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In human anatomy, the deltoid muscle is the muscle forming the rounded contour of the shoulder. Anatomically, it appears to be made up of three distinct sets of fibers though electromyography suggests that it consists of at least seven groups that can be independently coordinated by the central nervous system.〔 Brown JM, Wickham JB, McAndrew DJ, Huang XF. (2007). Muscles within muscles: Coordination of 19 muscle segments within three shoulder muscles during isometric motor tasks. J Electromyogr Kinesiol. 17(1):57-73. PMID 16458022 〕 It was previously called the deltoideus (plural deltoidei) and the name is still used by some anatomists. It is called so because it is in the shape of the Greek capital letter delta (Δ). It is also known as the common shoulder muscle, particularly in other animals such as the domestic cat. Deltoid is also further shortened in slang as "delt". A study of 30 shoulders revealed an average mass of (range –) in humans.〔Potau JM, Bardina X, Ciurana N, Camprubí D. Pastor JF, de Paz F. Barbosa M. (2009). Quantitative Analysis of the Deltoid and Rotator Cuff Muscles in Humans and Great Apes. Int J Primatol 30:697–708. 〕 ==Structure== The deltoid originates in three distinct sets of fibers, often referred to as "heads":〔(The Anatomy of the Shoulder Muscles ): "The Deltoid is a three-headed muscle that caps the shoulder. The three heads of the Deltoid are the Anterior, Lateral, and Posterior."〕 * The anterior or clavicular fibers arises from most of the anterior border and upper surface of the lateral third of the clavicle. The anterior origin lies adjacent to the lateral fibers of the pectoralis major muscle as do the end tendons of both muscles. These muscle fibers are closely related and only a small chiasmatic space, through which the cephalic vein passes, prevents the two muscles from forming a continuous muscle mass. * *The anterior deltoid〔(Anterior Deltoid )〕 are commonly called front delts〔(Pick up your delts ) from Muscle and Fitness: "target point: front/middle delts"〕 for short. * Lateral or acromial fibers arise from the superior surface of the acromion process of the scapula.〔 * *They are commonly called lateral deltoid.〔(Lateral deltoid )〕 This muscle is also called middle delts,〔 outer delts,〔(The Best Exercise for Outer Delts ) on LiveStrong.com in 2011〕 or side delts〔 for short. * *They are also mistakenly called medial deltoid,〔(Shoulders Anatomy ) by Yu Yevon〕 which is wrong, as their origin is the least medial portion of the deltoid. * Posterior or spinal fibers arise from the lower lip of the posterior border of the spine of the scapula.〔 * *They are commonly called posterior deltoid〔(Posterior Deltoid )〕 or rear deltoid〔(Rear Deltoid Stretch )〕 (rear delts for short〔(Lee Hayward - Rear delts )〕 ). Fick divided these three groups of fibers, often referred to as parts (Latin: ''pars'') or bands, into seven functional components: the anterior part has two components (I and II); the lateral one (III); and the posterior four (IV, V, VI, and VII) components. In standard anatomical position (with the upper limb hanging alongside the body), the central components (II, III, and IV) lie lateral to the axis of abduction and therefore contribute to abduction from the start of the movement while the other components (I, V, VI, and VII) then act as adductors. During abduction most of these latter components (except VI and VII which always act as adductors) are displaced laterally and progressively start to abduct.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Deltoid muscle」の詳細全文を読む スポンサード リンク
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