یک راه حل برای مشکلات ارگونومیک یک میز جدید برای کار با یک میکروسکوپ
|کد مقاله||سال انتشار||تعداد صفحات مقاله انگلیسی||ترجمه فارسی|
|7222||2003||8 صفحه PDF||سفارش دهید|
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Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Applied Ergonomics, Volume 34, Issue 6, November 2003, Pages 621–628
Microscope workers are exposed to continuous static muscular work and an increased risk of musculoskeletal disorders in the neck, shoulder and upper extremities. In a Finnish research centre, microscope workers reported pain in the shoulder, neck, lower back and upper back. As a consequence, a programme to solve the ergonomic problems of microscope work was initiated and led to the construction of a new table for microscopes. Ten experienced male microscope workers were chosen as subjects to carry out an experimental study in which the new table and an old one, an ordinary non-adjustable laboratory table, were compared in a standardized microscope task. The dependent variable was the electromyographic activity measured from muscles in the neck–shoulder region. The new table allowed the microscope to be used with the head in an upright position, the forearms supported and with less flexion of the upper arm. Surface electromyographic measurements also confirmed that the changes were ergonomic improvements.
Microscope workers are exposed to continuous static muscular work and an increased risk for musculoskeletal disorders in the neck, shoulder and upper extremities, and ergonomic guidelines and solutions are needed to help prevent such risks among these workers (Haines and McAtamney, 1993; Kalavar and Hunting, 1996; Krueger et al., 1986). The Geological Survey of Finland is a modern research centre where over 100 persons work with a microscope for 10–50% of their total work time. According to a questionnaire survey, the microscope workers in this centre suffer from pain in the shoulder region (75%), the neck region (57%), the lower back (49%) and the upper back (39%). The most detrimental symptoms were found to be the sensation of neck stiffness, neck pain and difficulty to turn the head sideways. A programme to solve the ergonomic problems of microscope work was carried out in 1995-96. Different types of work with a microscope were studied, the working postures and movements were analysed, and the workers were asked for suggestions for improving the microscope table. The programme resulted in the following instructions for the safe use of microscopes: Characteristics for an ergonomic microscope: • Adjustable ocular angle. • Adjustable ocular height. • Adjustment knobs (focusing, nicols, revolving stage) sufficiently low. • Possibility to attach a forehead support (a forehead support was tested, and its use decreased muscular activity in the neck). Characteristics for an ergonomic chair: • Stable, if on castors, then castors should be lockable. • Seat height easily adjustable (small women–tall men). • Adjustable angle and depth of the seat. • High back support, adjustable in height and angle (support of low back). • Neck support, adjustable in height and in frontal plane. • Optional armrests, adjustable in height, sideways and in frontal plane. Characteristics for an ergonomic microscope table: • Stable. • Adjustable in height (crank, electrical, etc.). • Sufficient amount of space (manual, counter etc.). • Sufficient amount of leg room. • Cut-away section at the front of the table (sitting near the microscope, arm support). • Tiltable microscope level (ocular angle). • Support for the forearms and the forehead. • Adjustable forearm support with soft padding. • Adjustable forehead support attached to the microscope or the table. The microscope workers in the Geological Survey of Finland had an ergonomic, fully adjustable chair, they used conventional (non-adjustable ocular height and angle), high standard, expensive microscopes and ordinary laboratory tables. The management found it too expensive to replace the expensive, well-working microscopes with new, ergonomic ones. Therefore to improve the ergonomics of microscope work in the research centre, they chose to have a new microscope table designed. For good working posture and minimal complaints, a microscope workstation should be adjustable to fit different size operators. Operators should be able to reach all the controls with their elbows resting on the table (Kreczy et al., 1999; Nielsen, 2000; Helander et al., 1991). Along with these guidelines, we used the knowledge gathered in the ergonomic programme carried out in the Geological Survey of Finland to construct a new table for microscope work (Sillanpää and Viljanen, 1996). The new table had a height adjustable and tiltable middle section, on which the microscope was placed, along with adjustable right and left sections. Finally, a section at the front of the table was cut-away so that the operators could place their forearms on the table. The new table allowed the microscope to be used with the head in an upright position and the forearms supported and with less flexion of the upper arm. The objective of this study was to compare the effects of working with the new microscope table on muscular load in the neck–shoulder region during a standardized microscope task with the effects of working on an ordinary non-adjustable laboratory table.
نتیجه گیری انگلیسی
We compared the effects of working with an old and a new more ergonomic table on muscular load in the neck-shoulder region during the use of a microscope. The results showed that changing the table reduced muscular activity. We used EMG to evaluate the differences in working postures and muscle activity, and abandoned the use of postural analysis as a measure of the change because of the very small visible changes in posture and the kyphotic changes in postures of some subjects. It has been common to normalize the EMG amplitudes against the MEMG to deal with inter-individual variation. After this procedure, the activities can be expressed as the percentage of the maximum EMG amplitude measured during the MVC test. In agreement with Yang and Winter (1984) and our earlier studies (Sillanpää et al., 2000; Sillanpää et al., in press), we found that normalization to the individual mean of each subject was more effective in reducing the inter-individual variation than normalization to the MEMG was when the variation coefficient was used. However, it is still difficult to interpret the practical meaning of the statistically significant differences. To make such an interpretation possible, we used the corresponding mean percentages of the MEMG. We found that the new table allowed the microscope oculars to be used at the correct height, as determined by the more upright position of the head and the reduced muscle activity in the neck. The reduction of muscle activity in the neck was both statistically significant and meaningful according to the limits of Jonsson. It was especially meaningful that the static load in the neck was reduced because workers had reported that neck stiffness, neck pain and difficulty in turning the head sideways were the most detrimental symptoms. The subjects had worked on a microscope 17 years on average and some of them had tense breast muscles that resulted in a kyphotic upper back, which could be seen in the form of unsatisfying neck and upper back postures even on the new table (Fig. 1). The new table had a tiltable microscope level. Tilting the microscope makes it possible to reduce the ocular angle of the microscope and, to some extent improve the neck position. The section cut out of the table allowed the user to sit near the microscope and therefore the flexion in the upper arm was reduced, as was the EMG activity in the left deltoideus anterior muscle. The adjustable side sections provided support for the forearms and led to a tendency towards a reduction in the EMG activity of the trapezius and left deltoideus medialis muscles. The activities in the trapezius muscles were still noteworthy, but that in the deltoideus muscles was very low with respect to Jonsson's limits. The sharp edges of the middle section of the table top, on which the microscope was placed, and the lack of padding on the surface of the side sections may have prevented full support of the arms and may have even increased unnecessarily the abduction of the upper extremities and, therefore, also the muscle activity in the right deltoideus medialis muscle. The results indicate that the use of the new microscope table may help relieve typical musculoskeletal disorders of microscope workers (Buckle, 1997; Kreczy et al., 1999; Nielsen, 2000; Helander et al., 1991). Ten experienced male microscope users were chosen as subjects because the workers who carry out the main task, identifying minerals from a rock slice, are mainly men in the research centre. The results of the test are as relevant for women as for men because the range of adjustments have been designed for users-from small women (P 0.05) to tall men (P 0.95)-and they were easy to make. The subjects reported that work at the new table was lighter or much lighter than at the old table, and they found working at the new table easier. A major benefit proved to be the more relaxed position of the neck. The research centre has continued to develop the microscope table. The most recent prototype is illustrated in Fig. 3 and Fig. 4. The table is equipped with an electrically adjustable microscope level, and the side sections and the height are adjustable for both sitting and standing positions. The effects of microscope work on the occurrence of musculoskeletal disorders should be taken seriously. Our study shows that the ergonomic conditions of microscope work can be improved in relation to muscle load in the neck-shoulder region and upper extremities. In addition to the indicated ergonomic solutions, workstation design organizational aspects should be considered (i.e. work-rest schedule, task rotation, counter-motion etc.).