Ergonomic Glossary


Active Adjustment :

Device to change the geometry of a chair that must be consciously manipulated by the sitter. A mechanism for seat height adjustment is the most common active adjustment on an office work chair.

Adjustable Back:
Chair backrest that can be actively adjusted. For example, an ergonomic task chair has a backrest with three interrelated adjustments — for height, depth, and angle — which are locked into place until the sitter elects to change them.

Adjustable Lumbar Support:
Device to allow the sitter to actively adjust the size of the lumbar region of the chair’s backrest. An ergonomic executive chair has an air-filled bladder that the sitter can manipulate to increase or decrease the size of the lumbar support. Adjustable lumbar support is also found in automotive seating.

Ankle Tilt:
Tilt mechanism that allows the seat of a chair to move about multiple pivot points. As the sitter reclines, the body first rotates about the ankle, then bout the knee and pelvis– the body’s natural pivot points.

Based on measurements of the human body. Anthropometric data is useful in designing anything–like a chair–which has to interface with people.

Having a human form or attributes. Describes objects that have human characteristics.

Formal examination of the opinions of people who sit in ergonomic chairs at their workplace. These opinions are valuable, as people spend a lot of time in their work chairs and become experts on them. Opinions are gathered on a standard questionnaire, allowing the response to be compared with “use test” results taken earlier, when the chair was in the design process, as well as with user opinions of other chairs.

Awkward posture:
Deviation from the ideal working posture of elbows at the side of the torso, with the wrists neutral. Awkward postures typically include reaching behind, twisting forward or backward bending, pinching, and squatting.



Resembling the forms of living organisms. 

Study which uses the laws of physics and engineering concepts to describe the motions of body parts and the forces acting upon them during normal daily activities.



Cumulative Trauma Disorder.

Carpal Tunnel Syndrome: 
A wrist disorder that may be related to repetitive hand work. One example of a cumulative trauma disorder.

Center Column Tilt:
The most common tilting mechanism use in office chairs. The mechanism allows the seat to rotate about a pivot point located at the top of the column that attaches the base to the seat.

Conventional Tilt: 
Center column tilt. “Conventional” in the sense that the tilting motion is familiar.

Cumulative Trauma Disorders (CTD’s):
Injuries of the muscles, tendons, and nerves resulting from doing the same thing over and over without sufficient rest of variety of motion between repetitions. Carpal Tunnel Syndrome is CTD, as is tendonitis. Repetitive motion injuries is another common term for this group of disorders.



Quality that describes the ability of a chair to maintain a tilting posture between full upright and full recline with little effort on the part of the sitter. 



Engineering controls:
A method of controlling worker exposure to risk factors by redesigning equipment, tools, and work stations. Engineering controls are part o hazard prevention and control.

The scientific study of human work. The term comes from the Greek words “ergos” meaning work, and “nomos,” meaning natural laws of. Ergonomics considers the physical and mental capabilities and limits of the worker as he or she interacts with tools, equipment, work methods, tasks, and the working environment. Ergonomic features should be present in all furniture. Recently, ergonomic features have been emphasized in computer support equipment.

Ergonomics program:
A systematic method (similar to an accident prevention or quality improvement program) used to evaluate, prevent and manage work-related musculoskeletal disorders. The four elements of a typical ergonomics program are worksite analysis, hazard prevention and control, medical management, and training and education.

Ergonomics team:
Those responsible for the identifying and correcting of musculoskeletal hazards in the workplace ergonomics program.



A condition that results when the body cannot provide enough energy for the muscles to perform a task.

The amount of physical effort a person uses to do a task.

Forward-sloping Seat: 
Any seat where the back of the seat pan is higher than the front edge. Some chairs designed to accommodate forward-sitting posture have seats with a pronounced forward slope to promote an open thigh-to-trunk angle.



General Office Chair:
A chair designed to accommodate workers whose jobs include many tasks during   their work day. These chairs should be less restrictive than a chair designed to accommodate a single task. 



Hand-arm vibration: 
Vibration (generally from a hand tool) that goes through the hand, then travels through the rest of the body. 

Hazard prevention and control:
Eliminating or minimizing the hazards identified in the worksite analysis. It is changing the jobs, workstations, tools or environment to fit the worker. Hazard prevention and control is an element of the ergonomics program.



Incidence rate:
The rate at which new injuries and illnesses occur for a given job, production line, work area, department or the company. 

Intervertebral Disc:
Elastic disc — a fibrous outer ring enclosing a pulpy inner nucleus — interposed between adjoining vertebrae of the spine. Deterioration of the intervertebral disc through injury or disease leads to back pain.

“U”- shaped bones within the buttocks that carry most of the weight of the upper body in a seated position.





Knee Tilt:
A tilting mechanism for a chair which causes the body to rotate around a pivot point located near the sitter’s knee.

Knuckle Tilt:
Center column tilt. So called because it is a single pivot mechanism mounted on the end of the column, similar to a knuckle joint in the human finger.

Natural outward curve of the upper spine. Unnatural outward curve of the lower spine that occurs when the angle between the thigh and torso in a seated position is less than 90 degrees. 



Natural inward curve of the lower spine.

Lumbar Region:
Area of the lower spine commonly referred to as the lower back. Technically , the lumbar vertebrae are the five spinal segments just above the sacrum or tailbone.

Lumbar Support:
Part of a chair backrest that supports the muscles of the lumbar region when sitting    upright and promotes lordosis of the lumbar spine when reclining.



Material Intelligence:
Term used to describe materials whose properties change for the benefit of the user during use. Eyeglasses with lenses that darken in sunlight possess this “intelligence”, as does the shell of the Equa chair, which flexes to increase lumbar support as the user reclines.

Mechanical contact stress:
The contact of the body with a hard surface or edge that results in the compression of tissue. Can also result when using a part of the body as a hammer or striking instrument.

Medical management:
The effective use of available health-care resources to prevent or manage work-related musculoskeletal disorders. Medical management is an element of the ergonomics program.

Muscle Tonus:
A state of partial contraction characteristic of normal muscle. Loss tonus occurs when there is insufficient stimulation of the muscle for prolonged periods of time, as when maintaining a single seated posture.

Musculoskeletal disorders:
Illnesses and injuries that affect one or more parts of the musculoskeletal system.

Musculoskeletal system:
The soft tissue and bones in the body. The parts of the musculoskeletal system are bones, muscles, tendons, ligaments, cartilage, nerves, and blood vessels. 



Neutral posture:
Comfortable working posture that reduces the risk of musculoskeletal disorders. The joints are naturally aligned with elbows at the side of the body and wrists   straight.





Passive Adjustment:
Device that changes the geometry of a chair that is unconsciously manipulated by the sitter.  For example, reclining in a chair passively adjusts the seat angle. An example of a more sophisticated passive adjustment is the way lumbar support automatically increases as the sitter reclines. The advantage of passive adjustment is that they allow unselfconscious sitting,” providing the support the sitter needs without requiring the conscious effort of a manual or active adjustment.

Personal protective equipment(PPE):
Gloves, kneepads and other equipment that may help reduce hazards until other controls can be implemented, or to supplement existing controls.

Pivot Point:
Literally, a shaft or pin on which something revolves. A pivot point can also be imaginary; a football pivots about an invisible line drawn from nose to nose as it is thrown through the air.

Popliteal Height: 
Distance from the floor to the crease right behind the knee. One of the anthropometric measurements used for determining seat height.

Postural Stasis:
Condition where a single body position is held for long periods of time. The health risks of postural stasis include restricted blood circulation, fewer nutrients to the intervertebral discs, and atrophy of muscle tissue.

Posterior Alignment:
Semi-reclined posture often preferred by VDT workers, similar to that assumed by automobile drivers. Thighs are horizontal and the back is reclined about 10 degrees from vertical.





Work chair that use a backward tilt rather than a forward sloping seat to promote an open thigh-to trunk angle.

Records review:
Reviewing company records to identify patterns of injuries (or potential injuries) to help you find the jobs and workstations that may contain musculoskeletal hazards.

Performing the same motions repeatedly. The severity of risk depends on the frequency of repetition, speed of the movement or action, the number of muscle groups involved, and the required force.

Risk factors: 
An aspect of a job that increases the worker’s chance of getting a work-related musculoskeletal disorder.



Severity rate:
The cost in terms of lost workdays (or dollars) of new injuries and illnesses occurring in a given job, production line, work area, department or company.

Forces that act in opposite directions, such as the sliding that occurs when a body and its clothing come into contact with the surface of a chair. Shear forces are minimal, which allows the sitter to recline without untucking a blouse or shirt. Shear forces are high in a forward-sloping chair when clothing tends to stay with the seat while the body slides forward.

Spinal Disc: 
See intervertebral disc. 

Static loading:
Physical effort or posture that is held and requires muscle contraction for more than a short time. As muscles remain contracted, the blood flow to the muscles is reduced. (Also sustained exertions.)

Sustained exertions:
Physical effort or posture that is held and requires muscle contraction for more than a short time. As muscles remain contracted, the blood flow to the muscles is reduced. Also static loading.) 



Task Chair:
A chair designed for people whose jobs consist of one main task: looking into a microscope, talking on the phone, using a video display terminal.

Thigh-to-Trunk Angle:
Angle between imaginary lines drawn from the knee and the neck, intersecting at the hip. In a standing position, a person’s thigh-to-trunk angle is close to 180 degrees. In a seated position, a thigh-to-trunk angle greater than 90 degrees helps maintain the natural curve of the spine.

Formation or presence of a blood clot within a blood vessel.

Tilt Lock:
Device that freezes the tilting action of the seat pan. On some chairs, tilt lock can be used to lock the chair in any position between upright and full recline. In others, it simply locks the chair in its most forward position.



Unselfconscious Sitting: 

Ability to sit and move in a chair without thinking about the chair or its adjustments. Passive adjustments allow for unselfconscious sitting.

Use Test:
Formal examination of the opinions of people who are asked to use experimental chairs.





Work Chair:
General office chairs and task chairs. The chair that the main occupant of a work station would use most of the time.

Work practice controls:
Procedures for safe and proper work that are used to reduce the duration, frequency or severity of exposure to a hazard. They include work methods training, job rotation, and gradual introduction to work. Work practice controls are part of hazard prevention and control. 

Worksite analysis:
A safety and health review that addresses work-related musculoskeletal disorders. It is a structured way of identifying jobs and workstations that may contain musculoskeletal hazards, the risk factors that pose the hazards, and the causes of the risk factors. Worksite analysis is an element of the ergonomics program.