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The deltoide muscle (Latin deltoideus) is the largest muscle in the shoulder area. It lies superficially and is visible through the skin. It has the shape of a triangle pointing downwards. It resembles the inverted Greek letter delta, from which the Latin name comes from.
The deltoid muscle is flat and relatively thick (up to 2 cm). It surrounds the shoulder joint and as the only muscle in the shoulder areait starts on both bones of the upper limb girdle(collarbone and scapula). The rest of the muscles in this area (mm. Supraspinatus, infraspinatus, lesser curl, greater capillary and subscapular), which alsoconnect the rim to the humerus, beginon the shoulder blade.
Deltoid muscle - structure
The deltoid muscle has three initial trailers, therefore it is divided into three parts:
- anterior part( collarbone ) starts at the shoulder end of the collarbone;
- medial part( shoulder ) starts at the shoulder process of the scapula;
- posterior part( comb ) has an initial attachment on the lower edge of the scapular crest, where it also connects to the fascia that covers the infraspinatus.
The muscle fibers of the anterior and posterior sections run parallel downwards and to the side, while the fibers of the medial section follow lateral directions to form an arch over the greater tubercle of the humerus and follow it downwards. All three parts end in a strong tendon atshoulder tuberosity of the humerus(Latin: Tuberositas deltoidea), next to and slightly below the greater pectoralis (Latin pectoralis major). The end tendon cuts with a wedge into the attachment area of the initial brachialis (Latin brachialis).
The shoulder part of the deltoid muscle is pinnate , which means that it has a large number of muscle fibers and a large physiological cross-section. As a result, it creates a characteristic prominent protrusion in the shoulder area, covering the proximal end of the humerus, especially its larger tubercle. The deltoid model lies superficially, which means that it covers not only the shoulder joint, but also the muscles that begin around it and the surrounding bone parts.
Between the deltoid and the greater tubercle of the humerus there is a largesynovial bursa(Latin bursasubdeltoidea). Sometimes it connects to the bursa located higher, under the shoulder process (Latin bursa subacromialis). Sometimes there is also a subcutaneous synovial bursa on the shoulder process.
Between the initial attachment of the deltoid muscle and the end attachment of the trapezius (Latin trapezius) there is a separatingbone streakwhich is formed by the collarbone, shoulder process and crest of the scapula. The posterior edge of the deltoid muscle crosses with mm. subcapsular, rounded smaller, rounded larger and triceps (Latin triceps brachii). The anterior edge borders on the greater pectoral muscle (Latin pectoralis major), which is usually separated from it by the deltoid-thoracic furrow, but sometimes these muscles are partially fused together.
Blood is supplied by the deltoid artery departing fromthe axillary artery by the posterior artery surrounding the armandthe deltoid branch of the thoracic-brachial artery .axillary nerve(C5-C6) is responsible for the innervation of the deltoid nerve.
Deltoid - Feature
Individual parts of the deltoid function have different functions:
- medial part(shoulder)abducts the arm in the shoulder joint to 90 degreesin relation to the body. In this position, the humerus is in contact with the shoulder process and movement in the joint in that direction is blocked. Raising the arm above this level is done in the collarbones;
- anterior(collarbone)turns the arm inward and brings it forward ;
- back(crest)turns arm outward and backward .
Deltoid - pain
The deltoid pain most often occurs during the shoulder abduction movement, although there are also overloads and injuries of the anterior or posterior part, which are painful and tender during the adduction of the upper limb. The most common causes of shoulder pain are:
- overload;
- irritation;
- over voltage;
- mechanical injuries.
The deltoid muscle itself, however, is not often the source of shoulder pain. When it occurs, it is also worth checking other potential causes of pain, which may be:
- inflammation of the subacial bursa;
- sub-shoulder gap syndrome;
- damage to the rotator cuff;
- frozen shoulder syndrome;
- painful shoulder syndrome;
- degenerative changes within the joints forming the shoulder complex;
- tendinitis of the biceps brachii;
- upper intersection complex.
Muscleshoulder - exercises
The deltoid exercises vary depending on which part of the muscle you want to train. The resistant abduction movement (using dumbbells or rubber bands) will stimulate the work of the middle part. Adding the upper limb and dragging it forward with resistance (for example, pressing weights on a bench) will strengthen the front part. And the dragging of the arm backwards will be training for the posterior part.
The deltoid muscle is relatively strong because it operates with a rather heavy upper limb, but it is not one of the most durable structures that can sustain prolonged tension. Therefore, it is more effective with dynamic effort, which does not mean that it cannot be practiced in a different range. After strength or endurance training, you should also stretch your muscles.
Bibliography
Bochenek A., Reicher M., "Human Anatomy", volume I, PZWL Medical Publishing, Warsaw 2012.