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The deltoid muscle, often shortened to delt in slang, is a large, triangular-shaped muscle that forms the rounded contour of the human shoulder. It is a key shoulder stabilizer and is responsible for lifting the arm to the front, side, and back. Deltoid muscles are extremely mobile and can move in almost any direction without restrictions. They are also susceptible to injury, with tears and strains being common issues.
| Characteristics | Values |
|---|---|
| Common name | Deltoid muscle |
| Slang name | Delt |
| Description | A large, triangular-shaped muscle that forms the rounded contour of the shoulder |
| Location | The upper body, where the upper arm meets the torso |
| Function | Allows the arm to lift to the front, side and back |
| Blood supply | Axillary artery, including the thoracoacromial artery, circumflex humeral arteries, profunda brachii artery, and deep brachial artery |
| Nerve supply | Axillary nerve |
| Composition | Three distinct sets of muscle fibres: anterior or clavicular, posterior or scapular, and intermediate or acromial |
| Weight | Average of 192 grams, ranging from 84 grams to 366 grams |
| Conditions | Adhesive capsulitis, axillary nerve palsy, bursitis, deltoid fibrosis, rotator cuff tears, shoulder impingement syndrome, shoulder separation, strains, tendonitis |
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What You'll Learn
Delt anatomy
The deltoid muscle, often shortened as "delt", is a large, triangular-shaped muscle that forms the rounded contour of the human shoulder. It is a key shoulder stabilizer, preventing inferior glenohumeral joint displacement and dislocations. The deltoid is responsible for elevating the arm in the scapular plane, and its contraction also elevates the humeral head. It is a superficial muscle overlying the glenohumeral joint and is one of the six intrinsic muscles of the shoulder.
The deltoid is comprised of three distinct portions: the anterior or clavicular (commonly known as the front delt), the middle or acromial (side delt), and the posterior or spinal (rear delt). These three parts form a triangular muscle, with the anterior and posterior portions being unipennate, and the lateral region being multipennate. The deltoid originates from the scapular spine, superior acromial surface, and lateral third of the clavicle. The deltoid's proximal attachment is U-shaped, mirroring the trapezius muscle's distal insertion.
The deltoid muscle fibres run laterally and inferiorly towards the humerus, converging into a narrow base that attaches to the deltoid tuberosity of the humerus. The anterior part attaches to the lateral third of the clavicle, the lateral part attaches to the acromion process, and the posterior part attaches to the spine of the scapula.
The deltoid muscle is supplied by the thoracoacromial artery, the circumflex humeral arteries, and the profunda brachii artery. It is innervated by the axillary nerve, which runs around the neck of the humerus once exiting the axilla. The axillary nerve is susceptible to injury during shoulder dislocation or fracture of the surgical neck of the humerus, which can lead to paralysis of the deltoid muscle.
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Delt functions
The deltoid muscle, often shortened as "delt", is a large, triangular-shaped muscle that forms the rounded contour of the human shoulder. It is one of the main abductors of the shoulder, helping to lift the arm to the front, side, and back. The deltoid is a key shoulder stabilizer, preventing inferior glenohumeral joint displacement and dislocations. It is also responsible for elevating the arm in the scapular plane, with a simultaneous contraction of some of the muscles of the rotator cuff.
The deltoid is a complex muscle group located where the upper arm meets the torso. It is connected with many other muscles and bones in the upper back, neck, and shoulder region. The deltoid is made up of three distinct sets of muscle fibres: the anterior or clavicular part (commonly known as the front delt), the posterior or scapular part (commonly known as the rear delt), and the intermediate or acromial part (commonly known as the side delt). These three parts form a triangular muscle with a U-shaped proximal attachment, mirroring the trapezius muscle's distal insertion. The deltoid distally attaches to the deltoid tuberosity of the humerus.
The deltoid muscle fibres run laterally and inferiorly towards the humerus and converge into a narrow base that attaches to the bone. When the three parts of the deltoid contract simultaneously, it results in abduction of the shoulder when the arm is already held at 15 degrees of abduction. Each part of the deltoid muscle can also contract independently, producing other arm movements. For example, when the anterior deltoid contracts alone, it produces extension and lateral rotation of the arm, and when the lateral part of the deltoid contracts independently, it causes the arm to abduct.
The deltoid muscle is supplied by the thoracoacromial artery and its branches, the circumflex humeral arteries, and the profunda brachii artery. It is innervated by the axillary nerve, which can be damaged during surgery or due to trauma or overuse of a crutch, leading to shoulder weakness or numbness. The deltoid is a common site for intramuscular injections and is often used in surgery to correct shoulder defects.
The deltoid muscle is prone to injuries due to its high mobility and minimal bone attachments. Deltoid muscle tears are uncommon but can result from massive rotator cuff tears or traumatic shoulder dislocations. Strains can also occur from overuse or repetitive overhead activities, such as swimming, painting, or playing water polo. Certain exercises and routines can help keep the deltoids strong and flexible to prevent injuries.
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Delt injuries
The deltoid muscle, often shortened to "delt", is a large, triangular muscle that forms the rounded contour of the human shoulder. It is divided into three distinct sets of muscle fibres: the anterior or clavicular part (front delt), the posterior or scapular part (rear delt), and the intermediate or acromial part (side delt). The deltoid muscle is responsible for lifting the arm and giving the shoulder its range of motion.
Deltoid injuries are common and can be caused by overuse or injury. They are graded based on severity, from Grade 1 (mild pain and minimal swelling) to Grade 3 (severe pain, swelling, and a muscle bulge or gap). Recovery time depends on the severity of the injury, ranging from one to two weeks for minor strains to up to four months for serious tears.
Deltoid strains can be caused by several mechanisms, most commonly overuse of the muscle without adequate rest. This can lead to discomfort in the area of the deltoid muscle, with associated swelling and loss of function. Other causes include forced eccentric contraction of the shoulder (lengthening of the muscle belly while contracting) and, less commonly, a direct traumatic blow to the shoulder.
To prevent deltoid injuries, it is important to warm up before exercising, stretch daily to improve range of motion and flexibility, rest after exercising, and strengthen the deltoid and core muscles.
Treatment for deltoid strains depends on the severity of the injury. For Grade 1 strains, doctors may recommend using a compression wrap and applying ice for 24 hours after the injury. For Grade 2 strains, applying ice for 3-5 days can help reduce swelling, and alternating between ice and heat packs can relieve pain. Grade 3 strains may require over-the-counter painkillers to reduce discomfort, and it is important to elevate the affected arm when possible and avoid using it.
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Delt pain
The deltoid muscle, often shortened as "delt", is a large triangular muscle that forms the rounded contour of the human shoulder. It is responsible for lifting the arm and giving the shoulder its range of motion. The deltoid muscle is a common site for intramuscular injections and vaccinations.
Deltoid muscle pain or rear shoulder pain can be caused by a variety of conditions or injuries, but they generally all involve overuse of the deltoid muscle. Deltoid pain can be centred on the front, side, or back of the shoulder, or all of the above. It can be caused by a number of factors, including:
- Overuse injuries and strains: This is the most common cause of deltoid pain. It can be caused by repetitive overhead arm movements, such as swimming, pitching, or throwing overhead.
- Tendonitis: Shoulder tendonitis occurs when the tendons in the shoulder become inflamed. This can cause pain in the deltoid muscle and make it difficult to use the shoulder muscles or move the joint.
- Rotator cuff tears: Severe rotator cuff tears can damage or dislocate the deltoid muscle.
- Shoulder impingement syndrome: This occurs when the shoulder muscles or tendons rub against the bones, causing friction and leading to joint pain and inflammation.
- Frozen shoulder: This condition causes stiffness or even inability to move the shoulder after an injury. Adhesions develop and tighten or "freeze" the shoulder, causing pain in the general shoulder joint region.
- Axillary nerve palsy: Compression or damage to the axillary nerve can lead to shoulder weakness or numbness, especially around the deltoid muscle.
- Bursitis: This is an inflammation of the bursa (tiny, fluid-filled sacs) in the shoulders, which can make it hard to move the shoulder joint and cause muscle irritation.
To relieve deltoid pain, there are several treatments that can be considered:
- Adjusting exercise routines: For mild injuries caused by overuse, decreasing the intensity and duration of workouts or sports practices can help the shoulders heal.
- Anti-inflammatories: Over-the-counter anti-inflammatories, such as ibuprofen or naproxen, can help reduce inflammation, swelling, and discomfort.
- Ice and heat therapy: Applying ice and heat packs alternately can help reduce swelling and relieve pain.
- Rest: Allowing the shoulder to rest and avoiding using the affected arm and shoulder can aid in recovery.
- Stretching: Gentle stretching can help reduce pain and prevent future injuries.
- Sleeping position: Sleeping on the back or the opposite side of the painful shoulder can help ease deltoid pain while sleeping.
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Delt treatments
The deltoid muscle, often shortened to "delt", is a large triangular muscle that forms the rounded contour of the human shoulder. It is divided into three distinct parts: the anterior (front) deltoid, the middle deltoid, and the posterior (back) deltoid. Each part is responsible for a different type of movement. The anterior deltoid is responsible for shoulder flexion, the middle deltoid is responsible for abduction, and the posterior deltoid is responsible for shoulder extension. The deltoid muscle is a key stabiliser of the shoulder joint and helps to provide strength for the shoulder.
There are several conditions that can affect the deltoid muscle. These include adhesive capsulitis (frozen shoulder), axillary nerve palsy, bursitis, deltoid fibrosis, rotator cuff tears, shoulder impingement syndrome, shoulder separation, strains and overuse injuries, tendonitis, tears, fatty atrophy, and enthesopathy. Most deltoid muscle injuries can be treated non-surgically. Treatments for mild injuries include adjusting exercise routines, reducing the intensity and duration of workouts, and using over-the-counter anti-inflammatories such as ibuprofen or naproxen. For a Grade 1 deltoid strain, it is recommended to use a compression wrap and apply ice for 24 hours after the injury, followed by a heating pad to relieve pain and tension. Other non-surgical treatments include physical therapy, shoulder exercises, slings or other supportive garments, and steroid injections. In more severe cases, surgery may be required, such as in serious muscle tears or to correct shoulder defects arising from breast cancer treatment.
To prevent deltoid pain and shoulder injuries, it is important to warm up sufficiently before beginning a workout and to take rest days to allow the muscle to recover. Sports massages can also help to relieve tension in the muscles. Specific exercises to strengthen the deltoid muscle include shoulder presses, lateral raises, and rear deltoid raises. It is important to perform these exercises correctly to ensure the muscle is being properly worked and the shoulder joint is stabilised.
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Frequently asked questions
The deltoid muscle, also known as the delt, is a large triangular-shaped muscle that forms the rounded contour of the human shoulder. It is a key shoulder stabilizer and is responsible for lifting the arm to the front, side and back.
The deltoid muscle is made up of three distinct sets of muscle fibres: the anterior or clavicular part (front delt), the posterior or scapular part (rear delt), and the intermediate or acromial part (side delt).
The deltoid muscle is responsible for abduction of the shoulder, as well as flexion and extension movements of the arm. It also assists in forward elevation of the arm and helps prevent dislocation of the glenohumeral joint.
Common conditions affecting the deltoid muscle include rotator cuff tears, shoulder impingement syndrome, shoulder separation, strains and overuse injuries, tendonitis, and bursitis.
To keep your deltoid muscles healthy and strong, it is important to perform exercises and routines guided by a fitness instructor. This can help improve flexibility and reduce the risk of injuries.
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