Ergonomics Glossary
Some common ergonomics-related words, terms, and concepts are defined and explained below.
[A] [B] [C] [D] [E] [F] [G] [H] [ I ] [J] [L] [M] [N] [O] [P] [R] [S] [T] [U] [V] [W]
[A]
Administrative Control:
Work practices, work methods, policies and procedures established by the
employer with the goal of reducing exposure to a work-related risk / hazard.
Ear plugs are an administrative control to reduce the risk of hearing loss.
Some administrative controls designed to reduce the risk of WMSDs include:
scheduling more rest breaks, job rotation schemes, worker training, etc.
Anti-fatigue mats:
Shock absorbing mats made of rubber, foam, visco-elastic material, or a
combination of these. The mats are placed on hard floor surfaces (metal,
concrete, etc.) in areas where people stand for prolonged periods or repeatedly
walk a short distance back and forth. The mats help to reduce fatigue and
discomfort associated with standing / walking on hard surfaces.
Anthropometry:
The study and measurement of human physical dimensions. It is a branch of
the human sciences that deals with the measurements of body size, shape,
strength and working capacity.
Awkward Posture:
Any fixed or constrained body position that overloads muscles, tendons,
or joints. Generally, the more a joint deviates from the neutral position
the more the posture is considered to be awkward and the greater the risk
of injury.
[B]
Biomechanics:
The study of the effects of internal and external forces on the human body
both in movement and at rest. Biomechanical models calculate the levels
of force (compression and shear) and torque that the joints, tendons, muscles,
and ligaments are required to withstand and/or generate. The calculated
forces and/or torques are compared to recognized limits to evaluate the
acceptability of a task, activity, etc.
Bursitis:
Bursae are lubricating, fluid filled pads that separate tendons from bones
in some joints of the body (e.g. shoulder). Bursitis is the result of the
inflammation of a bursae. The inflammation may be caused by repetitive and/or
forceful exertions at the joint.
[C]
Carpal Tunnel Syndrome (CTS):
A specific medical diagnosis for one type of WMSD. Carpal Tunnel Syndrome
is a disorder of the hand and wrist that is caused by the compression of
the median nerve where the nerve passes from the forearm, through the carpal
tunnel in the wrist and into the hand. as the nerve Symptoms can include
tingling and numbness in the hand, and loss of dexterity and strength in
the hand.
Circadian Rhythms:
Cyclic changes in physiological variables, or biological rhythms, can vary
in terms of their period (time to complete one cycle). A large number of
biological rhythms have a period that is close to 24h, and these are referred
to as circadian rhythms. Literally, circadian means “about a day.”
Contact Stress:
Exposure of a body part to a hard or sharp surface/edge from a workstation
or a hand tool, e.g. leaning forearms against the sharp edge of a desk/table.
Contact stress has been associated with the development of some WMSDs.
Control/Display Relationship:
This refers to the degree to which relationships between controls and displays
are consistent with our expectations. We all have expectations concerning
the movement of a control and its expected effect on a display/device (e.g.,
when we turn a volume knob to the right we expect the volume to increase,
if we turn a knob to the right we expect a pointer in the related gauge
to increase (move up / move to the right)).
Cumulative Trauma Disorder (CTD):
A term, typically used in the United States, used to describe work-related
injuries to the muscles, tendons, or nerves. Term implies that the injury
is the result of a build up of trauma over a period of time which may or
may not be the case. WMSDs is the term preferred by Ergonomists.
Cycle:
A time interval during which a regularly recurring sequence of events is
completed. It an be the time to complete a task with many elements or the
time to complete a single operation in a repetitive task.
[D]
Deviation:
A term used to describe the movement of a body part away from the neutral
position of that joint or limb. Typically used to describe wrist positions.
Ulnar deviation is the movement of the wrist away from neutral, towards
the little finger. Radial deviation is the movement of the wrist away from
neutral, towards the thumb.
Duration:
Duration mean different things under different circumstances. Typically,
duration will refer to the length of time a person performs a task, or is
exposed to a specific risk factor, without a period of rest. It may, however,
be used to describe the amount of time during a shift a task is performed
(e.g. 4 hours per shift). Duration may also be measured in seconds or minutes
when describing the amount of time a person will exert a forceful effort
(e.g. when gripping a tool or performing a pinch grip). Generally speaking,
the longer the duration of exposure to a risk factor the greater the likelihood
of a negative outcome.
Dynamic muscle work:
Use of muscles to generate force such that the length of the muscle changes
during the activity, resulting in motion around a joint.
[E]
Endurance:
Endurance is the ability to continue to work, or in the static case, to
continue to maintain a posture or position. It is the maximal amount of
time a person can perform useful work and it is related to the amount of
effort being exerted (i.e. amount of muscular or aerobic / anaerobic effort).
Energy Expenditure:
The amount of energy (power) used by the body at any point of time... at
work or at rest. It is usually expressed in terms of kilocalories per minute
(kcal/min) or in terms of the amount of oxygen used (litres of O2).
Ergonomics:
Ergonomics (or human factors) is the scientific discipline concerned with
the understanding of interactions among humans and other elements of a system,
and the profession that applies theory, principles, data and methods to
design in order to optimize human well-being and overall system performance.
[F]
Fatigue:
Fatigue is a loss of work capacity resulting from preceding work. It is
usually associated with a loss of efficiency and reduced capability. Fatigue
is both a physical and a psychological state.
Force:
Force can either be applied by the body (i.e. through muscular effort) or
to the body. When doing 'work' the body uses muscles to generate force to
allow for movement of body segments, to resist the 'force' of objects being
lifted / carried, or to apply force to an object to move it. When your muscles
contract they also generate 'reaction' forces in the body at the joints
(e.g. shoulder, vertebrae, etc.). Force can also refer to the amount of
force that is applied to the body from an external source. When using a
pair of pliers the handles of the pliers press into the palm of the hand.
When resting the forearm on the edge of the desk the desk exerts force on
the muscles, nerves, and blood vessels in the forearm.
Frequency:
Frequency, in ergonomics terms, refers to how often we repeat / do something.
The 'units' of interest for frequency will vary depending on the task being
looked at. For many repetitive type tasks we are interested in looking at
frequency in terms of the number of repetition / actions per minute. In
the case of an office worker we may be interested in knowing how many times
per hour the worker gets up out of their chair. Or, we may want to know
how many times a shift a certain action or task is performed. (See Repetition)
[G]
Glare:
There are two sorts of glare – discomfort glare and disability glare.
The mechanisms of both are unknown, but the conditions under which discomfort
glare occurs and the ways in which disability glare can affect performance
are well known.
- Discomfort glare: When a portion of the visual field has a much higher luminance than its surround, a feeling of discomfort around the eyes and brow may occur. This increases with an increase in the luminance of the glare source, and with an increase in the angular size of the glare source at the eye, and decreases with an increase in the luminance of the background and with an increase in the angular position of the source relative to the line of sight.
- Disability glare: An extraneous light source can affect visual performance. The problem with disability glare is that it reduces contrast, causing a washing out – the whole scene looks grey. Like discomfort, the disability glare is often reduced by increasing the light level. Think about a car’s headlights on full during the day; there’s lots more light, and as a result, the car’s headlights are less of a problem.
Grasp / Grip:
The way we grip objects makes a big difference in how much effort we must
use to hold and manipulate the object. There are two main types of grasps
of interest. The power grasp / grip is one where we can wrap our fingers
and thumb around the object as when picking up a suitcase handle or grasping
a hammer. The other type of grasp is a pinch grasp / grip. There are in
fact a number of different types of pinch grips. The one we most commonly
think about is the one where we pick up / hold something by pinching it
between the thumb and fingers (e.g. when picking up a pen from a flat surface).
Other types of pinch grips are used:
- when holding / using a pen,
- when picking up a flat surface between the thumb and the out stretched fingers,
- when just wrapping the fingers around the edge of a flat surface and pinching it against the palm and base of the fingers, and
- when picking up something with a wide 'pinch' grip (i.e., fingers and thumb spread wide apart as in picking up the end of an apple juice can).
[H]
Hand-Arm Vibration:
Vibration applied to the hand/arms through a tool or piece of equipment.
Hand-Arm Vibration Syndrome (HAVS):
HAVS, also known as Raynaud's Phenomenon and Vibration White Finger, is
a chronic disorder that can develop when the hand is subjected to repeated
and prolonged exposure to vibration, often resulting in irreversible damage
to the blood vessels, nerves and muscles. Symptoms include tingling or numbness
in fingers; painful spasms of the hand' blanching of one or more fingers;
and eventual loss of sensation and control in the fingers and hands.
Hazard:
Any condition, situation, physical property or action that may result in
illness, injury or other negative outcome. Also, a p otential source of
physical injury and/or damage to the health of people or damage to property
or the environment.
Human factors:
Human factors is considered to be synonymous with ergonomics, however it
is essentially an American term, having its scientific roots grounded in
psychology, whereas ergonomics which, as a science/practice, was formalized
after WW2 in Britain, considers a very broad range of sciences (e.g., anatomy,
psychology, physiology, industrial medicine, design, architecture, illumination
engineering, etc.)
[ I ]
Interaction of risk factors:
The risk factors for many types of injuries and accidents are not separate
and singular. Typically there are a number of risk factors that can contribute
to an injury or accident and it is common for these risk factors to interact
to greatly increase the likelihood of the injury or accident. When exposed
to more than one risk factor for any negative outcome the final risk to
the worker will be much higher than might be found by just adding the level
of risk for all factors together. For instance, one study found that the
odds of developing a WMSD were 6 times greater if a job was highly repetitive,
3 times greater if a job required the exertion of high grip forces, but
29 times greater if the job had both high repetition and high force requirements.
[J]
Job enlargement:
Job enlargement is the name given to the process of extending the work cycle
by adding related tasks to the job description. An example might be to involve
the workers in cleaning, and maintaining their own plant, and perhaps also
to obtain their own materials from a central store, thereby doing tasks
that were once done by service departments. Like job rotation, job enlargement
introduces variety.
Job enrichment:
This is the process of providing workers with greater responsibility for
their work output. It can be accomplished by perhaps having them do their
own QC and making them responsible for basic maintenance. It is also important
to recognize achievement and to give due recognition of a job well done.
Job rotation:
Job rotation is where workers perform a variety of different, not necessarily
related jobs during their work day / shift. A good job rotation scheme will
be designed to allow each worker to be exposed to a variety of physical
and mental demands during the shift.
Job Satisfaction:
A multi-dimensional psychophysical measure that compares a person's opinions
about job requirements to individual goals for meaningful work.
[L]
L5/S1:
The joint between the 5th lumbar (L5) and 1st sacral (S1) vertebrae of the
spinal column. Many low-back disc injuries occur at this joint.
Ligaments:
Fibrous structures that connect bones to bones, providing support while
allowing flexibility and movement.
[M]
Manual Material Handling (MMH):
Any handling task involving the human body as the main "power source".
MMH includes lifting, lowering, pushing, pulling, carrying and holding.
Maximum Voluntary Contraction (MVC):
The maximum force a muscle can generate, voluntarily, during a static contraction.
Job tasks may be classified according to what percentage of the workers
MVC (%MVC) is required to perform a task. The higher the %MVC the greater
the risk of fatigue and/or injury.
Median Nerve:
A large / main nerve that runs from the shoulder, through the arm and forearm
into the hand. The median nerve passes from the forearm to the hand, via
the wrist through the carpal tunnel. This nerve supplies the sensation of
temperature, touch and pain to the thumb and first three fingers of the
hand. It also supplies various small muscles for the fingers and thumb.
(See Carpal Tunnel Syndrome).
Monotony:
A lack of variety, sameness; sometimes applied to highly repetitive tasks
that require little decision making and that might be done better by machines.
Also applies to tasks that require prolonged monitoring of computer and
other process control systems.
Musculoskeletal System:
The bones, muscles, tendons, ligaments, and joints in the body and how they
interact with each other.
[N]
Neutral Position:
The body position which minimizes stresses on the body. Typically the
neutral posture will be near the mid-range of any joint’s range of
motion.
NIOSH:
The US based National Institute for Occupational Safety and Health. The
researchers at NIOSH have developed and revised a well-accepted method for
assessing lifting and handling tasks (i.e. the NIOSH Equation).
[O]
Oxygen Consumption:
The rate at which the body's tissues and cells use oxygen; measured as the
amount of oxygen entering the body minus the amount leaving. Physical workload
is assessed by measuring oxygen consumption in litres of O2 per minute.
[P]
Percentile:
Used to express the variability of any given measure. Percentiles represent
percentages of a sample with a value of x or less. For instance, a 90th
percentile measurement will mean that 90 percent of the population are below
that level and 10% of the population are above that level. This term is
often used when talking about the size and variability of people (Anthropometry).
Pinch Grip:
A type of grip that requires an object to be picked up between the thumb
and one or more fingers or the fingers and the palm or the finger tips and
the base of the fingers. A pinch grip does not allow the hand to fully encircle
the object being handled.
Posture:
The general position of the whole body (e.g. standing, sitting, kneeling)
or, more specifically, the position of any body part / joint with respect
to adjacent body parts or the joint's full range of motion.
Power Grip:
A grip allowing the four fingers and thumb to encircle the object. This
grip will generally maximize power on the part of the worker.
Pronation:
The action of rotating the forearm so that the hand is palm down.
Psychophysics:
Deals with the relationship between human sensation and their physical stimuli.
The psychophysical approach used in the study of manual material handling
(MMH) tasks requires the worker to adjust the weight, force or frequency
in a handling situation until they feel it represents the maximum acceptable
weight or force.
Psychosocial Risk Factors:
Various factors can impact a person from both the psychological and social
point-of-view. Some of these factors include work organization, job design,
shift schedule design, work load, feedback, job stress, co-worker relationships,
relationships with supervisors, etc. When one or more of these factors is
seen as negative by a person then the person's health and well-being can
suffer and the rate of accidents, injuries and other work-related disorders
can increase.
[R]
Radial Deviation:
Radial deviation describes a movement of the wrist. Radial deviation occurs
when a person moves / bends the wrist / hand sideways towards the thumb.
When in this posture the person's maximum grip strength is reduced by as
much as 20%.
Radial Nerve:
A large / main nerve that runs from the shoulder, through the arm, ending
in the forearm. This nerve has a number of branches. Two small, superficial
branches of this nerve pass into the hand, outside of the carpal tunnel,
and supply the sensation to some of the skin on the back of the hand and
fingers. This is the nerve you compress when you hit your funny bone!
Range of Motion:
The limits of movement defined at a joint or landmark of the body. Stresses
on the connective tissues at a joint increase as the joint moves towards
the limit of its range of motion.
Rate of Perceived Exertion (RPE):
Rate of Perceived Exertion is a method for subjectively assessing the amount
of effort a worker is exerting. Typically, RPE is measured using a scale
(e.g., the Borg Scale) where the worker ranks their effort from very, very
easy (0/1) to very, very hard (7-10). Some research suggests that for muscular
and aerobic activities the ranking on an RPE scale roughly approximates
the %MVC or percentage of maximum aerobic capacity.
Recovery Time:
Work periods when task demands are light or when rest breaks are scheduled,
permitting a person to recover from heavy effort work such as prolonged
fixed postures.
Repetition:
The number of similar exertions or actions / tasks performed in a specified
amount of time. Repetition may be measures in terms of minutes, hours or
work day (e.g., 3 per minute, 25 per hour, 30 times per shift). See Frequency.
Risk Factor:
Something that increases the likelihood of a negative or unwanted outcome.
For instance, smoking is a risk factor for lung cancer and exposure to jobs
that involve high force exertions with awkward postures is a risk factor
for developing a WMSD. However, the presence of or exposure to any specific
risk factor does not necessarily lead to any one negative or unwanted outcome.
The probability of the negative out come is increased but it is not, usually,
assured. The likelihood of a negative outcome is greatly increased if a
worker is exposed to more than one risk factor at the same time. The 'risk'
associated with any specific risk factor depends on the magnitude, frequency,
and duration of the exposure.
RULA (Rapid Upper Limb Assessment):
A procedure to assess the exposure of people to postures, forces and muscle
activities known to contribute to upper limb disorders. The RULA technique
uses observations of postures adopted by the upper limb, neck, back and
legs. Values are recorded by comparison with assessment charts along with
values for muscle use and loads. The total scores then indicate if any action
is recommended.
[S]
Sprain:
An injury to ligaments where the tough ligament tissue is stretched, partially
or, on occasion, completely torn.
Strain:
An injury to the fibres of a muscle or tendon where the small fibres are
stretched, partially or, on occasion, completely torn.
Static Exertion:
Static exertions refer to physical exertions (gripping, holding a posture)
in which the same position or posture is held throughout the exertion (also
referred to as "static loading").
Stress:
A non-specific physiological and psychological response to situations, events,
persons, environments, etc. Situations that are perceived as either negative
or positive will elicit the same response. However, prolonged exposure to
negative stressors without any ability to resolve the situation may have
a negative affect on a person's health and well-being.
Supination:
The action of rotating the forearm outward so that the hand is palm up.
[T]
Task Analysis:
An systematic approach for documenting and assessing the risks associated
with a specific task or job. Hierarchical Task Analysis (HTA) involves looking
at a job as a series of main or key tasks or objectives and then breaking
these key tasks or objectives down into sub-tasks and sub-task actions.
Tendon:
Strong tissue that connects muscles to bones.
Tendonitis:
Tendon disorder caused by inflammation of the tendon.
Tenosynovitis:
Inflammation of the sheath surrounding the tendon.
Thoracic Outlet Syndrome:
Compression of nerve and blood vessels between arm and neck, causing numbness
and weakness of fingers, hand or arm.
Trigger Finger:
A tendon disorder which occurs when the tendon sheath of a finger swells
so that the tendon becomes locked in the sheath and any attempts to move
the finger will cause a snapping, jerking movement. Trigger Finger usually
strikes the first finger.
[U]
Ulnar Deviation:
Ulnar devation describes a movement of the wrist. Ulnar deviation occurs
when a person moves / bends the wrist / hand sideways towards the little
finger. When in this posture the person's maximum grip strength is reduced
by as much as 25%.
Ulnar Nerve:
A large / main nerve that runs from the shoulder, through the arm and forearm
into the hand. The unlar nerve passes through the wrist to the hand but
it does not run through the carpal tunnel. This nerve supplies the sensation
of temperature, touch and pain to the little finger and one side of the
little finger and thumb and supplies some of the small finger muscles in
the hand.
[V]
Vertebral Disc:
Discs separate the bones (vertebrae) that make up the spinal column. They
are fibrous structures that surround a pulpy, gelatinous centre (nucleus).
They work to help bind the vertebrae together and as the shock absorbers
for the spine. Disc-related injuries to the back can be associated with
deformation of the discs, including bulging and rupturing of the discs.
Vibration:
The oscillatory motion of a physical body. Localized vibration, such as
hand-arm vibration, is produced by contact with powered tools or equipment
or with vibrating structures. Whole-body vibration occurs while standing
or seated in vibrating environments or objects, such as trucks or heavy
machinery.
Vigilance:
Having to pay attention or concentrate for long periods of time. This state
of sustained alertness or vigilance is required in some jobs such as driving
or flying and is especially demanding mentally.
[W]
Whole Body Vibration:
Exposure of the whole body vibration (usually through the feet/buttocks
when riding in a vehicle). Whole body vibration may increase the risk of
low back pain and discomfort.
Working height:
Generally the height at which the hands are positioned. The most favourable
working height while standing is to have a work surface that is 50-100mm
below elbow level. Working heights will vary depending on the stature of
the worker and the nature of the work. Delicate work is generally done higher
than heavier work.
Workplace:
The physical area in which a person performs job activities; includes tables
or counters, chairs, any controls and displays necessary, the lighting and
other environmental factors.
Work Related Musculoskeletal Disorders (WMSDs):
Work-related musculoskeletal disorders (also referred to as Repetitive Strain
Injuries, Cumulative Trauma Disorders, Musculoskeletal Injuries) affect
muscles, tendons, nerves, ligaments, and joints in various parts of the
body. WMSDs are, by definition, work related, and many different work factors
may contribute to their development. The key physical risk factors are force,
posture, repetition and duration. Psychosocial risk factors, such as stress
and workload also play a role.
Workstation:
The entire work area assessed by a worker when performing a specific task
or job cycle.
Workspace envelope:
How far someone can reach from a certain position. The preferred workspace
envelope, where frequently used controls and tools should be placed is the
area a person can reach with the arms hanging down at the sides and the
elbows bent to approximately 90 degrees. The maximal workspace envelope
is the area that can be reached by the full length of the raised arms.
Wrist extension:
The wrist posture where the hand and wrist are bent back / up so that the
back of the hand moves 'toward' the forearm. When in this posture a person's
grip strength can be reduced by as much as 25%.
Wrist flexion:
The wrist posture where the hand and wrist are bent down so that the palm
of the hand moves 'toward' the forearm. When in this posture a person's
grip strength can be reduced by as much as 55%.
This glossary is used with permission from the Association of Canadian Ergonomists/Association canadienne d'ergonomie, http://www.ace-ergocanada.ca
