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Fig. 1 A table was constructed (hal could be adjusted in height between 75 cm and 100 cm above Lhe floor. The angle of lhe table surface could bc varicd from — 10 (o -HO . The adjustmentsare madę by two handlcs which aa on hydraulic pistons attached to the legs of the table

are kept in front of the body the load increases cven morę (Nachemson, 1966; Andersson cral, 1977;SchuItz ztal, 1982). When lhe work is performed at a table thal is too high, a compensatory raising of the shoulders and an abduction of lhe armsare demanded.Such arm positions very ąuickly lead to fatigue in the shoulder muscles even when the load is only the weight of the arm (Hagberg, 1981). The reason why fatigue develops rapidly when the arms are abducted over 30° is thal larger lorque is reąuired and that the shortening of the active muscles decreases thetr capacity lo develop force (ChafTui, 1973). Butchers often work with ihcir neck bent forward. This may cause large load on the neck (Hagberg, 1981). To reduce lhe forward bending of the neck we have suggested Ihat the surface of the tables should be tilted (Magnusson etal, 1981). The use of tilted tables has been adapted in butchcring before, but never thoroughly cvaluaied (Snijders, 1977; Ramel, 1981). By the shorter sight dislance the head could be kept in a morę uprighl and comfortable position. A tilted surface also allows variation of the working height by movement of the workpiece closer to, or further away from, the body. The ergonomie effect of a tilted surface has been studied by Crandjean (1979).

He found that for certain types of office work, an angle of the surface of 60° to 70° reduced the load on the neck and the back. Such a large till is only possible for a few working tasks in which the table must not also function as storage area.

The aim of this study was (I) to investigate the relation between body load and table heights in order to find an optimal height for each butcher, and (2) to investigate the usefulness of a tilted table surface and if possible give recommcndation about the angle.

Materiał and method

A cutting table was constructed which permitted testing both in the laboratory and at workplaces. The table height and the surface angle could be adjusted easily by mcans of handlcs (Fig. 1). Five cxpeiienced butchers participated in che laboratory tesis, which were performed at four different table heights. For the first test each butcher was asked to choose a height that he considered to be the most comfortable. The choice was madę separately while he was cutting up one half of a pig. For the second and the third test, the table was raised and lowered S cm respectively. The last test was performed at the best height in the previous tests, but with the surface tilted 8°. Each table height was measured as well as some body measures of lhe butchers. Here the table height is expressed as the distance between the table surface (at the close edge) and lhe elbow of the butchers. The elbow height was defincd as the distance between lhe floor and the oleeranon when the elbow was flexed 90°.

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Fig. 2 The scheme used for the yideotape analyses. The numbers 1 to 11 represent lhe different tasks when cutting up a

half-pig. The figures betów these denote work moments selected (or evaiuation. The number differs for the different tasks as they vary in time duration and compleaity. At each stop of the tape, observations were madę of the positions of the back. the neck. the shoulders and the arms according to the classesgiven

147

Applied Ergonomie* June 1987