The biceps brachii is a muscle group targeted for both strength and aesthetics, but it is composed of two distinct parts that require varied training angles. Achieving complete development, including both muscle height and overall width, requires training beyond simple elbow flexion. Full arm development depends on understanding how different exercises emphasize specific parts of this complex muscle unit. By strategically changing the position of the shoulder and forearm, specific muscle heads can be preferentially activated, leading to a more comprehensive physique.
How the Biceps Complex Works
The biceps brachii, meaning “two-headed muscle of the arm,” is composed of the long head and the short head. Both heads originate on the scapula and insert into the radius, a forearm bone. The muscle’s primary functions are to flex the elbow and supinate the forearm (turning the palm upward). Because both heads cross the shoulder joint, they also play a minor role in shoulder flexion.
The long head is located on the outer side of the arm and creates the visible “peak” when the muscle is flexed. Its activation is highly sensitive to shoulder position because its tendon travels over the shoulder joint. The short head lies on the inner side of the arm and primarily contributes to the overall width and thickness of the muscle belly.
Beneath the biceps brachii lies the brachialis, a separate muscle that attaches to the ulna. The brachialis is a powerful elbow flexor that does not participate in forearm supination. Developing the brachialis is essential because its growth pushes the overlying biceps upward, enhancing overall arm girth.
Emphasizing the Long Head
To maximize the growth of the long head, the shoulder must be placed into extension, positioning the elbows behind the torso. This position stretches the long head at the shoulder joint, increasing its mechanical advantage and forcing it to take on a greater proportion of the load during the curl. This pre-stretching is a key biomechanical principle for selective activation.
A classic movement for this is the Incline Dumbbell Curl, performed on a bench angled back to 45 or 60 degrees. Allowing the arms to hang straight down behind the body puts the long head under tension before the lift begins. Maintaining a fully supinated (palm-up) grip throughout the movement further assists the bicep’s function, helping to engage the long head fibers.
Another effective technique is the Drag Curl, performed with a barbell or cable. The elbows are pulled back and the bar is “dragged” up the front of the body, continuously emphasizing shoulder extension. For all exercises targeting the long head, a slightly narrower grip width can also help direct tension toward the outer fibers of the muscle.
Emphasizing the Short Head
The short head is emphasized when the arm is placed into shoulder flexion, fixing the elbows in front of the body. This angle shortens the long head, putting it at a mechanical disadvantage and forcing the short head to become the dominant flexor. This manipulation of the shoulder joint is the most effective way to isolate the short head.
The Preacher Curl is the most common exercise to achieve this positioning, as the pad locks the upper arm in front of the torso. This fixed position maintains constant tension on the short head throughout the entire range of motion. Using a wider-than-shoulder-width grip on a barbell or EZ-bar during preacher curls can also help shift more workload to the inner, short head fibers.
Another highly effective movement is the Concentration Curl, where the elbow is braced against the inner thigh. This positioning also fixes the arm in a slightly flexed position and produces high activation of the biceps muscle overall. Focusing on a powerful squeeze at the top of the range of motion during these movements helps maximize the contractile stimulus.
Developing Overall Arm Thickness
Building true arm size requires training the brachialis and brachioradialis, which contribute significantly to the visual thickness of the arm. The brachialis sits directly beneath the biceps brachii, and its development increases the total cross-sectional area of the arm. The brachioradialis is a prominent forearm muscle that assists in elbow flexion, especially when a neutral grip is used.
These muscles are best targeted by using a neutral (palms facing each other) or a pronated (palms facing down) grip. When the forearm is pronated, the biceps brachii is at a mechanical disadvantage, making the brachialis the primary elbow flexor. The Hammer Curl, performed with dumbbells and a neutral grip, is the signature movement for targeting the brachialis and brachioradialis simultaneously.
Reverse Curls, performed with a pronated grip, place the biceps brachii in its weakest position for elbow flexion, maximizing the involvement of the brachialis. While these movements might use lighter weights than traditional supinated curls, they are indispensable for creating the “stacked” look of the arm. Training these deep muscles pushes the superficial biceps higher, enhancing the peak and overall muscularity.