Assistive devices provide mechanical advantages when dealing with loads. An example would be a lifting device such as a lift table, a hoist or a patient lifter. Tool redesign could be thought of as a sub-set of machinery design, but we have separated them due to the extensive efforts in tool redesign. Examples would be a reduction in the weight of powered hand tools, improved grip designs, alternative keyboard designs, and alternative mouse designs. The primary risk factors addressed with engineering redesign are loads (forces, weights) and body part postures.

Work methods improvement is also aimed primarily at biomechanical risk factor control, but can also influence the psychosocial work environment. The improvement requires changes in employee behavior to achieve risk reduction. This approach is often accompanied by employee training to provide a basis for the behavior change. The main direction of work methods improvement is to modify the task design to reduce or eliminate risk factors. An example would be changing the techniques used in cutting meat to reduce the frequency of cutting motions, and to improve body part postures while reducing loads.

Administrative controls are aimed at reducing the time of exposure to biomechanical and psychosocial risk factors. The two main directions are rotating employees among jobs with differing exposures and the use of rest breaks. Improved medical management activities could also be considered as administrative controls although the OSHA Ergonomic Guidelines for the Red Meat Industry considers medical management as a separate category.

Training is aimed at informing employees about the risk factors of musculoskeletal injury, and/or changing behavior to reduce risk. An example would be an ergonomic education program that provides employee orientation to risk factors. Another would be providing on-the-job instruction in revised task methods. A third would be providing instruction on how to use specific capabilities of workstation adjustments such as how to properly adjust a chair or a work table.

Exercise and work hardening programs increase the capacity of the employee. That could mean increasing strength, or flexibility, or tolerance for pain, or skills to conduct tasks.

Personal protective equipment typically blocks employee contact with a hazard. For musculoskeletal injury, an example would be gloves to dissipate the energy from hand tool vibration. However, for musculoskeletal injury there is another type of personal protective device that serves as a "support" for the musculature to reduce/balance forces: the back belt (or similar devices).

C. Methods Used to Review the Literature

The methodology used to evaluate the state of intervention research for the control of musculoskeletal disorders proceeded in five phases as outlined in Table 1.

Phase 1 consisted of a comprehensive search to find any article related to musculoskeletal disorder interventions. To accomplish this, the on-line databases PsychLit (1974—present), Engineering Index (1987—present), and Medline (1966—present) were searched using 21 different search terms related to musculoskeletal disorder interventions, put into various combinations. At the same time, we looked through 14 different publications which included NIOSH publications, text and reference books in Ergonomics, and National Safety Council publications. The combined efforts yielded 720 articles.

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