Electromyographic analysis of a postal sorting task

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Abstract
In the Dutch postal system, letters are sorted by means of a sorting frame, consisting of a two-dimensional array of pigeon-holes. By means of electromyography, the load on three shoulder muscles (trapezius, and anterior and lateral parts of the deltoid muscles) was measured as a function of location of pigeon-holes. The vertical position of the pigeon-hole appeared to be the most significant factor for the load on the three muscles. The eccentricity along a horizontal axis also contributed; this is interpreted as indicating the distance to the shoulder joint. The top row of pigeon-holes required much more muscular activity than the other pigeon-holes. The relevance of these findings to the occurrence of occupational arm-shoulder syndromes is discussed, and consequences for the redesign of the sorting frame are indicated.