Torso - Superficial Muscles of the Posterior Torso

teres minor

Teres Minor is a narrow muscle which lies below infraspinatus, above teres major and triceps brachii, and deep to deltoid. It is one of the four muscles which comprise the Rotator Cuff. Origin: The upper two-thirds of the lateral border of the scapula. Insertion: The upper fibres end in a tendon which inserts into the inferior facet of the greater tubercle of the humerus. The lower fibres insert into the humerus directly below the inferior facet of the greater tubercle of the humerus. Action: Teres Minor, along with Infraspinatus, primarily produces external rotation of the shoulder joint. It assists in adduction and extension of the shoulder. When the humerus is stabilized, abducts the inferior angle of the scapula. Function: In concert with the other rotator cuff muscles, Teres Minor is instrumental in providing stability to the shoulder joint, and helps to hold the humeral head in the glenoid cavity of the scapula.

latissimus dorsi

Latin: Musculus latissimus dorsi (plural: latissimi dorsi) Translation: meaning 'broadest [muscle] of the back' (Latin latus meaning 'broad', latissimus meaning 'broadest' and dorsum meaning the back) Origin: Spinous processes of vertebrae T7-L5, thoracolumbar fascia, iliac crest, inferior 3 or 4 ribs and inferior angle of scapula Insertion: Floor of intertubercular groove of the humerus Artery: Thoracodorsal branch of the subscapular artery Nerve: thoracodorsal nerve (C7,8) from the posterior cord of the brachial plexus Action: Adducts, extends and internally rotates the arm when the insertion is moved towards the origin. When observing the muscle action of the origin towards the insertion, the lats are a very powerful rotator of the trunk. Antagonist: Deltoid and trapezius muscle Description - is the larger, flat, dorso-lateral muscle on the trunk, posterior to the arm, and partly covered by the trapezius on its median dorsal region. Latissimi dorsi are commonly known as "lats", especially among bodybuilders. The latissimus dorsi is responsible for extension, adduction, transverse extension also known as horizontal abduction, flexion from an extended position, and (medial) internal rotation of the shoulder joint. It also has a synergistic role in extension and lateral flexion of the lumbar spine. Due to bypassing the scapulothoracic joints and attaching directly to the spine, the actions the latissimi dorsi have on moving the arms can also influence the movement of the scapulae, such as their downward rotation during a pull up. Structure - Variations: The number of dorsal vertebrae to which it is attached varies from four to eight; the number of costal attachments varies; muscle fibers may or may not reach the crest of the ilium. A muscular slip, the axillary arch, varying from 7 to 10 cm in length, and from 5 to 15 mm in breadth, occasionally springs from the upper edge of the latissimus dorsi about the middle of the posterior fold of the axilla, and crosses the axilla in front of the axillary vessels and nerves, to join the under surface of the tendon of the pectoralis major, the coracobrachialis, or the fascia over the biceps brachii. This axillary arch crosses the axillary artery, just above the spot usually selected for the application of a ligature, and may mislead a surgeon. It is present in about 7% of the population and may be easily recognized by the transverse direction of its fibers. Guy et al. extensively described this muscular variant using MRI data and positively correlated its presence with symptoms of neurological impingement. A fibrous slip usually passes from the upper border of the tendon of the Latissimus dorsi, near its insertion, to the long head of the triceps brachii. This is occasionally muscular, and is the representative of the dorsoepitrochlearis brachii of apes. This muscular form is found in ~5% of humans and is sometimes termed the latissimocondyloideus. The latissimus dorsi crosses the inferior angle of the scapula. A study found that, of 100 cadavers dissected: 43% had "a substantial amount" of muscular fibers in the latissimus dorsi originating from the scapula. 36% had few or no muscular fibers, but a "soft fibrous link" between the scapula and the latissimus dorsi 21% had little or no connecting tissue between the two structures. Triangles: The lateral margin of the latissimus dorsi is separated below from the obliquus externus abdominis by a small triangular interval, the lumbar triangle of Petit, the base of which is formed by the iliac crest, and its floor by the obliquus internus abdominis. Another triangle is situated behind the scapula. It is bounded above by the trapezius, below by the latissimus dorsi, and laterally by the vertebral border of the scapula; the floor is partly formed by the rhomboideus major. If the scapula is drawn forward by folding the arms across the chest, and the trunk bent forward, parts of the sixth and seventh ribs and the interspace between them become subcutaneous and available for auscultation. The space is therefore known as the triangle of auscultation. The latissimus dorsi can be remembered best for insertion as "The Lady Between Two Majors". As the latissimus dorsi inserts into the floor of the intertubercular groove of the humerus it is surrounded by two major muscles. The teres major inserts medially on the medial lip of the intertubercular groove and laterally the pectoralis major inserts into the lateral lip. Innervation: The latissimus dorsi is supplied by the sixth, seventh, and eighth cervical nerves through the thoracodorsal (long scapular) nerve. Electromyography suggests that it consists of six groups of muscle fibres that can be independently coordinated by the central nervous system. Function - * The latissimus dorsi is responsible for extension * adduction * transverse extension also known as horizontal abduction * flexion from an extended position * (medial) internal rotation of the shoulder joint. It also has a synergistic role in extension (posterior fibers) and lateral flexion (anterior fibers) of the lumbar spine, and assists as a muscle of both forced expiration (anterior fibers) and an accessory muscles of ispiration (posterior fibers). Most latissimus dorsi exercises concurrently recruit the teres major, posterior fibres of the deltoid, long head of the triceps brachii, among numerous other stabilizing muscles. Compound exercises for the 'lats' typically involve elbow flexion and tend to recruit the biceps brachii, brachialis, and brachioradialis for this function. Depending on the line of pull, the trapezius muscles can be recruited as well; horizontal pulling motions such as rows recruit both latissimus dorsi and trapezius heavily. Training - The power/size/strength of this muscle can be trained with a variety of different exercises. Some of these include: * Vertical pulling movements such as pull-downs and pull-ups (including chin-ups) * Horizontal pulling movements such as bent-over row, T-bar row and other rowing exercises * pull-overs * deadlift Lifting under control can help reduce chances of injury. Clinical relevance - Tight latissimus dorsi has been shown to be one cause of chronic shoulder pain and chronic back pain. Because the latissimus dorsi connects the spine to the humerus, tightness in this muscle can manifest as either: sub-optimal glenohumeral joint (shoulder) function which leads to chronic pain. Or tendinitis in the tendinous fasciae connecting the latissimus dorsi to the thoracic and lumbar spine. The latissimuus dorsi is a potential source of muscle for breast reconstruction surgery after mastectomy or to correct pectoral hypoplastic defects such as Poland's syndrome. An absent or hypoplastic latissimus dorsi can be one of the associated symptoms of Poland's syndrome. Cardiac support: For heart patients with low cardiac output and who are not candidates for cardiac transplantation, a procedure called cardiomyoplasty may support the failing heart. This procedure involves wrapping the latissimus dorsi muscles around the heart and electrostimulating them in synchrony with ventricular systole.

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Muscles of the Posterior Torso

rhomboideus (major)

Latin: musculus rhomboideus major Origin: spinous processes of the T2 to T5 vertebrae Insertion: medial border of the scapula, inferior to the insertion of rhomboid minor muscle Artery: dorsal scapular artery Nerve: dorsal scapular nerve (C4 and C5) Actions: Retracts the scapula and rotates it to depress the glenoid cavity. It also fixes the scapula to the thoracic wall. Antagonist: Serratus anterior muscle Description: The rhomboid major is a skeletal muscle on the back that connects the scapula with the vertebrae of the spinal column. In human anatomy, it acts together with the rhomboid minor to keep the scapula pressed against thoracic wall and to retract the scapula toward the vertebral column. Structure: The rhomboid major arises from the spinous processes of the thoracic vertebrae T2 to T5 as well as the supraspinous ligament. It inserts on the medial border of the scapula, from about the level of the scapular spine to the scapula's inferior angle. The rhomboid major is considered a superficial back muscle. It is deep to the trapezius, and is located directly inferior to the rhomboid minor. As the word rhomboid suggests, the rhomboid major is diamond-shaped. The major in its name indicates that it is the larger of the two rhomboids. Variation: The two rhomboids are sometimes fused into a single muscle. Innervation: The rhomboid major, like the rhomboid minor, is innervated by the ventral primary ramus via the dorsal scapular nerve (C5). Artery: Both rhomboid muscles also derive their arterial blood supply from the dorsal scapular artery. Function: The rhomboid major helps to hold the scapula (and thus the upper limb) onto the ribcage. Other muscles that perform this function include the serratus anterior and pectoralis minor. Both rhomboids (major and minor) also act to retract the scapula, pulling it towards the vertebral column. The rhomboids work collectively with the levator scapulae muscles to elevate the medial border of the scapula, downwardly rotating the scapula with respect to the glenohumeral joint. Antagonists to this function (upward rotators of the scapulae) are the serratus anterior and upper and lower fibers of the trapezius. If the lower fibers are inactive, the serratus anterior and upper trapezii work in tandem with rhomboids and levators to elevate the entire scapula. Clinical significance: If the rhomboid major is torn, wasted, or unable to contract, scapular instability may result. The implications of scapular instability caused by the rhomboid major include scapular winging during scapular protraction, excessive lateral rotation and depression of the scapula, as the antagonistic action of the rhomboid major is absent. With scapular instability, movement in the upper extremity is limited as the scapula cannot guide the desired movement of the arm and shoulders. Pain, discomfort, and limited range of motion of the shoulder are possible implications of scapular instability. Treatment for scapular instability may include surgery followed by physical therapy or occupational therapy. Physical therapy may consist of stretching and endurance exercises of the shoulder. Pilates and yoga have been also suggested as potential treatment and prevention of scapular instability.

deltoid

Latin: musculus deltoideus Origin: the anterior border and upper surface of the lateral third of the clavicle, acromion, spine of the scapula Insertion: deltoid tuberosity of humerus Artery: thoracoacromial artery, anterior and posterior humeral circumflex artery Nerve: Axillary nerve Actions: shoulder abduction, flexion and extension Antagonist: Latissimus dorsi 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). Description - 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. Deltoid is also further shortened in slang as "delt". Structure - The deltoid originates in three distinct sets of fibers, often referred to as "heads" 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 are commonly called front 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. This muscle is also called middle delts, outer delts, or side delts for short. They are also mistakenly called medial deltoid, 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 or rear deltoid (rear delts for short. 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. Insertion From this extensive origin the fibers converge toward their insertion on the deltoid tuberosity on the middle of the lateral aspect of the shaft of the humerus; the middle fibers passing vertically, the anterior obliquely backward and laterally, and the posterior obliquely forward and laterally. Though traditionally described as a single insertion, the deltoid insertion is divided into two or three discernible areas corresponding to the muscle's three areas of origin. The insertion is an arch-like structure with strong anterior and posterior fascial connections flanking an intervening tissue bridge. It additionally gives off extensions to the deep brachial fascia. Furthermore, the deltoid fascia contributes to the brachial fascia and is connected to the medial and lateral intermuscular septa. Blood supply: The deltoid is supplied by the posterior circumflex humeral artery and the deltoid branch of the thoracoacromial artery which branches from the axillary artery. Innervation: The deltoid is innervated by the axillary nerve. The axillary nerve originates from the anterior rami of the cervical nerves C5 and C6, via the superior trunk, posterior division of the superior trunk, and the posterior cord of the brachial plexus.[citation needed] The axillary nerve is sometimes damaged during operations on the axilla, such as for breast cancer. It may also be injured by anterior dislocation of the head of the humerus.[citation needed] Function: When all its fibers contract simultaneously, the deltoid is the prime mover of arm abduction along the frontal plane. The arm must be medially rotated for the deltoid to have maximum effect. This makes the deltoid an antagonist muscle of the pectoralis major and latissimus dorsi during arm adduction. The anterior fibers are involved in shoulder abduction when the shoulder is externally rotated. The anterior deltoid is weak in strict transverse flexion but assists the pectoralis major during shoulder transverse flexion / shoulder flexion (elbow slightly inferior to shoulders). The anterior deltoid also works in tandem with the subscapularis, pecs and lats to internally (medially) rotate the humerus. The posterior fibers are strongly involved in transverse extension particularly as the latissimus dorsi is very weak in strict transverse extension. Other transverse extensors, the infraspinatus and teres minor, also work in tandem with the posterior deltoid as external (lateral) rotators, antagonists to strong internal rotators like the pecs and lats. The posterior deltoid is also the primary shoulder hyperextensor, more so than the long head of the triceps which also assists in this function. The lateral fibers perform basic shoulder abduction when the shoulder is internally rotated, and perform shoulder transverse abduction when the shoulder is externally rotated. They are not utilized significantly during strict transverse extension (shoulder internally rotated) such as in rowing movements, which use the posterior fibers. An important function of the deltoid in humans is preventing the dislocation of the humeral head when a person carries heavy loads. The function of abduction also means that it would help keep carried objects a safer distance away from the thighs to avoid hitting them, as during a farmer's walk. It also ensures a precise and rapid movement of the glenohumeral joint needed for hand and arm manipulation. The lateral fibers are in the most efficient position to perform this role, though like basic abduction movements (such as lateral raise) it is assisted by simultaneous co-contraction of anterior/posterior fibers. The deltoid is responsible for elevating the arm in the scapular plane and its contraction in doing this also elevates the humeral head. To stop this compressing against the undersurface of the acromion the humeral head and injuring the supraspinatus tendon, there is a simultaneous contraction of some of the muscles of the rotator cuff: the infraspinatus and subscapularis primarily perform this role. In spite of this there may be still a 1-3 mm upward movement of the head of the humerus during the first 30° to 60° of arm elevation. Clinical significance: The most common abnormalities affecting the deltoid are tears, fatty atrophy, and enthesopathy. Deltoid muscle tears are unusual and frequently related to traumatic shoulder dislocation or massive rotator cuff tears. Muscle atrophy represents the end result of many causes, including aging, disuse, denervation, muscular dystrophy, cachexia and iatrogenic injury. Deltoideal humeral enthesopathy is an exceedingly rare condition related to mechanical stress. Conversely, deltoideal acromial enthesopathy is likely a hallmark of seronegative spondylarthropathies and its detection should probably be followed by pertinent clinical and serological investigation.

supraspinatus

Supraspinatus is the smallest of the 4 muscles which comprise the Rotator Cuff of the shoulder joint specifically in the supraspinatus fossa. It travels underneath the acromion. Origin: Supraspinatus fossa of the scapula. A shallow depression in the body of the scapula above its spine. Insertion: Greater tuberosity of the humerus, superior facet. Action: It abducts the arm from 0 to 15 degrees, when it is the main agonist, then assists deltoid to produce abduction beyond this range up to 90 degrees. Function: Shoulder Stability - As part of the Rotator Cuff, supraspinatus helps to resist the gravitational forces which act on the shoulder joint to pull from the weight of the upper limb downward. It also helps to stabilize the shoulder joint by keeping the head of the humerus firmly pressed medially against the glenoid fossa of the scapula.

erector spinae group

The erector spinæ is a muscle group of the back in humans and other animals, which extends the vertebral column (bending the spine such that the head moves posteriorly while the chest protrudes anteriorly). It is also known as sacrospinalis in older texts. A more modern term is extensor spinae, though this is not in widespread use. The erector spinæ is not just one muscle, but a bundle of muscles and tendons. It is paired and runs more or less vertically. It extends throughout the lumbar, thoracic and cervical regions, and lies in the groove to the side of the vertebral column. Erector spinæ is covered in the lumbar and thoracic regions by the thoracolumbar fascia, and in the cervical region by the nuchal ligament. This large muscular and tendinous mass varies in size and structure at different parts of the vertebral column.

gluteus medius

The gluteus medius, one of the three gluteal muscles, is a broad, thick, radiating muscle, situated on the outer surface of the pelvis. Its posterior third is covered by the gluteus maximus, its anterior two-thirds by the gluteal aponeurosis, which separates it from the superficial fascia and integument. Structure: The gluteus medius muscle starts, or "originates," on the outer surface of the ilium between the iliac crest and the posterior gluteal line above, and the anterior gluteal line below; the gluteus medius also originates from the gluteal aponeurosis that covers its outer surface. The fibers of the muscle converge into a strong flattened tendon that inserts on the lateral surface of the greater trochanter. More specifically, the muscle's tendon inserts into an oblique ridge that runs downward and forward on the lateral surface of the greater trochanter.

lumbar aponeurosis

The lumbar aponeurosis is not a muscle. An aponeurosis, as previously stated, is a white, flattened tendinous expansion, serving mainly to connect a muscle with the parts that it moves. It replaces what were formerly called fasciae (plural), although some doctors and dictators may still use the old terminology. The posterior lumbar aponeuroses are situated just on top of the epaxial muscles of the thorax, which are multifidus spinae and Sacrospinalis.

teres major

The teres major muscle (Latin teres meaning 'rounded') is a muscle of the upper limb and one of seven scapulohumeral muscles. It is a thick but somewhat flattened muscle, innervated by the lower subscapular nerve (C5 and C6). Structure: It arises from the oval area on the dorsal surface of the inferior angle of the scapula, and from the fibrous septa interposed between this muscle and the rotator cuff lateral rotator pair of the teres minor and infraspinatus. The fibers of teres major insert into the medial lip of the intertubercular sulcus of the humerus. Function: The teres major is a medial rotator and adductor of the humerus and assists the latissimus dorsi in drawing the previously raised humerus downward and backward (extension, but not hyper extension). It also helps stabilize the humeral head in the glenoid cavity.

trapezius

The trapezius is either one of two large superficial muscles that extend longitudinally from the occipital bone to the lower thoracic vertebrae and laterally to the spine of the scapula (shoulder blade). Its functions are to move the scapulae and support the arm. The trapezius has three functional regions: the superior region (descending part), which supports the weight of the arm; the intermediate region (transverse part), which retracts the scapulae; and the inferior region (ascending part), which medially rotates and depresses the scapulae.

infraspinatus

the infraspinatus muscle is a thick triangular muscle, which occupies the chief part of the infraspinatous fossa. As one of the four muscles of the rotator cuff, the main function of the infraspinatus is to externally rotate the humerus and stabilize the shoulder joint. It attaches medially to the infraspinous fossa of the scapula and laterally to the middle facet of the greater tubercle of the humerus. Function: The infraspinatus is the main external rotator of the shoulder. When the arm is fixed, it abducts the inferior angle of the scapula. Its synergists are teres minor and the deltoid. The infraspinatus and teres minor rotate the head of the humerus outward (external, or lateral, rotation); they also assist in carrying the arm backward. Additionally, the infraspinatus reinforces the capsule of the shoulder joint