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Work organizational factors broadly consist of job content and organization characteristics, as well as temporal and economic aspects of the work and task. Job content is the array of tasks and procedures that make up an employee's workload. These requirements have a direct effect on the exposure to external loads associated with the use of equipment and tools. Other aspects of job content may include specifications to handle certain objects, operate machinery, or work under potentially adverse environmental conditions. Interventions in job content may reduce or eliminate exposure to physical stresses by directly altering the job requirements. Examples include assigning a worker to different tasks or eliminating a specific operation through automation.

Organizational characteristics describe the management structure of the organization and the level of autonomy an employee has when performing a job. These factors may affect employees' attitudes about their work or influence physical stress exposure. Interpersonal relationships among employees and supervisors may also influence physical stress exposure. For example, physical stresses in a cooperative work environment often are reduced when employees informally assist one other. Temporal aspects include job scheduling such as shift work, number of hours on deadline, job rotation, or the frequency and duration of specific tasks. For example, the continuous performance of a monotonous, repetitive task has been associated with physical and psychological stress.

Finally, the economic and compensation policies of a company can affect physical exposures. For example, overtime and extended work can increase the daily duration of exposure to musculoskeletal stressors. Compensation incentives also may affect intensity, frequency, and duration of work and may discourage rest breaks.

PRINCIPLES OF ERGONOMICS

The application of ergonomic principles forms the basis for much of the intervention literature. Ergonomics is the study of work, including workplace interventions to establish compatibility among the worker, the job, and the work environment. Ergonomics professionals, both researchers and practitioners, reflect the variety of factors that affect safety and productivity in the workplace; the disciplines involved include researchers and practitioners in, for example, medicine, epidemiology, psychology, and industrial engineering and other health-related, technical/ engineering, and behavioral disciplines. The process whereby ergonomics is applied to intervention adheres to the scientific method: available data are gathered and analyzed (e.g., through broad or local surveillance and through analysis of jobs); hypotheses are developed (e.g., specific engineering controls are proposed to address specific factors or condi-



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