Ergonomics terms explained

Ergonomics Terms Explained
Jayadeva de Silva
10/8/2015 1Jayadeva de Silva

•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.

• Human factors :
H uman 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.)

• 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.

• 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.

• Biomechanics:
The study of the effects of
internal and external forces
on the human body both in
movement and at rest.
• 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.

• 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.
• 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

• 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.

• 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).

• 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

• 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).

• 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.

• 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.

• 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

• 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

• 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

• 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

• 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.

• 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

• 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).
• SeeFrequency also

• 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

• 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.

Jayadeva deSilva
Jayadeva de Silva obtained Master’s degree in Science from Russian Friendship University Moscow and
Diploma in Personnel Management from National Institute of Business Management (SriLanka). He is a fellow
of both the Institute of Personnel Management and Institute of Training & development. He is also
professionally qualified in training systems & curriculum design with an ILO fellowship.A strong advocate of
Human Talents Development, Jayadeva is the principal consultant of humantalents unlimited, a professional
practice that provides training & consultancy in human resources management, development and industrial
relations (IR).
Jayadeva has carried out several HRD & IR consultancy projects and has facilitated numerous management
development programs/strategic planning workshops; He has been trained in many modern management and
leadership concepts. Jayadeva has contributed articles (over 50) and authored the trend setting book ‘Human
Talents Management’.
He founded humantalents International and HRSriLanka virtual learning Groups.Jayadeva de Silva has
functioned as Group Manager (Human Resources Development) of Hayleys Group of Companies a multi-
billion-rupee public listed Group; and Group Director–Human Resources of Brown & Co. a large diversified
company.
He also serves as a resource person for professional and Post graduate courses primarily in the areas of HRM
& HRD at Post graduate Institute, University of Peradeniya, NSBM University.SriLanka Institute of Training and
Development, Oxford College of Business. He is a past president of HRDGateway, an International organization
of over 15,000 HR Professionals worldwide. He is featured in the millennium registry of SriLankan personalities
------------
He can be contacted as follows
E mail djayadeva@gmail.com
Tel 011 2562449
077 7272295
Web https://www.facebook.com/Humantalents
www.slideshare.com/Jayadeva

Ergonomics terms explained

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