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Anatomy

Wrist Extensors: Functional Anatomy Guide

The wrist extensors are a group of nine individual muscles on the back of the forearm that act on the wrist and fingers. Collectively, their primary function is wrist extension, though they also help carry out other movements of the wrist and fingers. The individual wrist extensor muscles are as follows: Extensor carpi radialis longus …

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Posterior Deltoid: Functional Anatomy Guide

The posterior deltoid (L. posterior, behind ; deltoides, triangular) refers to the rear head of the three-headed deltoid muscle. It acts on the shoulder joint and is the prime mover in shoulder horizontal abduction. Located on the back of the shoulder – medial to the lateral deltoid and lateral to the middle trapezius – the posterior …

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Erector Spinae: Functional Anatomy Guide

The erector spinae (erigere, to erect ; spina, spine.) consists of three long, thin muscle groups running vertically up each side of the vertebral column: the iliocostalis, longissimus and spinalis. These muscles act on different segments of the vertebral column (i.e. lumbar, thoracic, cervical). Collectively, they are the prime movers in spinal extension and spinal lateral flexion. The …

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Internal Oblique: Functional Anatomy Guide

The internal oblique (L. internus, internal ; obliquus, oblique.) is a flat sheet of muscle on either the side of the lower torso. It gets its name from being beneath the external oblique and having an oblique fiber direction relative to the midline. The most prominent actions of the internal oblique are spinal lateral flexion and spinal rotation. Notably, …

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Pronator Teres: Functional Anatomy Guide

The pronator teres (L. pronus, lying face down ; teres, round and long.) is an elongated, cylindrical forearm muscle that crosses the gap between radius and ulna. It’s the strongest of the two pronator muscles. However, it is only active during rapid or resisted forearm pronation, which it carries out with help from the pronator quadratus. Notably, it also plays …

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Lateral Deltoid: Functional Anatomy Guide

The lateral deltoid (L. latus, side ; deltoides, triangular) is the outermost head of the deltoid and is primarily responsible for performing shoulder abduction. The lateral deltoid is part of the scapulohumeral (intrinsic shoulder) muscle group. It is situated between the anterior and posterior deltoid, and lies superficial to the insertions of the supraspinatus, infraspinatus and teres minor. It originates from the acromion process on …

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External Oblique Muscle: Functional Anatomy Guide

The external oblique (L. externus, external ; obliquus, oblique.) is a broad, flat sheet of muscle on either side of the abs. It is named after its location (external to the internal oblique) and its fiber direction (oblique relative to the midline of the body). It is the prime mover in spinal rotation, and it has a significant role in spinal lateral flexion. Notably, …

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Transversus Abdominis: Functional Anatomy Guide

The transversus abdominis (L. transversus, crosswise [trans, across ; vertere, to turn] ; abdo, to hide.) is a flat layer of muscle in the abdomen, whose fibers run transverse relative to the midline of the body. It is responsible for compressing the abdominal wall, helping to support and protect the internal organs, and assist in forced expiration. It also …

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Anterior Deltoid: Functional Anatomy Guide

The anterior deltoid (L. anterior, before, in front of ; deltoides, triangular) refers to the front head of the deltoid muscle. This part of the delt is responsible for shoulder flexion. Classified as part of the scapulohumeral (intrinsic shoulder) muscle group, the anterior deltoid is situated medial to the lateral deltoid and lateral to the clavicular head of …

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Triceps Brachii: Functional Anatomy Guide

Literally meaning the three-headed muscle of the arm, the triceps brachii (L. tres, three ; caput, head ; brachium, arm.) consists of a long, lateral and medial head. It is primarily responsible for elbow extension. Known commonly as just the triceps, it is twice as big as its counterpart, the biceps brachii, and thus accounts for …

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