Teres Major: Origin, Insertion, Nerve, Action & "Lat's Little Helper"

The Teres Major is a thick, rounded muscle located on the posterior aspect of the scapula. Although it sits right next to the rotator cuff muscles (specifically Teres Minor), it is not a rotator cuff muscle itself. Instead, it acts as a synergist to the Latissimus Dorsi.

[Image of Teres Major muscle anatomy]

Quick Anatomy Snapshot

Origin (Proximal)	Posterior surface of the Inferior Angle of the Scapula.
Insertion (Distal)	Medial Lip of the Intertubercular (Bicipital) Groove of the Humerus.
Nerve Supply	Lower Subscapular Nerve (C5, C6, C7).
Blood Supply	Subscapular and Circumflex Scapular Arteries.
Primary Actions	Internal Rotation: Turns the arm inward. Adduction: Pulls the arm toward the body. Extension: Pulls the arm backward.

Deep Dive: The "Little Helper"

To understand Teres Major, think of it as the "Little Brother" of the Latissimus Dorsi. It shares the exact same actions but is smaller.

1. "The Lady Between Two Majors"

This mnemonic describes the attachments at the Bicipital Groove of the humerus:
• Pectoralis Major: Lateral Lip.
• Teres Major: Medial Lip.
• Latissimus Dorsi ("The Lady"): Floor (between the two "Majors").

2. The Anatomical Spaces

The Teres Major forms the inferior border of two important spaces:
• Quadrangular Space: transmits Axillary Nerve & Posterior Circumflex Humeral Artery.
• Triangular Space: transmits Circumflex Scapular Artery.
The Teres Minor forms the superior border of these spaces.

Physio Corner: Clinical Relevance

💪 Functional Fact: The Teres Major is crucial for movements like reaching into your back pocket (Internal Rotation + Extension) or chopping wood. It needs to be stabilized by the Rhomboids to be effective.

Palpation

Ask the patient to place their hand on their posterior iliac crest (back of hip). This position relaxes the Deltoid. Palpate the lateral border of the scapula near the bottom. The fleshy mass you feel is the Teres Major. If you ask the patient to push their elbow backward against resistance, it will firm up.

⚠️ Clinical Pathology: Tightness vs. Weakness
Because Teres Major is an internal rotator, tightness here contributes to limited external rotation (e.g., difficulty combing hair). It is often implicated in "Upper Crossed Syndrome" along with the Lats and Pecs.

Manual Muscle Testing (MMT)

Testing the Teres Major specifically is difficult because the Lats always want to help.

Testing Tip: To differentiate from the Posterior Deltoid (which also extends), ensure the patient is Adducting and Internally Rotating the arm (hand on back hip position).

Step-by-Step Procedure (Oxford Scale)

Grade	Patient Action & Resistance
Grade 3, 4, 5 (Against Gravity)	Position: Prone. Hand resting on the posterior iliac crest (palm up/out). Action: Patient lifts the elbow towards the ceiling (Extension + Adduction). Resistance: Applied at the distal humerus (above elbow), pushing down and out. Grade 3: Clears range against gravity. Grade 4/5: Holds against resistance.
Grade 2 (Gravity Eliminated)	Position: Sitting or Side-lying. Arm supported. Action: Patient moves arm into extension and adduction. Result: Full range of motion.
Grade 0, 1 (Palpation)	Action: Palpate lateral border of scapula inferiorly. Cue: "Try to bring your elbow back." Grade 1: Contraction felt. Grade 0: No activity.

Frequently Asked Questions

Is Teres Major part of the Rotator Cuff?

No. The rotator cuff muscles (Supraspinatus, Infraspinatus, Teres Minor, Subscapularis) attach to the tubercles and stabilize the head. Teres Major attaches to the shaft and is a prime mover.

What is its relationship to the Triceps?

The Teres Major passes anterior to the Long Head of the Triceps Brachii. The Teres Minor passes posterior to it. This anatomic relationship is key for identifying the muscles in dissection.

Does it abduct the arm?

No. It is a strong Adductor. It pulls the arm down and in.

Test Your Knowledge: Teres Major Quiz

1. Where does Teres Major insert?

2. Which nerve supplies Teres Major?

3. What is the primary action of Teres Major?

4. Which muscle is the "Big Brother" to Teres Major?

5. Where does Teres Major originate?

6. The Teres Major forms the inferior border of the:

7. Which movement stretches the Teres Major?

8. Does the Teres Major attach to the Glenoid Labrum?

9. The Long Head of the Triceps runs ________ to the Teres Major.

10. True or False: Teres Major is a Rotator Cuff muscle.

References

• Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2018). Clinically Oriented Anatomy. 8th ed. Philadelphia: Wolters Kluwer.
• Standring, S. (2016). Gray's Anatomy: The Anatomical Basis of Clinical Practice. 41st ed. Elsevier.
• Kendall, F. P. (2005). Muscles: Testing and Function, with Posture and Pain. 5th ed. Lippincott Williams & Wilkins.