What is Brachialis?

What is Brachialis?

The brachialis is often called the workhorse of elbow flexion, yet most people have never heard of it because it hides underneath the more famous biceps. It sits on the front of the upper arm, deeper than the biceps, running from the lower half of the humerus down across the elbow to the ulna. Unlike the biceps, the brachialis crosses only the elbow joint, not the shoulder, and it attaches to the ulna, which is the forearm bone that does not rotate during supination or pronation. Those two facts define its behaviour: it is a pure elbow flexor that works no matter how the forearm is turned. When you curl with an underhand grip the biceps gets favourable leverage from supination, but the brachialis pulls just as hard. When you switch to a neutral (hammer) or overhand (pronated) grip, the biceps loses some of its advantage while the brachialis keeps working fully, so its relative contribution rises. This is why hammer curls and reverse curls are considered brachialis-biased. For anyone trying to build bigger arms, the brachialis matters more than its low profile suggests. Because it lies beneath the biceps, a well-developed brachialis literally pushes the biceps upward, increasing the apparent height or peak of the upper arm and adding width to the arm when viewed from the side. Developing it also improves overall elbow-flexion strength that carries over to rows, chin-ups and any pulling task. Understanding the brachialis as a single-joint, grip-independent flexor sitting under the biceps explains both how to train it and why neglecting it leaves arm development incomplete.

How it works

The brachialis produces elbow flexion by shortening between its origin on the humerus and its insertion on the ulna. It originates from the lower half of the anterior surface of the humerus, wrapping around the front of the bone, and inserts on the ulnar tuberosity and coronoid process of the ulna, just below the elbow. Because the ulna does not rotate, the brachialis has the same line of pull whether the palm faces up, sideways or down, making it the most consistent contributor to elbow flexion across all forearm positions. Biomechanics studies of elbow-muscle load sharing show that the brachialis carries a large share of flexion torque, and because it has a large physiological cross-sectional area relative to its size, it is a powerful flexor despite being hidden. Its role becomes proportionally greater when the biceps is placed at a disadvantage, which happens with a pronated or neutral grip and at certain elbow angles. Electromyographic work on the elbow flexors in trained lifters confirms that grip and forearm position shift the balance of activity among the biceps, brachialis and brachioradialis rather than isolating any one completely. In training terms, the brachialis obeys the same rules as any skeletal muscle: it grows from mechanical tension, an adequate number of hard weekly sets and progressive overload. Because it flexes the elbow in every grip, it receives some stimulus from all curling and pulling. To bias it specifically, you reduce the biceps' supination advantage by using a neutral grip, as in a hammer curl, or an overhand grip, as in a reverse curl. These grips do not remove the biceps from the movement, but they lower its leverage so the brachialis and brachioradialis do relatively more. The brachialis responds well to moderate rep ranges, controlled tempo and a full range of motion. Because it is a single-joint muscle with no shoulder involvement, shoulder position does not change its emphasis the way it does for the biceps long head or the triceps long head; the main levers are grip and load. A practical programme trains it directly with hammer and reverse curls while trusting that heavier supinated curls and pulling movements provide additional overlapping stimulus. One further practical point is elbow angle: because the biceps loses supination leverage and the brachialis has a favourable line of pull through the mid-range of flexion, the brachialis tends to carry a relatively larger share of the load in that middle portion of a curl. Training with a full but controlled range, pausing briefly where the movement feels hardest, keeps tension on the brachialis where it is most capable and avoids the temptation to shorten reps to lift heavier.

How to apply it

• Hammer curls (neutral grip): A neutral, thumbs-up grip removes the biceps' supination advantage so the brachialis and brachioradialis take on more of the load. Perform dumbbell or rope hammer curls for 8-15 reps with controlled form and a full range of motion.
• Reverse curls (pronated grip): An overhand grip places the biceps at a further disadvantage and strongly recruits the brachialis and forearm extensors. Use an EZ bar or dumbbells for 10-15 reps; expect to use lighter loads than on supinated curls.
• Cross-body hammer curls: Curling a dumbbell across the body toward the opposite shoulder keeps a neutral grip and provides a slightly different line of pull on the brachialis. Work for 10-15 controlled reps per arm, avoiding swing from the torso.
• Emphasise a full range and controlled lowering: Like any flexor, the brachialis benefits from being loaded through its full length. Lower each rep under control and reach a full stretch at the bottom rather than bouncing, which exposes the muscle to tension where it is longest.
• Progressive overload over weeks: The brachialis grows in response to gradually increasing demand. Add a little weight, a rep, or a set over time. Since it also works during supinated curls and pulling, modest direct volume of roughly 4-10 hard sets a week is usually enough.
• Pair it with biceps work: Train the brachialis alongside supinated biceps curls in the same session or week. Building both the deep brachialis and the superficial biceps produces fuller arms, since a bigger brachialis pushes the biceps upward and adds side width.

Worked example

A short weekly brachialis emphasis you can bolt onto existing biceps training. It uses neutral and pronated grips to reduce the biceps' supination advantage, so the brachialis does relatively more work, while keeping direct volume modest because pulling and supinated curls already contribute.

About 7 direct hard sets, added to your regular biceps and back work. If forearms or wrists fatigue before the upper arm, reduce reverse-curl load first, since the pronated grip loads the forearm extensors heavily. Rest 60-90 seconds between sets.

Brachialis vs biceps brachii

The brachialis and biceps are teammates in elbow flexion, not rivals. The brachialis works in every grip, while the biceps is favoured by an underhand grip. Because the brachialis sits underneath, developing it raises the biceps and widens the arm, so complete arm training includes both supinated and neutral or pronated curls.

By goal

• Strength and pulling performance: Use heavier neutral-grip work such as hammer curls and neutral-grip chin-ups in the 6-10 rep range. A strong brachialis boosts overall elbow-flexion strength that carries over to rows, pull-ups and grip-intensive lifts.
• Hypertrophy and arm width: Train 10-15 reps with hammer and reverse curls, full range and controlled tempo. A developed brachialis pushes the biceps up and adds thickness to the side of the arm, so include it in any arm-building block.
• Rehab and elbow health: After elbow irritation, neutral-grip curls are often better tolerated than heavy supinated ones because they distribute load across several flexors. Start light in a pain-free range and progress load gradually before adding pronated reverse curls.

Common misconceptions

• "The brachialis is a minor muscle you can ignore." The brachialis is a powerful primary elbow flexor that carries a large share of flexion torque. Ignoring it leaves arm development incomplete, since it sits under the biceps and its size directly affects the height and side width of the upper arm.
• "Hammer curls only train the forearms." Hammer curls do work the brachioradialis of the forearm, but their neutral grip also strongly loads the brachialis and still involves the biceps. They are one of the best movements for biasing the brachialis, not a forearm-only exercise.
• "You can fully isolate the brachialis." No single exercise isolates it. Every grip still involves the biceps and brachioradialis to some degree. Neutral and pronated grips reduce the biceps' leverage so the brachialis contributes relatively more, but it always works as part of a team.
• "Changing shoulder position targets the brachialis better." Because the brachialis crosses only the elbow, moving the shoulder does not change its emphasis the way it does for the two-joint biceps and triceps heads. Grip and load, not incline or arm-forward positions, are what shift work toward it.

Related terms

Brachialis FAQ

What does the brachialis do?

The brachialis flexes the elbow, bending the arm. Because it inserts on the ulna, which does not rotate, it flexes the elbow equally in any grip, making it the primary pure elbow flexor. It does not act on the shoulder or rotate the forearm.

Where does the brachialis originate and insert?

It originates from the lower half of the front surface of the humerus and inserts on the ulnar tuberosity and coronoid process of the ulna, just below the elbow. Crossing only the elbow joint, it is a dedicated single-joint flexor.

How is the brachialis different from the biceps?

The biceps crosses two joints, flexes the elbow and supinates the forearm, and sits on the surface. The brachialis crosses only the elbow, flexes it in any grip, and lies deeper. The brachialis works fully even when the biceps is at a disadvantage.

What is the best exercise for the brachialis?

Hammer curls with a neutral grip and reverse curls with a pronated grip bias the brachialis best, because they reduce the biceps' supination advantage. Cross-body hammer curls are another good option. All still involve the biceps to some degree.

Why does the brachialis make arms look bigger?

The brachialis lies underneath the biceps, so as it grows it pushes the biceps upward, increasing the apparent peak, and adds thickness to the side of the upper arm. This is why developing it produces fuller, wider-looking arms.

Do hammer curls work the brachialis or the forearms?

Both. The neutral grip of a hammer curl loads the brachialis strongly while also working the brachioradialis of the forearm and involving the biceps. It is one of the most effective brachialis-biased movements, not just a forearm exercise.

How many sets for the brachialis per week?

Because it also works during supinated curls and all pulling, most people need only about 4-10 direct hard sets a week of hammer or reverse curls to develop it. Count the indirect volume from rows, chin-ups and regular curls.

Can beginners train the brachialis?

Yes. Beginners already train it indirectly through any curling and pulling. Adding one neutral-grip movement such as a hammer curl is enough early on, since general elbow-flexion strength and size develop quickly without needing complex isolation.

References

1. Plantz MA, Bordoni B. Anatomy, Shoulder and Upper Limb, Brachialis Muscle. StatPearls, NCBI Bookshelf
2. Pigeon P, Yahia L, Feldman AG. The effect of elbow angle and external moment on load sharing of elbow muscles. J Electromyogr Kinesiol, 2010. PubMed 20452784
3. Naito A. Electromyographic study of the flexor muscles of the elbow articulation in weightlifting trained subjects. Electromyogr Clin Neurophysiol, 2007. PubMed 17375882
4. Schoenfeld BJ. The mechanisms of muscle hypertrophy and their application to resistance training. J Strength Cond Res, 2010. PubMed 20847704