Glossary
of Ergonomic Terms
Ergonomics is the science of fitting jobs to the people
who have to do it, through the design of equipment and procedures. The
word "Ergonomics" comes from two Greek words "ergon",
meaning work, and "nomos" meaning "laws". Today, however,
the word is used to describe the science of "designing the job to
fit the worker, not forcing the worker to fit the job." Ergonomics
covers all aspects of a job, from the physical stresses it places on joints,
muscles, nerves, tendons, bones and the like, to environmental factors
which can effect hearing, vision, and general comfort and health.
The science of ergonomics originated during the Second
World War to overcome performance failures due to human error in new high
tech defense systems. Because of its success, ergonomics is now routinely
applied in the design and development of most military and aerospace systems.
Industrial applications of ergonomics are increasing in response to the
need to improve the productive use of human resources, the quality of
working life and occupational health and safety.
The application of ergonomics ranges from the design of
toothbrushes to the layout of aircraft cockpits, from the design of baby
carriages to wholesale packaging.
People working in ergonomically designed workplaces or
using ergonomically designed products, will tire less quickly, be less
distracted by discomfort and ambiguity, less muddled by confusing displays
and instructions, less frustrated by inconvenience and less stressed by
excessive physical demands. This will mean a lower probability of error,
less likelihood of accidents, less time correcting mistakes and better
morale. It also can mean improved productivity and employee morale. The
cost of ergonomics depends where it is applied. Applied early in the planning
stages, costs will be less: existing budgets will simply be better spent.
Applied as a reaction to serious problems, then costs will be higher.
Anthropometry – the study of human body measurement for use in classification
and comparison.
Awkward Posture – occurs when a joint deviates from the
neutral (natural) position, increasing the risk of injury. Specific movements
are particularly suspect to awkward posture including:
- Flexion
and extension of the wrist (bending up and down)
- Ulnar
and radial deviation of the wrist (side to side movement)
- Abduction
and flexion of the shoulder (upper arm positioned out to the sideor
above shoulder level)
- Elevated
upper extremity (hands at or above shoulder height)
- Flexion
and extension or bending of the neck forward and back
- Side
bending of the neck as when holding a telephone receiver on the shoulder
Biomechanical stressor – the physical aspects of
workstation, tools and work processes that exert stress on the body.
Ergonomics
Program – a systematic process for anticipating, identifying,
analyzing and controlling hazards that can lead to work-related musculosketal
disorders (WMSDs)
Force - The amount of muscular effort required to perform a task. Generally,
the greater the force, the greater the degree of risk. High force has
been associated with Work Related Musculoskeletal Disorders in the shoulder,
neck, the low back, and the forearm, wrist and hand.
NIOSH - National Institute of Occupational Safety and Health. NIOSH is the institution
that provides scientific data upon which OSHA makes recommendations.
OSHA - Occupational Safety and Health Administration. The mission of the Occupational
Safety and Health Administration (OSHA) is to save lives, prevent injuries
and protect the health of America's workers. To accomplish this, federal
and state governments must work in partnership with the more than 100
million working men and women and their six and a half million employers
who are covered by the Occupational Safety and Health Act of 1970.
Recovery
Time - Recovery time is the length of rest between exertions.
Short work pauses can reduce discomfort. Inadequate rest periods between
exertions can decrease performance. As the duration of the uninterrupted
work increases, so does the amount of recovery time needed.
Repetition - Repetition is the number of a similar exertions
performed during a task. A warehouse worker may lift three boxes per minute
from the floor to a countertop; an assembly worker may make 20 units per
hour. Repetitive motion has been associated with injury and worker discomfort.
Risk
Factor (stressor) – a characteristic of the work environment
that research has shown to be associated with an elevated occurance or
severity of WMSD’s. Risk factors can involve purely external exposures
that act on the musculoskeletal system. They can also involve intrinsic
response to a load or task, such as lifiting or rapid and awkward movement.
Static
Postures – postures held over a period of time to resist
the force of gravity or to stabilize a work piece. These postures are
particularly stressful to the musculoskeletal system. Even if there is
some movement, if the joint does not return to the neutral position and
continued muscle force is required, the effect can be the same as a non-moving
posture.
Physiology
and Ergonomic-related Disorders or Injuries
Afferent
nerves – sensory nerves supplying information, including
movement, position, and other sensation, to the central nervous system.
Bursitis – inflammation of the bursae, which are
fluid filled sacs located between skin and bones, or between bones and
the muscles, tendons and ligaments. These fluid filled sacks cushon movement
of one body part over another.
Carpal
tunnel – a narrow anatomic canal or tunnel between the
forearm and the wrist through which the median nerve and nine digital
flexor tendons pass. It is formed by the wrist bones and a dense trans-carpal
ligament.
Carpal
Tunnel Syndrome (CTS) – occurs when the median nerve, which
supplies most of the sensation of feeling to the thumb, index and middle
fingers and half of the ring finger, gets constricted or “pinched”
by inflamed muscles that surround the carpal tunnel. and becomes constricted.
This pinching of the nerve causes numbness and tingling (feeling of "pins
and needles”) in the area of the hand that the nerve goes to.
Cartilage – a thick, white connective tissue that
attaches to the articular surfaces of bones, forming a low-friction cushion.
It is structurally more rigid than tendon.
Cubital Tunnel Syndrome – occurs from a pinched
nerve at the elbow commonly known as the "funny bone". This
might be caused by trauma or repetitive use of the elbow and may be caused
by continuous use of the elbow in a flexed position. This causes the nerve
to become stretched and irritated as opposed to when the arm is extended
and the nerve is in a relaxed position.
DeQuervain’s Disease – a special case of
tenosynovitis that occurs in the abductor and extensor tendons of the
thumb where they share a common sheath. This condition often results from
combined forceful gripping and hand twisting. De Quervain's tenosynovitis
typically causes pain when the thumb is folded across the palm, the fingers
are wrapped over the thumb, and the wrist is forcibly bent towards the
ulna.
Epicondylitis – elbow pain at the site where the proximal flexor or extensor tendons
insert at the lateral or medial epicondyles (bony prominences on the inside
and outside of the elbows).
Humerus – the long bone of the upper arm.
Mechanoreceptors – specialized nerve endings and
sense organs that convey the senses of touch, spatiality, and pressure.
Median nerve – the nerve supplying most of the
sense of sensation to the first through fourth fingers. The median nerve
is the only nerve that passes through the carpal tunnel. It also controls
the working of some of the thumb muscles that permit an individual to
perform a pinch grip. There are other nerves that provide sensation to
the rest of the hand and control other hand muscles, but they do not pass
through the carpal tunnel and therefore are not involved in the carpal
tunnel syndrome. The median nerve is the only nerve that passes through
the carpal tunnel.
Musculoskeletal
Disorders – injuries or illness of soft tissies of the
upper extremity (fingers through upper arm), shoulders and neck, low back,
and lower extremity (hips through toes) that is primarily caused or exacerbated
by workplace risk factors, such as sustained or repeated exertions or
awkward postures and manipulations. Included are disorders of the muscles,
nerves, tendons, ligaments, joints, cartilage and spinal disks. Medical
conditions generally develop gradually over a period of time, and do not
typically result from a single instantaneous event. Examples include Carpal
Tunnel Syndrome, DeQuervains’ disease, Muscle strains, Rotator Cuff
Tendonitis, Synovitis, Tendonitis.
Symptoms
can vary in their severity depending on the amount of exposure the individual
has had. Often symptoms appear gradually as muscle fatigue or pain at
work that disappears during rest. Usually symptoms become more severe
as exposure continues (e.g., tingling continues when at rest, numbness
or pain makes it difficult to perform the job, and finally pain is so
severe that the individual is unable to perform physical work activities).
Examples of symptoms include:
- Decreased
range of motion
- Decreased
grip strength
- Loss of
function
- Deformity
- Swelling
- Cramping
- Numbness
- Burning
- Pain
- Tingling
- Aching
- Stiffness
Repetitive
Strain Injury – injury caused by excessive wear and tear on tendons, muscles,
and sensitive nerve tissues that occurs from continuous use over an extended
period of time.
Synovitis – inflammation of the membranes covering tendon and joint ends.
Synovium – a lubricating tissue located at the sheaths of joints, in bursae
and as the innermost layer of joint capsules. High-usage tendons, such
as the finger flexor and extensor tendons, are also surrounded by lubricating
synovial tissue.
Tendonitis – occurs when tendons become inflamed from repeated tensing. Eventually,
the fibers of the tendon start separating, and can even break, leaving
behind debris that induces more friction, more swelling, and more pain.
Acute tendonitis is caused by overuse, whereas "sub-acute" tendonitis
is more common, and characterized by a dull ache over the wrist and forearm
that gets worse with repetitive activity.
Tenosynovitis – occurs when the tendon sheath thickens
and becomes inflamed from repetitive activity that exceeds the sheath’s
ability to lubricate the tendon. As a result, the area around the sheath
becomes tender and painful.
Tension
Neck Syndrome – a feeling of fatigue or stiffness in the neck, neck pain or headache
radiating from the neck. Signs consist of at least two tender spots or
palpable hardenings.
Thoracic Outlet Syndrome (TOS) – occurs when the
nerves and vessels between the neck and shoulders compress from long periods
of hunching or raising of the shoulders. Symptoms include pain in wrist/hand
and lack of pulse in the affected arm. The last two fingers of the affected
hand may be numb, tingle or turn blue due to a lack of blood.
Trigger
Finger – occurs from a thickening on the tendons responsible for bending
the fingers. These thickened tendons “catch” as they run in
and out of the sheath or a tunnel as the fingers are bent. The most common
cause of this disorder is tenosynovitis.
Ulnar
nerve – an important bundle of sensory and motor nerve
fibers to the arm, and particularly to the hand. Its sensory fibers provide
feeling in the fifth and part of the fourth fingers.
Movements
Radial/Ulnar
Deviation – the bending of the hand at the wrist, toward
or away from the thumb (side to side movement)
Flexion
(flek’ shun) – a bending motion that decreases the
angle between bones, as in bending the fingers close to the hand, or raising
the forearm and hand toward the shoulder.
Extension – a straightening motion that increases the angle between bones,
as in straightening the fingers to open the hand, or moving the forearm
and hand away from the shoulder.
Abduction
(ab-duk’ shun) – movement away from the midline of
the body, as in moving the arms straight out to the sides.
Adduction
(ad-duk’ shun) – movement toward the midline of the
body, as in bringing the arms back to their original position beside the
body.
Rotation – a twisting or turning of a bone on its own axis, as in turning
the wrist from palm up to palm down
Supination
(su-pin-a’ shun) – the act of turning the palm up
or forward
Pronation
(pro-na’ shun) – turning of the palm down or backward
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