An Electromyographic Study of the Middle Deltoid and Middle Trapezius Muscles during Warping

The differences in myoelectric activity of the right middle trapezius and the right middle deltoid were examined for twenty-one 18- to 35-year-old healthy females during two methods of warping yarn. All the women were right-handed and experienced at the task but did not have a preference for either a vertical or horizontal board placement. Baseline EMG data, consisting of unresisted isometric contraction of the shoulder joint at 90° of abduction with the elbow in extension, were collected from the selected muscles prior to the subjects' performance of the task. The baseline activity was used as a means of normalizing the EMG data. Two paired t tests of the normalized EMG activity demonstrated that both muscles were significantly more active when warping was performed in the horizontal position (p <. 001) than in the vertical position, making the horizontal positioning of a warping board better to use when these muscles need to be exercised.