The brachialis is a muscle that sits beneath the biceps brachii, and its development is a direct factor in achieving arm width and thickness. While the biceps receive most of the attention, the brachialis pushes the biceps upward, giving the illusion of a higher peak and significantly adding to the circumference of the upper arm. Developing this often-overlooked muscle requires specific exercise selection and technique adjustments that prioritize its unique function over the more dominant biceps.
Understanding the Brachialis’ Role in Arm Flexion
The brachialis is situated deep to the biceps brachii, originating on the lower half of the humerus and inserting onto the ulna. This anatomical connection means the brachialis functions exclusively as a pure elbow flexor. Because it inserts on the ulna and not the radius, it is completely independent of forearm rotation and does not assist in supination or pronation.
The brachialis is the primary elbow flexor, with some research suggesting it can generate around 50% more power in this action than the biceps brachii. The biceps, while also a powerful flexor, also acts as a supinator, the muscle that turns the palm upward. To isolate the brachialis, the goal is to eliminate the biceps’ mechanical advantage in rotation, forcing the deep muscle to take on the majority of the lifting effort.
Exercise Selection for Maximum Brachialis Activation
Targeting the brachialis requires choosing movements and grips that minimize the biceps brachii’s involvement as a supinator. The most effective way to achieve this is by utilizing a neutral (hammer) or a pronated (overhand) grip. This places the forearm in a position where the biceps cannot contribute effectively, shifting tension to the brachialis and the brachioradialis.
The dumbbell hammer curl is the most recognized exercise for this purpose, as the neutral grip (palms facing each other) removes the supination element from the biceps. To enhance activation, the cross-body hammer curl variation is effective. The dumbbell is curled across the body toward the opposite shoulder, which forces greater recruitment of the brachialis and further minimizes biceps involvement.
The reverse curl uses a pronated grip on a straight bar or EZ-bar, with the palms facing down. This overhand grip puts the biceps in their weakest position as an elbow flexor. This makes the brachialis and brachioradialis the primary muscles responsible for lifting the weight, forcing the brachialis to work significantly harder to flex the elbow.
The Zottman curl provides a unique stimulus by combining movements that target both the biceps and the brachialis. This exercise involves curling the weight up with a supinated grip but lowering it slowly with a pronated grip. The pronated lowering phase, known as the eccentric, places a substantial, controlled load on the brachialis and drives muscle growth.
Optimizing Technique and Training Variables
To maximize growth, technique must prioritize isolation and mechanical tension over lifting heavy weight with poor form. For the brachialis, a full range of motion is important, particularly the full stretch at the bottom of the movement. Research suggests that training in the initial angles of elbow flexion promotes greater distal muscle hypertrophy. Therefore, every repetition should begin with a fully extended arm, ensuring the brachialis is stretched under load before initiating the lift. Momentum must be minimized, meaning the torso should remain stable without swinging or rocking. This strict execution ensures the brachialis is doing the work.
The use of a controlled tempo, especially during the eccentric phase, is a variable for hypertrophy. The lowering portion of the lift should take approximately three to four seconds, as this extended time under tension causes muscle fiber damage. Slower eccentric movements have been shown to increase the cross-sectional area of the elbow flexors, driving muscle adaptation.
Because the brachialis is a smaller muscle often recruited during back and biceps training, it responds well to a moderate volume of direct work. Integrating two to three targeted brachialis exercises into a routine, performed two to three times per week, provides an optimal frequency for recovery and growth. Aiming for three to four sets of 8–15 repetitions per exercise, focusing on feeling the muscle work, will provide the necessary stimulus.