Ergonomics terms explained

05/03/2023 Jayadeva de Silva 1

Ergonomics Terms Explained

Jayadeva 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.

http://www.ace-ergocanada.ca/index.php?contentid=245


• 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


• 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


• 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 de Silva

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 [email protected] Tel 011 2562449 077 7272295 Web https://www.facebook.com/Humantalents www.slideshare.com/Jayadeva

mailto:[email protected]

https://www.facebook.com/Humantalents

http://www.slideshare.com/Jayadeva

Ergonomics terms explained

Education

Transcript of Ergonomics terms explained