Screening jobs for physical and psychological risk factors is very proactive, and should involve one or more of the following:
A great deal of research has been conducted to identify workplace factors that contribute to the development of musculoskeletal disorders. NIOSH has recently summarized the epidemiological studies that show a relationship between specific work activities and the development of musculoskeletal disorders.
According to the scientific literature, the following are recognized as important risk factors for musculoskeletal disorders, especially when occurring at high levels and in combination. Physical risk factors include:
Body postures determine which joints and muscles are used in an activity and the amount of force or stresses that are generated or tolerated. For example, more stress is placed on the spinal discs when lifting, lowering, or handling objects with the back bent or twisted, compared with when the back is straight. Manipulative or other tasks requiring repeated or sustained bending or twisting of the wrists, knees, hips, or shoulders also impose increased stresses on these joints. Activities requiring frequent or prolonged work over shoulder height can be particularly stressful.
Forceful exertions (including lifting, pushing, and pulling)
Tasks that require forceful exertions place higher loads on the muscles, tendons, ligaments, and joints. Increasing force means increasing body demands such as greater muscle exertion along with other physiological changes necessary to sustain an increased effort. Prolonged or recurrent experiences of this type can give rise to not only feelings of fatigue but may also lead to musculoskeletal problems when there is inadequate time for rest or recovery. Force requirements may increase with:
If motions are repeated frequently (e.g., every few seconds) and for prolonged periods such as an 8-hour shift, fatigue and muscle-tendon strain can accumulate. Tendons and muscles can often recover from the effects of stretching or forceful exertions if sufficient time is allotted between exertions. Effects of repetitive motions from performing the same work activities are increased when awkward postures and forceful exertions are involved. Repetitive actions as a risk factor can also depend on the body area and specific act being performed.
Duration refers to the amount of time a person is continually exposed to a risk factor. Job tasks that require use of the same muscles or motions for long durations increase the likelihood of both localized and general fatigue. In general, the longer the period of continuous work (e.g., tasks requiring sustained muscle contraction), the longer the recovery or rest time required.
Frequency refers to how many times a person repeats a given exertion within a given period of time. Of course, the more often the exertion is repeated, the greater the speed of movement of the body part being exerted. Also, recovery time decreases the more frequently an exertion is completed. And, as with duration, this increases the likelihood of both localized and general fatigue.
Repeated or continuous Contact with hard or sharp objects such as non-rounded desk edges or unpadded, narrow tool handles may create pressure over one area of the body (e.g., the forearm or sides of the fingers) that can inhibit nerve function and blood flow.
Exposure to local vibration occurs when a specific part of the body comes in Contact with a vibrating object, such as a power handtool. Exposure to whole-body vibration can occur while standing or sitting in vibrating environments or objects, such as when operating heavy-duty vehicles or large machinery.
Workplace conditions that can influence the presence and magnitude of the risk factors for MSDs can include:
In addition to the above conditions, other aspects of work may not only contribute to physical stress but psychological stress as well. As long as we believe we have adequate control over all aspects of our job, we may experience normal stress. However, if we believe we have little control over job demands, we may suffer from distress with accompanying ill health and possible irrational behaviors. Under distress, the probability of an accident increases greatly.
Research is examining work factors such as performance monitoring, incentive pay systems, and unreasonable management production demands to determine whether these factors have a negative effect on the musculoskeletal system. Another related area of research is to determine which personal, work, or societal factors contribute to acute musculoskeletal disorders developing into chronic or disabling problems.
The checklist is a formal and orderly procedure for screening jobs. Numerous versions of checklists exist in ergonomics manuals. When checklist data are gathered by persons familiar with the job, task, or processes involved, the quality of the data is generally better. This checklist illustrates three processes:
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