Upper Arm Muscles: Anatomy, Functions, and Training Implications

What are the names of the muscles in the upper arm?

The upper arm, or brachium, houses a distinct group of muscles primarily responsible for movement at the elbow and shoulder joints. These muscles are divided into two main compartments: the anterior (flexor) compartment and the posterior (extensor) compartment.

Understanding the Upper Arm Anatomy

The human upper arm is a complex region, anatomically defined as the segment between the shoulder and the elbow joints. Its muscular architecture is elegantly designed to facilitate a wide range of movements, from powerful lifting to fine motor control. For clarity, the muscles are typically categorized based on their primary function and anatomical location into two distinct compartments, separated by intermuscular septa that connect to the humerus (upper arm bone).

Muscles of the Anterior (Flexor) Compartment

The anterior compartment muscles are primarily responsible for flexing the elbow joint and, to a lesser extent, assisting with shoulder movements. They are innervated by the musculocutaneous nerve.

• Biceps Brachii:

  • Description: This is the most superficial and well-known muscle of the anterior compartment, giving the upper arm its characteristic bulge. Its name, "biceps," signifies its two heads of origin.
  • Heads:
    • Long Head: Originates from the supraglenoid tubercle of the scapula (shoulder blade), passing over the head of the humerus.
    • Short Head: Originates from the coracoid process of the scapula.
  • Insertion: Both heads merge to insert via a common tendon onto the radial tuberosity of the radius (forearm bone) and the bicipital aponeurosis into the deep fascia of the forearm.
  • Primary Actions: Powerful supination of the forearm (turning the palm upwards) and flexion of the elbow joint. It also assists in shoulder flexion.
  • Functional Note: While often perceived as the primary elbow flexor, its efficiency in this role is significantly enhanced when the forearm is supinated.

• Brachialis:

  • Description: Lying deep to the biceps brachii, the brachialis muscle is the true workhorse of elbow flexion.
  • Origin: Anterior surface of the humerus.
  • Insertion: Coronoid process and tuberosity of the ulna (forearm bone).
  • Primary Actions: Pure elbow flexion, regardless of forearm pronation or supination. It is active in all forms of elbow flexion.
  • Functional Note: Its direct attachment to the ulna, which does not rotate, makes it an exceptionally stable and consistent elbow flexor.

• Coracobrachialis:

  • Description: The smallest of the anterior compartment muscles, located deep to the short head of the biceps.
  • Origin: Coracoid process of the scapula.
  • Insertion: Medial surface of the humerus, midway down its shaft.
  • Primary Actions: Flexion and adduction of the arm at the shoulder joint. It also helps stabilize the shoulder joint.
  • Functional Note: Often considered a synergist to other shoulder movers, its primary role is in bringing the arm forward and towards the body's midline.

Muscles of the Posterior (Extensor) Compartment

The posterior compartment houses the primary muscle responsible for extending the elbow joint. It is innervated by the radial nerve.

• Triceps Brachii:

  • Description: The sole muscle of the posterior compartment, aptly named "triceps" for its three heads of origin. It forms the bulk of the posterior upper arm.
  • Heads:
    • Long Head: Originates from the infraglenoid tubercle of the scapula. This head crosses both the shoulder and elbow joints.
    • Lateral Head: Originates from the posterior surface of the humerus, superior to the radial groove.
    • Medial Head: Originates from the posterior surface of the humerus, inferior to the radial groove. This head is largely covered by the long and lateral heads.
  • Insertion: All three heads converge into a common tendon that inserts onto the olecranon process of the ulna.
  • Primary Actions: Powerful extension of the elbow joint. The long head also assists in adduction and extension of the arm at the shoulder joint.
  • Functional Note: Essential for pushing movements, throwing, and stabilizing the elbow during many activities.

• Anconeus:

  • Description: While technically located at the posterior aspect of the elbow joint and often considered part of the forearm musculature due to its small size and location, the anconeus is functionally associated with the triceps brachii.
  • Origin: Lateral epicondyle of the humerus.
  • Insertion: Lateral surface of the olecranon and posterior surface of the ulna.
  • Primary Actions: Assists the triceps in elbow extension and helps stabilize the elbow joint during pronation and supination. It also pulls the synovial membrane out of the way during extension to prevent pinching.

Functional Significance and Training Implications

Understanding the specific roles of these upper arm muscles is crucial for effective strength training and rehabilitation. For instance:

• Biceps: Targeted by exercises like bicep curls (dumbbell, barbell, hammer curls) and chin-ups. Varying grip (supinated, neutral, pronated) and elbow position can emphasize different heads or synergistic muscles.
• Brachialis: Engaged heavily in all elbow flexion exercises, particularly when the forearm is pronated (e.g., reverse curls), as the biceps' supination advantage is reduced.
• Triceps: Essential for pushing movements such as overhead presses, bench presses, push-ups, and various triceps extensions (e.g., skullcrushers, cable pushdowns).

Importance of Balanced Development

For optimal strength, functional performance, and injury prevention, it is vital to develop all upper arm muscles proportionally. An overemphasis on the biceps without adequate triceps training can lead to muscular imbalances, potentially affecting posture, joint stability, and increasing the risk of elbow or shoulder injuries. A well-rounded program will include exercises that target both the anterior (flexor) and posterior (extensor) compartments of the upper arm.

Conclusion

The muscles of the upper arm—the biceps brachii, brachialis, coracobrachialis in the anterior compartment, and the triceps brachii (with assistance from the anconeus) in the posterior compartment—are fundamental to the vast array of movements performed by the arm. A detailed understanding of their anatomy, origins, insertions, and actions provides a robust foundation for anyone seeking to optimize their physical performance, prevent injury, or deepen their knowledge of human kinesiology.