The deltoid muscle is not strictly a push or a pull muscle; it is a complex muscle group that participates in both types of movements depending on which of its three distinct sections is engaged. This muscle covers the shoulder joint and is responsible for nearly all arm movements. Understanding its dual role requires defining “push” and “pull” within resistance training.
Defining Push and Pull Movements
In strength training, “push” and “pull” categorize exercises based on the direction of force relative to the body. A push movement involves exerting force to move resistance away from the body’s core. This action primarily engages muscle groups on the front of the body, such as the chest, anterior shoulders, and triceps.
A pull movement is characterized by drawing resistance toward the body. These movements heavily recruit muscles on the back of the torso, including the latissimus dorsi, rhomboids, and biceps. This distinction helps frame how different sections of the deltoid contribute to upper body movement.
Anatomy and Function of the Deltoid Heads
The deltoid is comprised of three separate heads, each with a unique origin and primary function, allowing the shoulder to move in multiple planes.
The Anterior Deltoid is located at the front of the shoulder and originates from the clavicle. It is responsible for shoulder flexion, which is the action of lifting the arm forward.
The Medial Deltoid (side head) originates from the acromion process of the scapula. It is the main driver of shoulder abduction, or lifting the arm directly out to the side.
The Posterior Deltoid is situated on the back of the shoulder and originates from the spine of the scapula. Its primary movements are shoulder extension (moving the arm backward) and horizontal abduction.
Deltoid Involvement in Push Exercises
The push component of the deltoid is primarily driven by the Anterior Deltoid head due to its role in shoulder flexion. This front section is heavily recruited during exercises that press weight away from the body, such as the overhead press or the incline bench press.
During these movements, the anterior fibers work alongside the chest and triceps to elevate the arm. The Medial Deltoid also plays a significant role in pushing exercises, particularly those performed overhead.
It assists in the final stages of a shoulder press by helping to abduct the arm as it moves upward, contributing to shoulder joint stability under load. Isolation movements like lateral raises are also classified as a push, as the weight is moved away from the body’s center.
Deltoid Involvement in Pull Exercises
The pull function of the deltoid is managed by the Posterior Deltoid head. This rear section is responsible for moving the arm backward and horizontally away from the body, directly contributing to pulling motions.
It acts as a major stabilizer for the shoulder joint during exercises that recruit the larger back muscles. The posterior deltoid is highly active in pulling movements like bent-over rows, where it assists the upper back in retracting the shoulder blades.
Isolation exercises such as reverse flyes and face pulls specifically target the posterior deltoid, emphasizing its pull function to move the arm against resistance toward the body. Training this head is important for counteracting the forward pull of the stronger anterior muscles.