) when considering a man in anatomical position (q.v.). Also that plane at right angles to the long axis of an isolated organ. (See SAGITTAL PLANE, CORONAL PLANE.)
TRAPEZIOUS MUSCLE. Broad flat muscle of the upper back. Maintains posture and is an important moving and activating muscle of the shoulder blade. Tasks requiring the worker to hold elbows high will cause fatigue in the trapezius muscle and loss of postural stability. Often the cause of neck pain in these work situations. Important muscle in elevating the arms.
TRAUMA. An injury or wound, generally caused by a physical agent. Cuts, bruises and abrasions are examples of trauma, but trauma may be present even though it is not visible, e.g., strained muscle. The causes of trauma must be anticipated in workplace design or tool design. Protective devices and special clothing (work shoes, gloves) are used to avoid trauma. (See CUMULATIVE TRAUMA).
TRAUMATIC ARTHRITIS. Inflammation, pain and swelling of a joint caused by the application of excessive forces at the joint. Can be triggered by a direct blow or sudden strain and leads to restricted motion. Task design should avoid repeated mild trauma or prolonged strain which can cause traumatic arthritis or exacerbate preexisting arthritic conditions.
TRAUMATIC FIBROSITIS. Inflammation in muscle and increase in fibrous tissues in muscle caused by application of excessive force or by disease. Can result from direct blow or repeated mild trauma at the workplace. Weakness and disability are consequences.
TREMOR. A rapid involuntary alternation of motion of a part of the body. May occur at rest, or only on initiation of movement (intention tremor). Directly caused by alternate rapid contractions of muscle groups and their antagonists (q.v.). Originates from fatigue, disease of nerves or muscles, injury, or response to environment, e.g., shivering from the cold. Presence of tremor disables the worker in precision tasks and increases the risk of accidents.
TRIGGER FINGER. Also known as snapping finger. A condition of partial obstruction in flexion or extension (q.v.) of a finger. Once past the point of obstruction, movement is eased. May occur without apparent cause. A symptom of tenosynovitis (q.v.). (stenosing tenosynovitis creptians). Caused by thickening of a tendon or a localized reduction of the tendon sheath. In the workplace, flexing against strong antagonists and flexing of the distal phalanx (q.v.) without middle phalanx movement is suspected. In addition, tool handles with sharp edges that create local pressure points and localized stress on a particular tendon have been associated with trigger finger. Tool handles should be designed for trigger operation by multiple fingers thereby relieving the stress on a single digit.
TROCHLEA. Bobbin-shaped outcrop of bone at distal end of humerus (q.v.), forming axis shaft of elbow hinge joint, i.e., humero-ulnar joint.
TRIPODAL GRASP. One of the five basic grasps of the hand. Also called manipulative grasp. Object is retained by thumb, index finger an middle finger, which forms a tripod with object possibly in contact with palm. Delicate rotational control is available to the worker for fine screwdriver manipulation, etc.
TUBEROSITY. Large rough outgrowth on a bone which serves as a point of attachment for tendons. It may be used as a convenient anatomical landmark (q.v.), particularly with respect to design of seats and equipment controls.
TUBULAR BONE. Construction of the long bones of the body, e.g., humerus. Provides maximum strength/weight properties while providing centrally located and protected site for blood vessels, nutrients, and bone marrow. Workplace design should avoid imposition of loads with torsional and transverse components.
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