Upper Arm Muscles: Biceps, Triceps, Brachialis, and Coracobrachialis

What Muscle is in Shoulder to Elbow?

The region between the shoulder and the elbow, known as the brachium or upper arm, primarily houses four key muscles: the Biceps Brachii, Brachialis, Coracobrachialis, and Triceps Brachii, each playing distinct roles in arm movement and function.

The Anatomy of the Upper Arm: A Comprehensive Overview

The human arm, from a biomechanical perspective, is a sophisticated system of levers and pulleys powered by muscles. The segment extending from the shoulder joint (glenohumeral joint) to the elbow joint (humeroulnar and humeroradial joints) is anatomically referred to as the brachium or upper arm. This region is structurally divided into two primary fascial compartments: the anterior (flexor) compartment and the posterior (extensor) compartment, each housing specific muscles responsible for a range of movements at both the elbow and, to some extent, the shoulder.

The Anterior (Flexor) Compartment Muscles

The muscles within the anterior compartment are primarily responsible for flexing the elbow and, in some cases, assisting with shoulder movements.

• Biceps Brachii:
  • Description: This iconic two-headed muscle is perhaps the most well-known muscle of the upper arm. Its name, "biceps," signifies its two origins (heads). The long head originates from the supraglenoid tubercle of the scapula (shoulder blade), and the short head originates from the coracoid process of the scapula. Both heads converge to insert onto the radial tuberosity of the radius and the bicipital aponeurosis.
  • Primary Actions: The biceps brachii is a powerful supinator of the forearm (turning the palm upwards) and a strong flexor of the elbow joint, particularly when the forearm is supinated.
  • Secondary Actions: The long head also contributes to shoulder flexion and stabilization of the humeral head within the glenoid cavity.
• Brachialis:
  • Description: Lying deep to the biceps brachii, the brachialis muscle originates from the anterior surface of the humerus (upper arm bone) and inserts onto the coronoid process and tuberosity of the ulna (forearm bone).
  • Primary Action: The brachialis is considered the purest elbow flexor. Unlike the biceps, its action is unaffected by forearm pronation or supination, making it the primary workhorse for all elbow flexion movements.
• Coracobrachialis:
  • Description: The smallest of the anterior compartment muscles, the coracobrachialis originates from the coracoid process of the scapula and inserts onto the medial surface of the mid-shaft of the humerus.
  • Primary Actions: Its primary roles are shoulder flexion (lifting the arm forward) and adduction (bringing the arm closer to the body). While not directly acting on the elbow, it is an important muscle within the upper arm's anterior compartment.

The Posterior (Extensor) Compartment Muscle

The posterior compartment houses the primary muscle responsible for extending the elbow.

• Triceps Brachii:
  • Description: The "triceps" (meaning "three heads") is the sole muscle of the posterior compartment. Its three heads originate from different points: the long head from the infraglenoid tubercle of the scapula, the lateral head from the posterior surface of the humerus superior to the radial groove, and the medial head from the posterior surface of the humerus inferior to the radial groove. All three heads converge to insert via a common tendon onto the olecranon process of the ulna.
  • Primary Action: The triceps brachii is the primary and most powerful extensor of the elbow joint, straightening the arm.
  • Secondary Actions: The long head of the triceps, crossing the shoulder joint, also assists with shoulder extension and adduction.

Functional Roles and Biomechanical Significance

Understanding the individual roles of these muscles is crucial for effective training and injury prevention.

• Elbow Flexion: Dominated by the brachialis (the primary mover) and strongly assisted by the biceps brachii (especially with supination).
• Elbow Extension: Solely performed by the triceps brachii.
• Forearm Supination: A powerful action primarily driven by the biceps brachii.
• Shoulder Stability and Movement: The coracobrachialis contributes to shoulder flexion and adduction, while the long heads of both the biceps and triceps play roles in stabilizing the shoulder joint and assisting with specific shoulder movements.

Clinical Relevance and Common Injuries

The muscles of the upper arm are frequently involved in sports-related injuries and overuse syndromes.

• Biceps Tendinopathy/Rupture: Inflammation or tearing of the biceps tendon, often at the shoulder (proximal) or elbow (distal) attachment points, common in weightlifters or those performing repetitive overhead movements.
• Triceps Tendinopathy/Rupture: Less common than biceps injuries but can occur with forceful elbow extension, such as in contact sports or powerlifting.
• Muscle Strains: Overstretching or tearing of muscle fibers due to sudden, forceful contractions or eccentric loading.
• Compartment Syndrome: Though rare in the upper arm, severe trauma can lead to swelling within the fascial compartments, compressing nerves and blood vessels.

Optimizing Upper Arm Strength and Development

To effectively strengthen the muscles of the upper arm, a balanced approach targeting both the flexors and extensors is essential.

• For Biceps Brachii and Brachialis:
  • Bicep Curls: Various forms (dumbbell, barbell, hammer, preacher) target elbow flexion. Different grips can emphasize the biceps' supination role.
  • Chin-ups/Pull-ups: Compound exercises that heavily engage the biceps and brachialis along with back muscles.
• For Triceps Brachii:
  • Triceps Pushdowns: Using a cable machine to extend the elbow.
  • Overhead Triceps Extensions: Targets all three heads, particularly the long head.
  • Close-Grip Bench Press: A compound exercise that significantly works the triceps.
  • Dips: Another excellent compound exercise for triceps and chest.
• For Coracobrachialis:
  • This muscle is typically trained indirectly through shoulder flexion and adduction movements, such as dumbbell front raises or cable adductions.

Always prioritize proper form, controlled movements, and progressive overload to safely and effectively build strength and hypertrophy in these crucial upper arm muscles.

Conclusion: A Foundation for Movement and Strength

The muscles located between the shoulder and the elbow—the Biceps Brachii, Brachialis, Coracobrachialis, and Triceps Brachii—form the core musculature of the upper arm. Together, they facilitate a wide range of movements at both the elbow and shoulder joints, essential for daily activities, athletic performance, and overall upper body function. A comprehensive understanding of their anatomy and biomechanics is fundamental for anyone looking to optimize their physical capabilities, prevent injury, or pursue a career in exercise science or rehabilitation.