Maximus Gage
The deltoid muscle is a large, triangular-shaped muscle that covers the shoulder joint and gives it its rounded shape. It is a powerful muscle that is used in many everyday activities, such as getting dressed or carrying shopping bags, as well as athletic activities like swimming and netball. Deltoid muscles can be tested through manual muscle testing (MMT), which assesses muscle/tendon strength. This involves positioning the patient in a specific way to target the deltoid muscle and applying external force to test its strength. The examiner will then provide a numerical grade to document the patient's muscle strength.
| Characteristics | Values |
|---|---|
| Deltoid Muscle Description | A large triangular-shaped muscle that lies over the glenohumeral joint and gives the shoulder its rounded contour |
| Deltoid Muscle Composition | Three distinct portions: anterior or clavicular, middle or acromial, and posterior or spinal |
| Deltoid Muscle Function | Mainly acts as an abductor of the shoulder and stabiliser of the humeral head, as well as assists in forward elevation |
| Deltoid Muscle Testing | Manual Muscle Testing (MMT) is used to assess muscle/tendon strength and provide a baseline measurement for evaluation |
| Deltoid Muscle Testing Position | Patient lying supine on a table with knees in a flexed position, therapist standing behind the patient |
| Deltoid Muscle Testing Procedure | Gradual pressure is applied until there is a "break" in position or the examiner determines the test is complete |
| Deltoid Muscle Strength Grading | Fair (3+), Fair (3), Fair (3-), Poor (2+), Poor (2), Poor (2-), Trace (1), Zero (0) based on ability to hold against gravity and resist pressure |
| Deltoid Muscle Strengthening Exercises | Wall push-off, dumbbell weight arm raises, resistance band exercises, shoulder diagonal PNF with a band, compound exercises, high side plank walking |
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What You'll Learn
Manual muscle testing: shoulder flexion
Manual muscle tests (MMT) are an important way to assess the strength of muscles and tendons. They are used to establish a baseline measurement that can be referred back to when assessing a patient's response to intervention. MMTs are also used to determine the muscle responsible for a movement deficit.
Shoulder flexion occurs in the sagittal plane and has a normal range of motion (ROM) of 0-180 degrees. The glenohumeral joint, of the shoulder girdle, is associated with shoulder flexion osteokinematics. To initiate shoulder flexion, the coracobrachialis muscle must posteriorly roll the humeral head on the glenoid fossa. The coracobrachialis, anterior deltoid, and biceps brachii continue to promote the posterior roll until the end-of-range.
To test shoulder flexion, the patient assumes a hook-lying position on a table, lying supine with their knees in a flexed position and feet flat on the ground. The examiner then passively moves the affected shoulder into flexion and slight external rotation, the elbow into full flexion, and the forearm into full supination. This positioning decreases the assistance of the biceps brachii. The examiner then asks the patient to perform the actions without assistance, ensuring their achievement of full ROM. If no pain is present, the examiner resets the patient to the starting test position and applies gradual resistance against the anteromedial surface of the distal humerus, in the direction of shoulder extension. The patient does their best to resist the external force of shoulder flexion and adduction until there is a "break" in position or the examiner determines the test is complete.
The examiner can then assign a grade to the patient's performance, which demonstrates the patient's muscle/tendon strength. A grade of "fair" (3+) means the patient was able to hold against gravity and resist minimal pressure before muscle failure, while a grade of "poor" (2+) means the patient was unable to hold against gravity but achieved partial ROM against gravity.
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Deltoid strengthening exercises
The deltoid muscle is a crucial part of the shoulder complex, providing strength and stability to the shoulder joint. It is divided into three parts, each responsible for a different type of movement: the anterior (front) deltoid, which enables shoulder flexion; the middle deltoid, which is in charge of abduction; and the posterior (back) deltoid, which facilitates shoulder extension.
Overhead Press with Dumbbells:
- Stand with your feet hip-width apart and hold a dumbbell in each hand.
- Press the weights up above your head until your arms are fully extended.
- Slowly lower the weights back down to the starting position and repeat.
- Aim for 10-15 repetitions in three sets.
Lateral Raises with Dumbbells:
- Stand with your feet slightly wider than shoulder-width apart, with one hand resting on an upright bench.
- Hold a dumbbell in front of you, hinging at the hips.
- Laterally raise the dumbbell while slightly bending your elbow, and simultaneously retract your shoulder blade.
- Slowly lower the dumbbell back down and repeat for 10-12 reps, completing three sets.
Shoulder-Level Raises with Dumbbells:
- Stand with your feet hip-width apart and hold a dumbbell in each hand.
- Lift your arms to the side until they reach shoulder level.
- Slowly lower your arms back down to your sides and repeat.
- This exercise specifically targets the deltoid muscle and rotator cuff.
- Aim for 10-12 reps in three sets.
These exercises will help strengthen the deltoid muscle, improving shoulder stability, posture, and overall shoulder joint health.
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Shoulder osteokinematics and arthrokinematics
The shoulder is a complex joint with a wide range of motion, and its biomechanics are influenced by the movement of the scapula along the thoracic cage. Shoulder osteokinematics and arthrokinematics are essential to understanding the shoulder's movement and any resulting injuries.
Osteokinematics refers to the movement of the bones, and in the context of the shoulder, it involves flexion/extension, abduction/adduction, and medial/lateral rotation. The shoulder's osteokinematics are closely related to the fascial system, which impacts multi-joint movements and force transfer across the system. A very dense, hypertonic latissimus dorsi, for example, can cause problems at the shoulder by depressing the entire shoulder girdle.
Arthrokinematics, on the other hand, refers to the movement of joint surfaces. In the shoulder, this includes the various directional glides of the humeral head within the glenoid fossa. The natural arthrokinematics of the GH joint during an open-chain movement support these glides, and abnormal glenohumeral translations have been linked to pathological shoulders and shoulder pain.
The success of a coordinated movement of the humeral head with normalized arthrokinematics depends on the harmonious co-contraction of the RC tendons. The RC tendons have been shown to compress the humeral head within the glenoid fossa during movements, and the supraspinatus muscle initiates the abduction movement of the arm by pulling the humeral head towards the glenoid cavity, creating a fulcrum for movement.
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Signs of deltoid weakness
The deltoid muscle is a large muscle that gives the shoulder its range of motion and is responsible for lifting the arm. The deltoid muscle is susceptible to injury and pain due to its location and function. Deltoid muscle weakness can be identified through specific signs and symptoms.
One sign of deltoid muscle weakness is a noticeable loss of muscle tissue and thinning of the muscle, also known as muscle atrophy. This can be visually observed, and the affected individual may notice a decrease in the size or definition of their deltoid muscle. Additionally, individuals with deltoid muscle weakness may experience difficulty in lifting their arm or performing shoulder movements. They might feel pain or tenderness at the front, side, or back of the shoulder, especially when attempting to lift the arm. The severity of the strain can vary from mild tightness to severe, restricting pain.
In more serious cases of deltoid muscle weakness, individuals may experience severe pain, swelling, and the formation of a muscle bulge or gap. The pain can be so intense that it severely limits or completely restricts the movement of the arm. This level of discomfort can significantly impact an individual's ability to perform daily tasks and routine activities.
To confirm deltoid muscle weakness, specific tests can be performed, such as electromyography (EMG) and nerve conduction tests. However, these tests may not show abnormalities right after an injury, and it is recommended to conduct them several weeks after the onset of symptoms. Early diagnosis and treatment are crucial for axillary nerve dysfunction, which can lead to a loss of movement or sensation in the shoulder. Physical therapy, job changes, and muscle retraining can help maintain muscle strength and aid in recovery.
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Deltoid extension and external rotation
The deltoid muscle is a large, triangular-shaped muscle that lies over the glenohumeral joint and gives the shoulder its rounded contour. It is made up of three distinct sections: anterior or clavicular, middle or acromial, and posterior or spinal. The deltoid muscle helps lift the arm to the front, side, and back. It also compensates for the loss of strength in the rotator cuff.
To test the deltoid muscle, the patient should be sitting or supine, with the examiner standing behind them and holding the patient's testing shoulder. The therapist will place one hand on the patient's forearm and use the other hand to push the shoulder anteriorly from the posterior, lengthening the muscle. This is known as deltoid extension and external rotation. The anterior deltoid's primary function is flexion, internal rotation, and horizontal adduction. To stretch this muscle, reverse the action by performing extension, external rotation, and horizontal abduction of the shoulder, without letting the torso rotate.
The drop-arm test can be used to evaluate a possible rotator cuff tear. This test involves passively abducting the patient's shoulder and observing as the patient slowly lowers their arm to the waist. If the patient has a rotator cuff tear or supraspinatus dysfunction, their arm will drop to the side. The patient may be able to lower their arm to 90 degrees, but they will be unable to continue the movement to the waist.
Posterior instability of the shoulder can be assessed by pushing posteriorly on the humeral head with the patient's arm in 90 degrees of abduction and the elbow in 90 degrees of flexion. Glenoid labral tears are assessed with the patient supine, and their arm is rotated and loaded from extension through to forward flexion. A "clunk" or clicking sensation may indicate a labral tear.
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Frequently asked questions
The deltoid muscle is a large, triangular-shaped muscle that covers the shoulder joint and gives it its rounded shape. It is made up of three sections: anterior or clavicular, middle or acromial, and posterior or spinal.
The deltoid muscle is a powerful muscle that acts as an abductor of the shoulder, stabilises the head of the humerus (upper arm bone), and assists in forward elevation. It is used in everyday activities such as putting on clothes, carrying shopping bags, and washing hair, as well as athletic activities like swimming and netball.
One way to test the strength of the deltoid muscle is through Manual Muscle Testing (MMT). This involves specific positioning and resistance to assess the muscle's strength and range of motion. For example, one test for the anterior deltoid is to have the patient lying on their back with their knees bent, and then resisting the external force of shoulder flexion and adduction.
During an MMT, the patient's ability to resist external forces and maintain their position is graded. If the patient exhibits signs of weakness, such as difficulty with shoulder flexion and internal rotation, it may indicate a weak deltoid muscle. However, further tests may be needed to isolate and confirm deltoid weakness.
Yes, there are several exercises that can help strengthen the deltoid muscle. These include:
- Standing with your back and elbow straight against a wall, and gently pushing your arm against the wall as hard as comfortably possible.
- Using dumbbells or resistance bands to perform forward, lateral, and posterior arm raises.
- Compound exercises such as forward arm raises with squats or high side plank walking.
