Muscles which abduct the shoulder

Get your questions answered right away, and find out which Study Program is right for you! Call or Chat now! Everything you want to know about our top-rated Study Programs are just a call or click away. As a fitness professional and an exam candidate, there is no way of getting around the fact that you need to know your anatomy! Understanding how the body moves and creates movement with the muscles is a huge part of the job. In an earlier blog, we looked at how to study anatomy. We then started breaking down each body part, with the last blog looking at the muscles that move the scapulae.

The glenohumeral joint—commonly referred to as the shoulder joint—consists of the attachment of the humerus bone to the scapula. Many actions occur at this ball-and-socket joint. From the anatomical position, rotate your arm so that the elbow faces forward. This action at the shoulder can occur when your arm is in different positions flexion, abduction, etc. From a position of internal shoulder rotation, rotate your arm so that the elbow faces backward.

Also, anatomical position requires the shoulders to be in external rotation. For the start postion, lift your arms in front of you. The action occurs as you then move your arms out to the side. From the starting position, lift your arms out to the side. The actions occurs as you then move your arms in front of you. The elbow joint consists of the humerus, radius and ulna bones.

The two main actions at the elbow are flexion and extension. The wrist joint consists of the distal ends of the radius and ulna and the carpal bones of the hand. The two main actions of the wrist are flexion and extension. A helpful way to learn anatomy is to move and mimic the actions for the muscles you are learning that week. Look at the picture of the muscle, find it on your body, and picture how it is contracting as it produces its associated movement or movements.

That is, contract the muscle you are reviewing and complete the different actions that the muscle is capable of making. Sign up to receive relevant, science-based health and fitness information and other resources. Don't miss out! The tendons of these muscle coalesce to form the rotator cuff. The muscles are inseparable at this level, except for subscapularis which is separate and joined to the rest of the cuff via the rotator interval.

Supraspinatus is not only an initiator of abduction, but acts throughout the range of abduction of the shoulder. It has equal abduction power as deltoid.

Note that it lies in the scapular plane - i. These two muscles lies below the scapular spine and are external rotators of the shoulder. Infraspinatus primarily acts with the arm in neutral and Teres Minor is more active with external rotation in 90 degrees of abduction.

Subscapularis is the main internal rotator of the shoulder. It is a passive restraint in neutral, but not abduction. The deltoid muscle is the only shoulder elevator if the supraspinatus is torn and dysfunctional.

Therefore most rehabilitation is directed towards this muscle. It comprises anteriormiddle and posterior portions which are more active depending on the direction of arm elevation. Anterior view of deltoid Posterior view of deltoid. In this diagram, with the arm fully extended the deltoid has to counteract the weight of the arm and a 25kg weight in the person's hand. Moments pulling humerus down:. Now if the person bends his elbow, reducing the moment arm of the 25kg weight and arm the force required of deltoid to elevate the arm will be reduced.

A force acting on a body has two effects, one to move it and two to rotate it. However, a body may rotate without moving. A force couple is a system that exerts a resultant movement, but no resultant force. Two equal and opposite forces exert a purely rotation force.

In the shoulder the body is the humeral head and the equal but opposite forces are the rotator cuff muscles. The rotator cuff muscles act as a force couple with each other and the deltoid.

The rotator cuff muscles work together to contain the glenohumeral joint, which is an inherently unstable joint. The progression of a rotator cuff tear or dysfunction leads to superiorsubluxation of the humeral head.

This leads to dysfunction of the shoulder. The rotator cuff stabilises the glenohumeral joint through force couples in both the coronal and transverse planes. Deltoid and supraspinatus both contribute to abduction equally.

As the arm is abducted the resultant joint reaction force is directed towards the Glenoid. This 'compresses' the humeral head against the Glenoid and improves the stability of the joint when the arm is abducted and overhead. J Orthop Res. Throughout the range of motion the compressive resultant joint reaction force in the transverse plane contributes to joint stability. This is the predominant mechanism resisting superiorhumeral head displacement with cuff tears.

As long as the force couple between subscapularis and Infraspinatus remains balanced the joint remains centred. In addition to the dynamic stabilisers mentioned above, there are important secondary restraints to superior displacement of the humeral head with cuff tears.

The coraco-acromial arch is the combination of the coracoid, coracoacromial ligament and acromion. These form an arch above the rotator cuff and humeral head. The long head of biceps passes over the humeral head curving in two planes forming the shape of a question mark. It is recognised as providing a small degree of stability to the gleno-humeral joint. JBJSB, ]. The biceps pulley is a stabiliser of the long head of biceps in the biceps groove.

Rupture of this pulley with a rotator cuff tear leads to medial subluxation of the long head of biceps and dysfunction. The fusing of the rotatorcuff tendons suggests that they act more as a combined and integrative structure than as single entities. The microstructure of the rotator cuff tendons near the insertions of the supraspinatus and infraspinatus has been further described as a five-layer structure:. The fibre orientation also differs along the length of the rotator cuff tendon.

Near the musculotendinous junctions, the tendons are composed mainly of parallel homogeneous collagen fibers but become flat ribbonlike bundles of fibers that cross at an angle of about 45 degrees as they reach insertion into the humerus [Gohlke et al. Because of the various fiber orientations and distinct layers within the superiorcapsular complex, significant shear forces likely exist and may have a role in cuff tears.

These intratendinous variations in the cuff structure may explain why intrasubstance tears occur. Shear forces are probably directed to layer four, which is the site of development of intratendonous cuff tears. These tend to be degenerate tears of the cuff.

The midsubstance of the supraspinatustendon is primarily composed of Type I collagen, with relatively small amounts of Type III collagen, decorin, and biglycan. The fibrocartilage portion of the insertion has a collagen and proteoglycan content similar to that of tissues that have been subjected to compressive loads. This is partly due to the wrapping of thetendon around the humerus. Therefore, it mainly contains Type II collagen and larger proteoglycans such as aggrecan. The histological organization, however, does not resemble mature fibrocartilage.

In rotator cuff tendinopathy, an increase in collagen Type III, a protein that plays a role in healing and repair, and glycosaminoglycan and proteoglycan content has been observed.

These compositional changes may be adaptive, pathologic, or both, and are found to be altered in the older population. Furthermore, recent studies have shown increased levels of smooth muscle actin SMA in torn rotator cuffs. SMA-positive cells have been shown to contract a collagen-glycosaminoglycan analog in vitro. SMA-containing cells in rotator cuff tears may react with the high levels of GAG and proteoglycan resulting in retraction of the ruptured rotator cuff and inhibition of potential healing.

The major arterial supply to the rotator cuff is derived from the ascending branch of the anterior humeral circumflex artery, the acromial branch of the thoracoacromial artery, as well as the suprascapular and posterior humeral circumflex arteries.

The pathogenesis of rotator cuff tears has been considered to be influenced by the microvascular supply of the rotator cuff tendons. Most cadaver studies have demonstrated a hypovascular area within the critical zone of the supraspinatustendon. It has been suggested that this area of hypovascularity has a significant role in the attritional degeneration of the aging tendon. More recent studies of the microvascular supply to the supraspinatus tendon in symptomatic patients with impingement syndrome suggest that in the area of greatest impingement, i.

In vivo analysis using orthagonal polarisation spectral imaging has demonstrated that there is good vascularity of supraspinatus, even in the critical zone in intact rotator cuffs [ Biberthaler et al.