Understanding your bicep anatomy helps you train more effectively. Let's break down the structure of your upper arm and how each component contributes to arm movement and appearance.
The Biceps Brachii
The biceps brachii is the primary muscle on the front of your upper arm. "Biceps" means "two heads," and "brachii" means "of the arm."
Long head:
• Position: Outer (lateral) side of arm
• Origin: Supraglenoid tubercle of scapula
• Creates the "peak" when flexing
• Crosses the shoulder joint
Short head:
• Position: Inner (medial) side of arm
• Origin: Coracoid process of scapula
• Creates width/thickness
• Also crosses the shoulder joint
Common insertion:
Both heads merge into a single tendon that attaches to the radial tuberosity (a bump on your radius bone, just below the elbow).
Functions of the Biceps
The biceps performs three main functions:
1. Elbow flexion: Bending your elbow, as in curling movements. This is the primary function trained in the gym.
2. Forearm supination: Rotating your forearm so your palm faces up. The biceps is actually a more powerful supinator than flexor.
3. Shoulder flexion: Raising your arm forward. A minor function, but the biceps does assist with this movement.
The Brachialis
The brachialis is often overlooked but crucial for arm development:
Location: Underneath the biceps, on the outer part of the arm
Origin: Lower half of the front of the humerus
Insertion: Ulna (the other forearm bone)
Function: Pure elbow flexor—doesn't supinate
Why it matters: A well-developed brachialis pushes the biceps up and adds width to your arm. It's visible between the biceps and triceps when developed.
How to target it: Neutral grip exercises (hammer curls) and pronated grip exercises (reverse curls) emphasize the brachialis.
The Brachioradialis
The brachioradialis is technically a forearm muscle but contributes to arm appearance:
Location: Thumb side of your forearm, extending up toward the elbow
Function: Elbow flexion, especially when forearm is in neutral position
Why it matters: Adds mass to the outer forearm and contributes to the "tie-in" between your biceps and forearm.
How to target it: Hammer curls and reverse curls heavily involve the brachioradialis.
The Triceps (For Context)
On the back of your arm, the triceps brachii ("three-headed muscle") provides important context:
Three heads: Long head, lateral head, medial head
Function: Elbow extension (straightening the arm)
Why it matters: Triceps make up about two-thirds of your upper arm mass. They're the antagonist to your biceps.
How These Muscles Work Together
During a curl:
• Biceps contract (shorten) to flex the elbow
• Brachialis assists with flexion
• Brachioradialis helps, especially in neutral grip
• Triceps lengthen (stretch) as antagonist
For complete arm development, train all these muscles:
• Biceps: standard curls (all variations)
• Brachialis: hammer curls, reverse curls
• Brachioradialis: hammer curls, reverse curls
• Triceps: pushdowns, extensions, dips, close-grip pressing
The Bottom Line
Your "biceps" is actually a complex of muscles working together. The biceps brachii (two heads) is the primary flexor and supinator, the brachialis assists with flexion, and the brachioradialis contributes from the forearm. Understanding this anatomy helps you select exercises for complete arm development.