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The deltoid muscle is a large, triangular-shaped muscle that sits over the shoulder joint and gives the shoulder its rounded contour. It is a powerful muscle that is used in many athletic activities and everyday activities such as lifting or reaching. The deltoid is the primary muscle responsible for horizontal shoulder abduction, a movement that helps strengthen the shoulder and upper back muscles, promoting good posture and reducing the risk of injuries. Other muscles involved in horizontal abduction include the trapezius muscles (UT, MT, and LT) and the pectoralis minor muscle.
| Characteristics | Values |
|---|---|
| Targeted Muscles | Shoulder and upper back muscles |
| Muscle Activity | The activity of the UT, MT, and LT muscles increases as the shoulder abduction angle increases |
| Muscle Activation | Prone horizontal abduction (PHA) is an exercise for activating the MT and LT muscles |
| Muscle Contraction | The muscle belly is visible when maximal muscle contraction is induced during manual muscle testing (MMT) |
| Muscle Elongation | Shoulder horizontal abduction increases the elongation of the pectoralis minor muscle |
| Muscle Strengthening | Horizontal shoulder abduction strengthens the shoulder and upper back muscles, promoting good posture and preventing injuries |
| Muscle Stretch | Shoulder horizontal abduction stretches the pectoralis minor muscle, increasing its shear elastic modulus |
| Muscle Pathology | Deltoid pathologies include enthesitis, calcific tendinitis, myositis, infection, tumors, and chronic avulsion injury |
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What You'll Learn
The posterior deltoid muscle
The deltoid muscle is a large, triangular-shaped muscle that lies over the shoulder joint, giving it a rounded contour. It is divided into three distinct sections: anterior or clavicular, middle or acromial, and posterior or spinal. The posterior deltoid is primarily responsible for extension, external rotation, and horizontal abduction of the shoulder joint.
The posterior deltoid is a powerful muscle that plays a crucial role in various everyday activities and athletic movements. It is involved in actions such as putting on clothes, carrying shopping bags, washing hair, and playing sports like netball, swimming, and water polo.
During horizontal shoulder abduction, the arms are raised to the sides while maintaining a straight, level position. This movement specifically targets the posterior deltoid muscle, strengthening the shoulder and upper back muscles. It is important to keep the arms straight and at chest level, bringing them out to the sides while squeezing the shoulder blades together.
The posterior deltoid is also susceptible to injuries, especially with repetitive overhead activities or carrying heavy objects. Deltoid pathologies can lead to functional disfunction of the shoulder complex, and tears in the deltoid muscle may further compromise shoulder function. Therefore, it is essential to maintain proper form during exercises like horizontal shoulder abduction to avoid injuries and maintain shoulder health.
In summary, the posterior deltoid muscle is a critical muscle in the shoulder joint, responsible for various movements, including horizontal abduction. Strengthening and maintaining the health of this muscle is essential for overall shoulder function and stability.
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Pectoralis minor muscle
The pectoralis minor muscle is a superficial muscle on the anterior aspect of the chest or thoracic wall. It is located deep to the pectoralis major muscle, which almost completely covers it. The pectoralis minor muscle arises as three separate heads from the anterior surface of the third, fourth, and fifth ribs near the corresponding costal cartilages. The tendon of insertion may extend over the coracoid process to the greater tubercle.
The pectoralis minor muscle plays a role in respiration, elevating the ribs for deep inspiration when the pectoral girdle is fixed or elevated. When the ribs are immobilized, this muscle brings the scapula forward. It also works with the serratus anterior muscle to create a full range of movement for the scapula and can be used as an accessory muscle of respiration. Together, the pectoralis minor and serratus anterior muscles act in protraction of the scapula, moving it laterally and anteriorly against the rib cage. This movement is important in reaching the arm forward.
The medial and lateral pectoral nerves penetrate the pectoralis minor muscle to innervate it. The vascular supply to the pectoralis minor comes from several sources, including the thoracoacromial artery, superior thoracic artery, and lateral thoracic artery. The primary nerve supply to the pectoralis minor muscle comes via the medial pectoral nerve (C8, T1), a minor branch of the brachial plexus that arises from the cervical portion of the spinal cord.
The pectoralis minor muscle is clinically important and used as a surgical landmark due to the structures that lie below or deep to the muscle and its tendon. Running deep to the pectoralis minor muscle are the nerves and blood supply to the upper limb, including the posterior, lateral, and medial cords of the brachial plexus. The pectoralis minor is also used as a reference point for the three divisions of the axillary artery.
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Serratus anterior muscles
The serratus anterior (SA) is a fan-shaped muscle that originates on the superolateral surfaces of the first to eighth or ninth ribs at the lateral wall of the thorax. Its main part lies deep under the scapula and the pectoral muscles. It is easily palpable between the pectoralis major and latissimus dorsi muscles. In athletic bodies, the muscle may even be visible to the naked eye along the ribs underneath the axilla.
The serratus anterior is also known as the "boxer's muscle" as it is largely responsible for the protraction of the scapula, a movement that occurs when throwing a punch. It is the prime mover in both scapular protraction and scapular upward rotation. It is a key scapular stabiliser, keeping the shoulder blades against the ribcage when at rest and during movement. The lowest four digitations of the serratus anterior interdigitate with the fibres of the external oblique.
The serratus anterior is divided into three parts: the upper/superior, middle/intermedius, and lower/inferior. The upper part involves the first and second ribs attaching to the superior angle of the scapula. The middle part involves the second and third ribs attaching to the medial border of the scapula. The lower part involves the fourth to ninth ribs attaching to the medial border and inferior angle of the scapula. The lower part of the muscle is the most prominent and powerful.
Weakness of the serratus anterior leads to an altered line of pull of the rotator cuff muscle, which could increase the risk of subacromial impingement syndrome. The most common causes of serratus anterior muscle pain include tension, stress, and overuse. This pain may also result from serratus anterior myofascial pain syndrome (SAMPS), a rare myofascial pain syndrome.
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Shoulder abduction angles
The shoulder-abduction angle is often modified during scapular-retraction exercises, especially to produce lower upper trapezius (UT)/middle trapezius (MT) and UT/LT ratios. The shoulder-abduction angle is a crucial factor in determining the extent of joint dysfunction and monitoring treatment and rehabilitation progress.
During external rotation (ER) exercises, the preferred humeral position and shoulder angle vary depending on different body positions, which can affect the muscle activity patterns of the shoulder. For instance, lower trapezius muscle activity is higher during ER in a prone lying position compared to a standing position. Additionally, upper trapezius muscle activity decreases during ER at a 45-degree shoulder abduction angle compared to a 90-degree angle.
Research has shown that during prone horizontal abduction (PHA), the activity of the UT, MT, and LT muscles significantly increases as the shoulder abduction angle increases. At a 90-degree PHA, Moseley et al. reported one of the most optimal postures with high activity of both the MT and LT muscles.
Furthermore, during scapular-retraction exercises with elastic resistance, retraction at 0 degrees, 45 degrees, and 120 degrees can be preferable in early shoulder training or rehabilitation due to the relative activity of the UT and MT. Retraction at 90 degrees is the most effective exercise for activating all parts of the trapezius muscle.
In summary, the shoulder-abduction angle plays a significant role in shoulder muscle activity and rehabilitation. Different angles target specific muscles and can be utilised to restore muscle imbalances or prevent injuries.
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Scapular retraction
To perform scapular retraction exercises, individuals can start by standing or sitting tall with their arms at their sides. It is important to keep the shoulders relaxed and down, avoiding rounding the upper back or overextending the neck. The movement focuses on pulling the scapulars down and together, activating the middle back muscles, including the rhomboids and trapezius muscles.
One variation of scapular retraction involves using a resistance band or pull-up bar. With a resistance band, individuals can straighten their backs, lean back slightly, and pull the band toward their lower abdomen, just above the thighs. With a pull-up bar, individuals start from a full hang position and pull their scapulars down and together. These exercises can also be performed with the assistance of a physical therapist to ensure correct form.
The benefits of scapular retraction exercises extend beyond shoulder health. By targeting the muscles surrounding the shoulder blades, scapular retractions can improve posture, mitigate upper body injuries, and enhance respiratory capacity by expanding the chest region. Additionally, these exercises can serve as an effective warm-up routine, preparing the muscles for more rigorous upper-body training.
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Frequently asked questions
Horizontal abduction is an exercise that targets the shoulder and upper back muscles. It is performed by standing tall with your feet hip-width apart and holding both arms straight out in front of you with your palms facing up and elbows extended. The movement involves bringing your arms out to the sides while squeezing your shoulder blades together and then slowly returning to the starting position.
The primary muscles activated during horizontal abduction are the MT and LT muscles, with some involvement of the UT muscle. Additionally, the posterior deltoid muscle is also active during horizontal abduction.
Horizontal abduction exercises help strengthen the shoulder and upper back muscles, promoting good posture and reducing the risk of injuries during everyday activities such as lifting or reaching.
Yes, horizontal abduction can also be performed while seated on a chair, which is suitable for individuals with poor balance or unsteady feet. Additionally, the exercise can be modified by adjusting the angle of shoulder abduction, with common angles being 30 degrees, 60 degrees, 90 degrees, and 120 degrees.
It is important to maintain proper form during horizontal abduction exercises. Keep your arms straight and level, avoiding any bending at the elbows or allowing your arms to move up or down. Additionally, be mindful not to flare your ribs when squeezing your shoulder blades together.
