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 … Read more
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 … Read more
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 … Read more
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, … Read more
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 … Read more
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 … Read more
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 … Read more
The infraspinatus (L. infra, below ; spinus, spine [of scapula]) is a thick rotator cuff muscle covering the majority of the posterior surface of the shoulder blade below the scapular spine. It is a prime mover in shoulder external rotation and plays important roles in shoulder stability. Most notably, it prevents excessive anterior and posterior … Read more
The wrist flexors refer to six muscles in the anterior compartment of the forearm that act on the wrist and finger joints. As a group, the primary action of the wrist flexors is, you guessed it… wrist flexion! As I’ll detail later, these muscles are also responsible for other movements of the fingers and wrist. Each of … Read more
The levator scapulae (L. levator, elevator ; scapulae, shoulder blades.) is a strap-like muscle in neck and shoulder region. It acts on the scapula and cervical spine, and as its name reveals, its most prominent role is scapular elevation. Classified as a superficial posterior axioappendicular (extrinsic shoulder) muscle, the levator scapulae is situated deep to … Read more