Design of Work-Rest Schedules for VDT Operators.

Abstract

The number of musculoskeletal and psychological discomforts is increasing as a result of continuing growth of VDT work. Although ergonomic improvements in workstation design can be applied, an effective work-rest schedule is an economical way to reduce these problems. The objective of this research was to determine an effective work-rest schedule for VDT operators. In addition to a discomfort questionnaire, performance and electromyography measurements from trapezius and flexor carpi radialis were used. Three different work-rest schedules were applied: 60-minute work/10-minute rest, 30-minute work/5-minute rest, and for the third schedule, the subjects received four breaks from VDT work each hour additional to a 14-minute break after two hours. Three of these breaks were 30 seconds in length and the fourth break was 3 minutes in length. The research also considered the effect of type of VDT task. Subjects were asked to enter alphanumeric data for data entry task and to solve addition/subtraction problems as mental task. The results indicated that effect of schedule was different on discomfort levels and performance of the subjects. Similarly, the type of task had different effects on discomfort, performance, and muscular tension levels. The 15/micro schedule was superior to the other schedules in terms of discomfort levels of the neck, back, and elbow/arm, eyestrain, speed, accuracy, and performance for both tasks. The lowest levels of trapezius muscle tension for data entry and flexor carpi radialis for mental tasks were resulted in the 15/micro schedule. The effect of the type of task was significantly different with 60/10 schedule on discomfort in shoulder and chest, bluffed vision, and headache; with 30/5 schedule on shoulder, chest and elbow/arm discomforts; and with 15/micro on discomforts in shoulder and hand/wrist. The schedule effect was different on data entry task for neck, lower back, elbow/arm discomforts and on mental task for headache. Mental task resulted in a higher psychological discomfort, lower physical discomfort, and lower performance than data entry task. The results of the study suggest that the 15/micro schedule is superior to the longer and infrequent rest break schedules considering upper extremity discomfort, eyestrain, speed, accuracy, and performance of the subjects.