Bicep Muscles: Anatomy, Functions, and Training Implications

What muscles are in your bicep?

The term "bicep" most commonly refers to the biceps brachii, a two-headed muscle prominently located on the front of the upper arm, but functionally, elbow flexion and forearm supination also heavily involve other crucial muscles like the brachialis and brachioradialis.

Understanding the "Bicep" Region

When most people refer to the "bicep," they are typically thinking of the large, visible muscle that bulges on the front of the upper arm. While this is indeed the biceps brachii, it's crucial for fitness enthusiasts, trainers, and kinesiologists to understand that arm flexion and strength involve a coordinated effort from several muscles, each with distinct anatomical origins, insertions, and primary functions. Recognizing these individual contributions is key to effective and balanced training.

The Biceps Brachii: The Star of the Show

The biceps brachii is perhaps the most well-known muscle of the upper arm, famous for its role in creating the "peak" of the arm. True to its name, "biceps" meaning "two heads," it originates with two distinct heads:

• Long Head: This head originates from the supraglenoid tubercle of the scapula (shoulder blade), just above the glenoid cavity. Its tendon passes through the shoulder joint capsule and over the head of the humerus, giving it a unique role in shoulder stability.
• Short Head: This head originates from the coracoid process of the scapula, a small, hook-like projection.

Both heads merge to form a single muscle belly, which then inserts primarily onto the radial tuberosity (a bony prominence on the radius bone of the forearm) and, via the bicipital aponeurosis (a fibrous sheet), into the deep fascia of the forearm.

Primary Actions of the Biceps Brachii:

• Elbow Flexion: Bending the elbow, bringing the forearm closer to the upper arm. This action is most powerful when the forearm is supinated.
• Forearm Supination: Rotating the forearm so that the palm faces upward or forward. The biceps brachii is a particularly strong supinator, especially when the elbow is flexed.
• Weak Shoulder Flexion: Assisting in raising the arm forward at the shoulder joint.

The Brachialis: The True Powerhouse of Elbow Flexion

Often overshadowed by the more superficial biceps brachii, the brachialis is, in fact, the primary and strongest elbow flexor. It lies deep to the biceps brachii, directly attaching to the humerus and ulna.

• Anatomy: It originates from the anterior surface of the humerus (the upper arm bone) and inserts onto the coronoid process and tuberosity of the ulna (the larger forearm bone).
• Primary Action: Pure elbow flexion. Unlike the biceps brachii, the brachialis's action is unaffected by the position of the forearm (supinated, pronated, or neutral). This makes it the workhorse of arm bending, regardless of grip.

The Brachioradialis: The Forearm Contributor

While technically a muscle of the forearm, the brachioradialis plays a significant synergistic role in elbow flexion and is often considered when training the "bicep" region, especially with neutral or pronated grips.

• Anatomy: It originates from the lateral supracondylar ridge of the humerus (just above the elbow joint on the outside) and inserts onto the styloid process of the radius (near the wrist on the thumb side).
• Primary Actions:
  • Elbow Flexion: Most effective when the forearm is in a neutral (hammer) grip position.
  • Pronation/Supination to Neutral: Assists in moving the forearm towards a neutral position from either full pronation or supination.

Synergistic Muscles in Arm Flexion

Beyond the primary muscles discussed, other muscles contribute to the overall movement and stability of the arm during "bicep" exercises:

• Coracobrachialis: A small muscle located deep to the short head of the biceps, assisting in shoulder flexion and adduction.
• Forearm Flexors: Muscles like the flexor carpi radialis and ulnaris, while primarily involved in wrist flexion, contribute to grip strength which is essential for holding weights during bicep curls.

Functional Significance and Training Implications

Understanding the distinct roles of the biceps brachii, brachialis, and brachioradialis is crucial for designing comprehensive and effective training programs:

• Targeting the Biceps Brachii: Exercises performed with a supinated grip (palms up, e.g., standard bicep curls) emphasize the biceps brachii due to its strong supinating action. Slight variations in elbow position (e.g., incline curls for the long head, preacher curls for the short head) can subtly shift emphasis.
• Targeting the Brachialis: To specifically target the brachialis, exercises where the forearm is pronated (palms down, e.g., reverse curls) are highly effective. Since the biceps brachii is less efficient in this position, the brachialis takes on a greater load. Neutral grip (hammer) curls also heavily recruit the brachialis.
• Targeting the Brachioradialis: Neutral grip curls (hammer curls) are excellent for engaging the brachioradialis, as this muscle is optimally positioned to flex the elbow in this forearm orientation. Pronated grip exercises also engage it significantly.

Developing all three of these muscles contributes to overall arm size, strength, and functional capacity. Neglecting the brachialis and brachioradialis by solely focusing on supinated curls can lead to imbalanced development and potentially limit overall elbow flexion strength.

Conclusion: A Coordinated Effort

While the biceps brachii may be the most visually prominent muscle, a truly strong and well-developed "bicep" region is the result of a coordinated effort from the biceps brachii, brachialis, and brachioradialis. Each muscle plays a unique and indispensable role in elbow flexion, forearm supination, and overall arm function. By incorporating a variety of grip positions and exercise types into your training, you can ensure comprehensive development of all the muscles that contribute to the power and aesthetics of your upper arm.