Purpose: In this study, we investigated the effects of combining the resistance of an elastic band with slow abdominal breathing on shoulder periarticular muscle activity during shoulder adduction-abduction. Methods: Subjects were eight healthy adult males. Abduction of the shoulder was performed from 0° to 90° (with adduction being defined as the movement from 90°to 0°) for a period of 8 s. The three conditions under which abduction-adduction were performed comprised the following: without an elastic band; with an elastic band; and with an elastic band during slow abdominal breathing. The activities of the biceps brachii, deltoid (anterior, middle, and posterior fibers), trapezius (upper, middle, and lower fibers), and the pectoralis major muscles were measured. Results: Muscle activity of the shoulder periarticular muscles was increased when the elastic band was used. When this was combined with slow abdominal breathing, muscle activity significantly increased in the middle fibers of the deltoid muscle and in the trapezius muscle during abduction while exhaling. Muscle activity significantly decreased in the biceps brachii muscle and the anterior fibers of the deltoid muscle during adduction while inhaling. Discussion: During shoulder abduction, fixation of the trunk occurred initially before the onset of abduction. At this point, exhalation resulted in contraction of the transversus abdominis muscle, a muscle that stabilizes the trunk, thereby enhancing trunk stability and raising the efficiency of deltoid muscle contraction. Conclusion: The results suggested that shoulder abduction performed in combination with slow abdominal breathing increased the efficiency of deltoid and trapezius muscle activities.