In order to clarify if light manual precision work influences the activity of shoulder muscles, seven shoulder muscles were examined using electromyography (EMG) in five different arm positions in ten subjects. The subjects were asked to perform light precision work with the hand while maintaining the same arm position. The EMG activity in the shoulder muscles with the arm in specific positions was compared to the activity when manual precision work was added. The results were analysed statistically using a non-parametric method. We found an increased EMG activity in almost all arm positions and muscles. The increase was significant in four out of five arm positions regarding the infraspinatus and in three out of five positions concerning the levator scapulae. In the supraspinatus the increase was significant with the arm in its highest location. The average increase in shoulder muscle activity amounted to 22% of the resting activity.