Shoulder load during machine milking. An electromyographic and biomechanical study.

Abstract Ten professional milkers simulated 20 different machine-milking postures related to different vertical distances between milker and cow. The loading moment with respect to the shoulder joint bilateral axes was calculated, and EMGs from four shoulder muscles were recorded. The loading moments were related to isometric strength and EMG was standardized against an isometric maximum contraction. Muscle activity was low to moderate. Load moment increased with increasing level difference between milker and cow, but the simultaneous increase in strength utilization and muscular activation was lower than expected. About 25% of maximum shoulder flexor strength was required. The study illustrates some effects of the interaction between shoulder loading moment, trunk inclination and shoulder flexion. The method used gives load both in absolute form (loading moment) and in relation to individual capacity (strength utilization and normalized EMG).

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