Deltoid muscle

Authors

Affiliations

Nate Yomogida, B.S., SPT

Doctor of Physical Therapy

B.S. in Kinesiology

Chloë Kerstein, B.S., SPT

Doctor of Physical Therapy

B.A. in Neuroscience

Figure 2: Muscles that position the Pectoral Girdle²

Figure 3: Muscles that move the humerus²

Reading list

Deltoid Muscle³
⁴
anterior deltoid MMT⁵
Middle delt MMT⁵
posterior deltoid MMT⁵

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Muscle	Origin	Insertion	Innervation	Action
Anterior deltoid	Lateral third of clavicle	Deltoid tuberosity of humerus	Axillary n. C5 - C6	GHJ: Flexion, IR, Adduction
Lateral deltoid	Acromion	Deltoid tuberosity of humerus	Axillary n. C5 - C6	GHJ: Abduction
Posterior deltoid	Scapular spine	Deltoid tuberosity of humerus	Axillary n. C5 - C6	GHJ: Extension, ER, Abduction

Overview

The deltoid is divided into 3 parts and 7 functional units.

Parts	Components
Anterior part	I & II
Lateral	III
Posterior	IV, V, VI, & VII

II, III, and IV lie lateral to the abduction axis and produce abduction⁶.

I, V, VI, and VII act as adductors. I and V are conditional and act as adductors when the upper limb hangs down vertically⁶. VI and VII always act as adductors⁶.

⁶
Component	a	Action
I
II	Lateral to abduction axis	Abduction
III	Lateral to abduction axis	Abduction
IV	Lateral to abduction axis	Abduction
V
VI		Adduction
VII		Adduction

Anterior head

Origin

Lateral 1/3 of clavicle⁷

Figure 4: Left Clavicle (superior view)¹

Figure 5: Left clavicle (inferior view)¹

Insertion

Humerus (deltoid tuberosity)⁷

Innervation

Axillary n. C5, C6⁷

Action

Flexion, internal rotation, adduction⁷

Lateral part

Origin

Acromion⁷

Insertion

Humerus (deltoid tuberosity)⁷

Innervation

Axillary n. C5, C6⁷

Action

Abduction⁷

Note

*Between 60 and 90 degrees of abduction, the clavicular and spinal parts assist the acromial part with abduction⁷

Posterior part

Origin

Scapular spine⁷ ### Insertion Humerus (deltoid tuberosity)⁷

Innervation

Axillary n. C5, C6⁷

Action

Extension, external rotation, adduction⁷

Note

*Between 60 and 90 degrees of abduction, the clavicular and spinal parts assist the acromial part with abduction⁷

Abduction Activation

The deltoid is active at the start of abduction and achieve full abduction⁶. The deltoid’s peak efficiency occurs at 90°⁶. It can generate up to 8.2x the weight of the upper limb⁶.

Pure abduction

Pure abduction occurs in the frontal plane.

Component III of lateral deltoid recruits first
IV and V of posterior deltoid recruit immediately after⁶.
Component II (anterior delt) recruits after the first 20-30°⁶.

Scapular plane abduction

Scapular plane exists between the sagittal and frontal planes. 30° from the frontal plane⁶.

II (anterior deltoid) and III (lateral deltoid) are recruited first⁶.
IV and V (posterior deltoid) and I (Anterior deltoid) are recruited progressively later⁶.

External rotation into abduction

II (anterior deltoid) contracts at the start

Note

IV and V (Posterior deltoid) do not contract at all during this movement⁶.

IR to abduction

“recruitment order reverses”⁶.

Clinical Relevance

As the GHJ becomes more unstable, the deltoid muscle takes on more of a stabilizing role⁸

Strength Testing

Palpation

Dysfunction

Strain-Counterstrain

Strain counterstrain for the “bursa” or “deltoid muscle”⁹.

“BURSA (Deltoid Muscle) Location of Tender Point: Flex or abduct the arm to 90° to allow palpation beneath the acromion process by shortening and relaxing the deltoid muscle. Anatomical Correlation: Any part of the deltoid muscle. Direction to Press on Tender Point: Press from superior to inferior with the arm in the stated position above. Treatment Position(s): With patient supine or seated, the shoulder is flexed or abducted 90° to 120°. Rotation varies from slightly internal to slightly external depending on the part of the deltoid muscle that is involved. Frequency of Occurrence: Uncommon to rare. Many muscles refer pain to the area of the deltoid muscle and most of the time it is not the deltoid causing the pain. Wag Clinical Correlation(s): Pain in the anterior, lateral, or posterior shoulder over the deltoid depending on which part of the muscle is involved. Associated Pain Referral Pattern: Pain in the upper arm. Alternate Names/Nomenclatures: None. Explanatory Notes: None.”⁹

References

Gray H. Anatomy of the Human Body. 20th ed. (Lewis WH, ed.). Lea & Febiger; 1918. https://www.bartleby.com/107/

Betts JG, Blaker W. Anatomy and Physiology. 2nd ed. OpenStax; 2022. https://openstax.org/details/books/anatomy-and-physiology-2e/?Book%20details

Donnelly JM, Simons DG, eds. Travell, Simons & Simons’ Myofascial Pain and Dysfunction: The Trigger Point Manual. Third edition. Wolters Kluwer Health; 2019.

Neumann DA, Kelly ER, Kiefer CL, Martens K, Grosz CM. Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation. 3rd ed. Elsevier; 2017.

Weinstock D. NeuroKinetic Therapy: An Innovative Approach to Manual Muscle Testing. North Atlantic Books; 2010.

Jones B. B Project Foundations. b Project; 2025.

Gilroy AM, MacPherson BR, Wikenheiser JC, Voll MM, Wesker K, Schünke M, eds. Atlas of Anatomy. 4th ed. Thieme; 2020.

Kido T, Itoi E, Lee SB, Neale PG, An KN. Dynamic stabilizing function of the deltoid muscle in shoulders with anterior instability. The American Journal of Sports Medicine. 2003;31(3):399-403. doi:10.1177/03635465030310031201

Myers HL, Devine WH, Fossum C, et al. Compendium Edition: Clinical Application of Counterstrain. Compendium ed. Osteopathic Press; 2012.

Citation

For attribution, please cite this work as:

Yomogida N, Kerstein C. Deltoid muscle. https://yomokerst.com/The Archive/Anatomy/Skeletal Muscles/Upper Limb Muscles/Intrinsic Shoulder Muscles/deltoid_muscle.html