Lean Workstations: Glossary of Ergonomics Terms
Accommodation: any modification or adjustment to a work environment that enables an operator to perform essential job functions.
Administrative controls: procedures and methods, set up by the employer, that significantly reduce exposure to risk factors by altering the way in which work is performed. Examples include job rotation and adjustment of work pace.
Anthropometry: the science of studying human body dimensions. It is used to design ergonomic standards, assembly procedures and workstations. The goal of anthropometry is to minimize design incompatibility and maximize human performance.
Awkward posture: deviation from the ideal working posture of elbows at the side of the torso, with the wrists neutral. It is associated with an increased risk for injury. Awkward postures typically include reaching behind, twisting, forward or backward bending, pinching and squatting.
Biomechanics: a field of study that 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.
Boundary values: a guideline used to design for the 5th to 95th percentile, which means designing for about 90 percent of a given population. The range of sizes dictates the range of flexibility necessary for new workstations, material handling equipment or assembly tools in order to accommodate the full range of employees. Usually, boundary values are obtained from large existing databases.
Carpal tunnel syndrome: a wrist disorder often associated with repetitive hand work. Symptoms include burning, itching, prickling or tingling feelings in the wrist or first three fingers and thumb. Carpal tunnel syndrome is more prevalent in women than in men. It is one example of a cumulative trauma disorder.
Chronobiology: the science of investigating and objectively quantifying phenomena and mechanisms of the biologic time structure, such as circadian rhythms. It is a new and rapidly developing specialty.
Cumulative trauma disorder (CTD): premature wear and tear damage to specific body structures. CTD injuries are mostly caused by low intensity forces applied over a long period of time, with motions repeated over and over concentrated on specific muscles and joints. Common examples of CTD include carpal tunnel syndrome and tendinitis. Cumulative trauma disorder is also called "repetitive motion injury."
DeQuervain's disease: an inflammation of the tendon sheath of the thumb attributed to excessive friction between two thumb tendons and their common sheath. It is usually caused by twisting and forceful gripping motions with the hands. The disorder is named after a French doctor who first described it.
Duration: the length of exposure to a risk factor. It can be measured as the minutes or hours per day that an operator is exposed to a risk. Typically, the greater the duration of exposure to a risk factor, the greater the degree of risk.
Engineering controls: physical changes to a job that reduce musculoskeletal disorders. Examples of engineering controls include changing or redesigning workstations, tools, equipment or processes.
Ergonomics: the scientific study of human work. It is derived from the Greek words ergon (work) and nomos (laws). 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.
Ergonomist: an individual who analyzes work environments and recommends administrative, engineering and work practice controls. Ergonomists attempt to remove barriers to quality, productivity and safe human performance by fitting products, tasks and environments to people.
Exposure: a concept used to describe the particular risk factor experienced by a worker, with a profile of modifying factors, such as intensity, time characteristics and duration.
Fatigue: a condition that results when the human body cannot provide enough energy for the muscles to perform a task. There is a reduction in the ability to exert force in response to voluntary effort.
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 at the shoulder, neck, forearm, wrist, hand and lower back.
Frequency: the number of cycles occurring per time unit.
Global boundaries: the working population used to generate boundary values. If global boundaries are not considered, data can easily be misrepresented. For instance, a 95th percentile male at an auto parts assembly plant in Michigan will be different in height and arm length from individuals working at similar plants in China and Mexico.
Human factors: a branch of ergonomics that focuses on cognitive performance of humans.
Job rotation: a practice in which operators are rotated through several different assembly tasks during a shift. While two or more tasks may require repetitive motion, a different group of muscles or tendons will be worked. Job rotation is a common type of work practice control. But, it is often misused--workers get rotated into similar jobs, and so rotation has no effect.
Kinesiology: a field of study that focuses on the principles of mechanics and anatomy in relation to human movement.
Motion economy: a set of basic principles codified by Ralph Barnes in the 1930s. The principles of motion economy make repetitive tasks easier, more efficient and more effective.
Musculoskeletal disorder (MSD): an injury or illness of soft tissues of the upper extremity (fingers through upper arm), shoulders and neck, low back and lower extremity (hips through toes). It is primarily caused or exacerbated by workplace risk factors, such as sustained and 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. Injuries arising from slips, trips, falls and similar accidents are not considered to be a MSD.
Neutral posture: a 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. The more a joint deviates from neutral posture, the greater the risk of injury.
95th percentile: a term commonly used to determine ergonomic boundary values. It means that the dimensions of an individual are greater than 95 percent of the male population, and 100 percent of the female population, since women are smaller than men as a population. At the 95th percentile, five out of every 100 individuals exceed the target value. Special accommodations may be required for these particularly short or tall individuals.
Optimal work zone: an area in front of the body defined by keeping the back straight, the shoulders neutral and the hands between hand rest and elbow height.
Personal protective equipment (PPE): special devices that operators wear to provide a protective barrier between the employee and a MSD hazard. Examples include vibration-reduction gloves, wrist braces and back support belts.
Raynaud's syndrome: a medical condition where blood vessels of the hand are damaged from repeated exposure to vibration over a long period of time. The skin and muscles do not get the necessary oxygen from the blood and eventually die. Symptoms include intermittent numbness and tingling in the fingers; pale, ashen and cold skin; and eventual loss of sensation and control in the hands and fingers. Raynaud's syndrome is also called "white finger."
Reaction torque: the force created when a threaded fastener forms a solid joint during the run-down phase.
Recovery time: the length of rest between exertions. Inadequate rest periods between exertions can decrease performance. As the duration of the uninterrupted work increases, so does the amount of recovery time needed. Short work pauses can reduce discomfort.
Repetition: the number of similar exertions performed during a task. Repetition is only one risk factor and must be evaluated in terms of other factors such as force, posture, cold and vibration.
Repetitive motion injury: see "cumulative trauma disorder."
Repetitiveness: 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 an operator's chance of getting a work-related musculoskeletal disorder. There are several basic risk factors, including force, posture, repetition and vibration.
Segmental vibration: vibration applied to the hands and arms through a tool or piece of equipment. This can cause a reduction in blood flow to the hands and fingers. It can also interfere with sensory receptor feedback, leading to increased handgrip force to hold the tool. A strong association has been reported between carpal tunnel syndrome and segmental vibration.
Strain: an injury to a muscle or tendon.
Tendinitis: a painful inflammation or swelling that occurs when a muscle or tendon is repeatedly tensed from overuse or unaccustomed use. The elbow, shoulder and wrist are common locations for this injury. Tendinitis is one example of a cumulative trauma disorder.
Threshold limit value (TLV): an occupational exposure value to which nearly all workers can be exposed day after day for a working lifetime without ill effect.
Trigger finger: a tendon disorder that occurs when there is a groove in the flexing tendon of the finger. If the tendon becomes locked in the sheath, attempts to move the finger cause snapping and jerking movements. Trigger finger is usually associated with tools that have handles with hard or sharp edges.
Vibration: oscillation or periodic motion of a rigid or elastic body from equilibrium. Electric and pneumatic tools, such as screwdrivers, generate vibration that can cause injury over time.
White finger: see "Raynaud's syndrome."
Work practice controls: procedures for safe 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.
Working reach envelope: the space about a person created by the reach capabilities to grasp an object with the back straight and minimal deviation of the elbow and shoulder from a neutral position.