[Purpose] The purpose of this study was to investigate the muscle activity patterns during shoulder movement by non-negative matrix factorization. [Methods] Eighteen healthy young adults were the subjects of this study. Muscle activities of the anterior, middle, and posterior deltoid, infraspinatus, upper, middle, and lower trapezius, latissimus dorsi, serratus anterior, and pectoralis major muscles were measured with a surface electromyograph during shoulder elevating and lowering movement, and muscle activity patterns were classified into 3 synergies using non-negative matrix factorization. [Results] Muscle activity patterns were classified: Synergy 1, in which activity increases with the elevation angle; Synergy 2, in which activity increases in the first and second halves of the movement; and Synergy 3, in which activity increases in the first half of the movement. Deltoid showed significantly higher in Synergy 1. Infraspinatus showed significantly higher in Synergy 2 and Synergy 3 compared to Synergy 1. Synergy 2 was significantly higher in the upper and middle trapezius, and Synergy 3 was significantly higher in the serratus anterior. [Conclusion] The activity patterns shown by the nonnegative matrix factorization were consistent with the theoretical roles, and it might be applied as a new analytical method.
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