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The deltoid muscle is a large, triangular-shaped muscle that forms the shoulder's rounded contour. It is a common site for intramuscular injections, including vaccinations. The deltoid muscle helps to lift the arm to the front, side, and back, and is activated when carrying heavy weights. It is also responsible for abducting the arm and stabilizing the shoulder joint. The deltoid muscle is made up of three distinct parts: the anterior, lateral, and posterior. Each of these parts has specific functions and attachments within the shoulder, allowing for a wide range of arm movements.
| Characteristics | Values |
|---|---|
| Description | Large, triangular-shaped muscle |
| Location | Shoulder, covering the front, side, and back of the joint |
| Function | Elevation of the arm, abduction of the shoulder, stabilisation of the humeral head, assists in forward elevation |
| Composition | Three distinct sets of muscle fibres: anterior or clavicular, middle or acromial, and posterior or spinal |
| Blood Supply | Various branches of the axillary artery, including the thoracoacromial artery, circumflex humeral arteries, and the profunda brachii artery |
| Innervation | Axillary nerve |
| Average Mass | 192 grams, ranging from 84 grams to 366 grams |
| Pathologies | Tears, fatty atrophy, enthesopathy, enthesitis, calcific tendinitis, myositis, infection, tumours, chronic avulsion injury |
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What You'll Learn
Deltoid muscles help lift and move arms in different directions
The deltoid muscle is a large, triangular-shaped muscle that covers the top of the shoulder, giving it its rounded contour. It is comprised of three distinct parts: the anterior or clavicular, the lateral or acromial, and the posterior or spinal. These parts attach to different regions of the shoulder, with the anterior connecting to the clavicle, the lateral to the acromion, and the posterior to the scapula.
The deltoid muscle helps lift and move the arms in different directions. The anterior deltoids, or front delts, help move the arm forward, such as when reaching for an object on a shelf. The lateral deltoids, or side delts, assist in moving the arm out to the side, as well as up and down. They are engaged when performing activities like jumping jacks.
The deltoid muscle is the prime mover of arm abduction along the frontal plane when all its fibres contract simultaneously. It acts as the principal abductor of the arm at the glenohumeral joint, but it can only do so when the arm is already abducted beyond fifteen degrees. This initial part of abduction is facilitated by the supraspinatus muscle. The deltoid also plays a role in stabilising the glenohumeral joint, preventing dislocation.
Additionally, the deltoid muscle undergoes eccentric contraction during the lowering or adduction of the arm, allowing for controlled movement. The anterior deltoid contracts to produce extension and lateral rotation of the arm, while contraction of the posterior deltoid causes the arm to flex and medially rotate. These fibres also work together during walking or running motions, with the anterior fibres assisting the pectoralis major in arm flexion.
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They are a common site for intramuscular injections
The deltoid muscle is a large, triangular-shaped muscle that forms the rounded contour of the human shoulder. It is a superficial muscle, which means it is close to the surface of the skin. Due to its superficial nature, it is a common site for intramuscular injections. Its ease of access makes it a convenient site for administering vaccines or medications.
The deltoid muscle is divided into three parts: the anterior, lateral, and posterior. These different parts of the deltoid have distinct functions and attachments within the shoulder region. The anterior deltoid, often referred to as the front delt, helps move the arm forward. It is used when reaching for an object on a shelf, for example. The lateral deltoid, or side delt, assists in moving the arm out to the side, as well as up and down. This lateral deltoid is engaged when performing jumping jacks. The posterior deltoid, also known as the rear delt, contributes to the extension, external rotation, and horizontal abduction of the arm.
The deltoid muscle plays a crucial role in shoulder abduction, allowing us to lift our arms. Additionally, it has smaller roles in flexion and extension movements of the arm. When all the parts of the deltoid contract simultaneously, it results in the abduction of the shoulder, provided the arm is already held at a certain angle of abduction. This muscle also helps prevent dislocation of the glenohumeral joint, especially when carrying heavy weights.
The deltoid muscle is susceptible to various pathologies, including tears, tendinitis, myositis, and chronic avulsion injuries. These issues can lead to functional dysfunctions of the shoulder complex. Therefore, it is essential to properly assess the function of the deltoid muscle to determine any muscular or nervous injuries accurately.
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They are superficial muscles, close to the skin's surface
The deltoid muscle is a large, triangular-shaped muscle that forms the rounded contour of the human shoulder. It is also known as the 'common shoulder muscle'. The deltoid muscle is superficial, meaning it is close to the skin's surface. The deltoid muscle is responsible for giving the shoulder its shape and is one of the six intrinsic muscles of the shoulder. The other five intrinsic muscles include the teres major and the four rotator cuff muscles.
The deltoid muscle is composed 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 fibres converge towards their insertion on the deltoid tuberosity of the humerus. The anterior fibres assist the pectoralis major in flexing the shoulder and work with the subscapularis, pecs, and lats to internally (medially) rotate the humerus.
The deltoid muscle is a powerful muscle that is used in many everyday activities, such as putting clothes on a line, carrying shopping bags, or washing hair. It is also used in athletic activities such as netball, swimming, and water polo. The deltoid muscle is the prime mover of arm abduction along the frontal plane when all its fibres contract simultaneously. The arm must be medially rotated for the deltoid to have its maximum effect.
The deltoid muscle can be easily observed and palpated due to its superficial nature. It is important to properly test the function of the deltoid muscle to determine muscular or nervous injury. Deltoid pain can affect individuals who perform repetitive overhead activities, such as swimmers, pitchers, or house painters.
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Deltoid muscles are one of the main abductors of the shoulder
The deltoid muscle is a large, triangular-shaped muscle that forms the rounded contour of the human shoulder. It is also known as the 'common shoulder muscle'. The deltoid is a superficial muscle, meaning it lies close to the surface of the skin. It is one of the six intrinsic muscles of the shoulder and is responsible for giving the shoulder its shape. The deltoid muscle is one of the main abductors of the shoulder, which means it helps lift the arm when reaching for objects or brushing hair. It is activated when carrying heavy weights, like a suitcase or grocery bags, to prevent dislocation of the glenohumeral joint.
The deltoid muscle 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). The deltoid's fibres are pennate muscle, and they converge towards their insertion on the deltoid tuberosity of the humerus. The base of the deltoids connects to the upper part of the scapula (shoulder blade) and the side of the clavicle (collarbone). The point of the deltoids attaches to the side of the humerus, which is the arm bone between the shoulder and elbow.
The deltoid muscle is the prime mover of arm abduction along the frontal plane when all its fibres contract simultaneously. The arm must be medially rotated for the deltoid to have maximum effect. The anterior deltoid contracts to produce extension and lateral rotation of the arm, while the lateral part of the deltoid contracts independently to cause arm abduction. The contraction of the posterior deltoid makes the arm flex and medially rotate. The anterior and posterior deltoid muscle fibres are used to swing the arms when walking.
The deltoid muscle is responsible for elevating the arm in the scapular plane, and its contraction in doing this also elevates the humeral head. The deltoid also undergoes eccentric contraction when the arm is being lowered or adducted, allowing for controlled adduction. The deltoid compensates for the loss of strength in the rotator cuff and can undergo tears, which may further jeopardise shoulder function. Deltoid pain can affect individuals who perform repetitive overhead activities, such as swimmers, pitchers, or house painters.
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They are stabilisers of the shoulder joint
The deltoid muscle is a large triangular muscle that forms the shoulder's rounded contour. It is comprised of three distinct parts: the anterior or clavicular, the middle or acromial, and the posterior or spinal. The deltoid is a key shoulder stabilizer, preventing inferior glenohumeral joint displacement while the arm is completely adducted and bearing a heavy load.
The deltoid muscle helps to stabilize the glenohumeral joint, which is the ball-and-socket joint that connects the arm to the trunk of the body. The deltoid prevents subluxation/dislocation of the shoulder joint, especially when carrying heavy weights or reaching for objects. It is activated when carrying heavy objects to prevent the inferior displacement of the glenohumeral joint.
The deltoid muscle is the prime mover of arm abduction along the frontal plane when all its fibres contract simultaneously. The arm must be medially rotated for the deltoid to have its maximum effect. The anterior deltoid works with the pectoralis major to flex the arm when walking, while the posterior deltoid works with the latissimus dorsi to extend the arm during ambulation. The anterior fibres assist the pectoralis major to flex the shoulder, while the posterior fibres assist the latissimus dorsi to extend the shoulder.
The deltoid muscle is responsible for elevating the arm in the scapular plane, and its contraction in doing this also elevates the humeral head. The deltoid helps to move the arm in different directions, including forward, side, and back. The anterior deltoids help move the arm forward, the lateral deltoids help move the arm out to the side as well as up and down, and the posterior deltoids help with extension and external rotation of the arm.
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Frequently asked questions
The deltoid muscle is a large, triangular-shaped muscle that covers the front, side, and back of the shoulder. It is also known as the 'common shoulder muscle'.
The deltoid muscle helps lift the arm to the front, side, and back, and also assists in moving the arm in different directions. It is one of the main abductors of the shoulder, helping to lift the arm when reaching for objects or brushing hair.
The deltoid muscle is anatomically divided into three parts: the anterior or clavicular (front deltoid), the lateral or acromial (side deltoid), and the posterior or spinal (rear deltoid). The anterior deltoid helps move the arm forward, the lateral deltoid helps with moving the arm out to the side and up and down, and the posterior deltoid works with the latissimus dorsi to extend the arm during walking.
Deltoid muscle pain can affect individuals who perform repetitive overhead activities, such as swimmers, pitchers, and painters. Common abnormalities affecting the deltoid include tears, fatty atrophy, and enthesopathy. Tears are often associated with traumatic shoulder dislocations or massive rotator cuff tears.
