Brachialis

Function

Where it sits in the arm

The brachialis lies in the lower front part of the upper arm, deeper than the biceps brachii¹. It is in the arm’s front compartment, with the biceps and the coracobrachialis, a small muscle at the front of the upper arm⁵. Gray’s 1918 anatomy describes it covering the front of the elbow joint and the lower half of the humerus⁶. It forms part of the upper part of the antecubital fossa, the hollow at the front of the elbow¹.

Where it starts and ends

A 2025 review describes a strong, thick muscle running from the lower front of the humerus to the upper ulna².

In Gray’s account, the muscle starts at the deltoid’s attachment and reaches to within 2.5 cm of the elbow’s joint surface⁶. It also starts from the intermuscular septa, sheets of tough tissue that separate groups of muscles⁶. Its fibres meet in a thick tendon that attaches to the ulnar tuberosity, a bump on the ulna⁶. The tendon also attaches to a rough hollow on the coronoid process⁶. The coronoid process is a bony lip at the front of the top of the ulna, at the elbow.

Two studies of cadavers, bodies donated for study, measured the attachment on the ulna^7,8. Its average length was 26.3 mm in 20 elbows and 27.9 mm in 11^7,8.

Two heads, described in different ways

A 2007 cadaver study notes that published accounts of brachialis anatomy have conflicted, and that its own findings differ considerably⁹. Three studies describe two heads, superficial and deep, but differ on where each attaches^9,10,11:

• In 11 limbs, the larger superficial head ended in a thick round tendon on the ulnar tuberosity, and the deep head on the coronoid process⁹.
• In 240 limbs from an adult Sri Lankan population, the superficial head attached to the coronoid process and the deep head to the ulnar tuberosity¹⁰.
• In a study of 13 cadaver elbows by MRI, the one muscle that was dissected had two heads, and the superficial head attached to the ulnar tuberosity further down than the deep head¹¹.

The 11-limb authors suggest the superficial head may give most of the muscle’s bending strength⁹. The smaller deep head may help start bending from a straight elbow⁹.

What it moves

A StatPearls chapter calls the brachialis an important flexor of the elbow, meaning a muscle that bends it¹. It says the muscle bends the elbow in every natural position, and is considered a “pure flexor”¹. A 2020 paper explains that it attaches only to the ulna, so it has no role in turning the forearm¹². The same paper notes it makes the greatest contractile force of the elbow flexors¹².

In an MRI and dynamometer study of four men, the brachialis gave the largest share of the elbow’s bending torque³. Next came the biceps and the brachioradialis, a forearm muscle that bends the elbow³. A dynamometer is a machine that measures turning force.

Muscle	Share of elbow bending torque in four men (%)
Brachialis	473
Biceps brachii	343
Brachioradialis	193

How forearm position changes its activity

Studies have used electromyography (EMG), which picks up a muscle’s electrical signals, to compare forearm positions^13,14,15. Pronation is turning the palm down, and supination is turning it up. Each row is one study:

Who was studied	What they did	What was found
6 healthy men	Bent the elbow with no weight, in three positions	The brachialis activity pattern was similar palm up, neutral and palm down; the biceps patterns were not13
9 healthy people	Held the elbow bent while turning the forearm	The biceps was more active palm up; the brachialis and brachioradialis were more active palm down14
10 weight-trained men	Curled on a preacher bench, palms up and down	With either grip, the brachialis, both biceps heads and the brachioradialis were activated at similar levels to one another16
15 young healthy men	Bent the elbow as hard as they could	The three muscles were very active with the forearm neutral, fully turned down or fully turned up15

Its nerve and blood supply

In Gray’s account, the musculocutaneous nerve, which works the muscles at the front of the upper arm, supplies the brachialis⁶. It usually gets an extra filament from the radial nerve too⁶. A 2025 review says its blood comes from branches of the brachial artery and the recurrent radial artery². In dissection studies, how often the radial nerve shares the supply differs^9,10,19:

Dissection study	Specimens with a radial nerve branch to the brachialis (%)
20 cadaver arms	6519
240 cadaver limbs	8310
11 cadaver limbs	1009

A different kind of study tested the nerves in 100 patients¹⁹. Stimulating the radial nerve drew a response from the brachialis in 90% of them¹⁹. On average, the radial nerve’s share of the muscle’s supply was 11%¹⁹.

Breakdown

How often it is injured

A 2025 review states that brachialis injuries are rare². They can come from a contusion (a bruise from a direct blow) or from repeated overuse². A 2020 case report counted only 10 acute tears reported up to then, all in adults¹². A 2019 paper says isolated tears can look like a torn distal biceps tendon or a tumour within the muscle²⁰. That makes them hard to identify²⁰.

Tears in single case reports

A case report is a report on a single patient. Each row is one^20,21:

Who	How it happened	What was found
31-year-old competitive male weight lifter	A 40.8 kg biceps curl	The tendon was torn fully through at its attachment on the ulna20
35-year-old woman	Possibly strenuous gym exercise	An isolated tear, confirmed by MRI and managed without surgery21
8-year-old girl	A gymnastics move forced her elbows fully straight, or perhaps beyond12	A complete tear12
8-year-old boy	A fall on gymnastics bars	A complete rupture22

The authors reason that her brachialis would have been doing eccentric work when it tore, meaning muscle work done while the muscle lengthens¹².

Overuse in climbers and lifters

Climbing comes up in several reports^2,23,24:

• A 1990 report lists brachialis tendinitis among the soft tissue problems that replaced broken bones as climbers’ main injuries²³.
• A 2025 review states that repeated palm-down pull-ups in rock climbers may strain the brachialis or cause “climber’s elbow”, a tendinopathy (tendon pain with loading)².
• A 2023 review of indoor climbing injuries says brachialis injuries are seldom seen outside climbing²⁴.

The 2025 review also notes case reports of brachialis injuries in football, hockey, rugby and weightlifting².

Bone forming in the muscle

A 2021 review describes myositis ossificans as bone forming in soft tissue after injury²⁵. It names the brachialis as one of its most common sites, with the deltoid, quadriceps and adductors²⁵. A 2017 case report describes an 18-year-old man with no history of trauma²⁶. He had recently started regular gym workouts without supervision²⁶. A growing bony mass in his brachialis then limited elbow motion²⁶.

Recovery

How it grows with training

Training studies have measured brachialis size. Each row is one study^4,27:

Who was studied	Training	What was found
5 older men	12 weeks of heavy resistance training	Brachialis volume and cross-sectional area rose 22.6%, and the biceps 13.9%4
14 older men	12 weeks of elbow bending with one arm	The maximal cross-sectional area of the biceps and brachialis together rose 17.4% in the trained arm and did not change in the other28
21 untrained adults	12 weeks, incline curls on one arm and preacher curls on the other	Brachialis volume rose 21.1% after preacher curls and 17.1% after incline curls27

Cross-sectional area is the size of a slice cut straight across a muscle. In the 21-adult study, each arm did five sets of 10 at 70% of the one-repetition maximum, twice a week²⁷. That maximum is the heaviest load a person can lift once. The biceps grew more after incline curls²⁷. Total elbow flexor growth did not differ between arms, and in both, the biceps and brachialis grew more in their middle region²⁷.

What a single session shows

In a trial of twelve men, each arm was randomly assigned to a fast or a slow curl-type protocol at 60% of the one-repetition maximum²⁹. MRI signal changes showed the biceps was used preferentially in the fast protocol²⁹. The brachialis was used preferentially in the slow one, which spent five times as long lowering as lifting²⁹.

In 16 well-trained young men, four sets of one-arm dumbbell curls to failure swelled the biceps more than the brachialis³⁰. Muscle thickness rose 18.7% in the biceps and 12.3% in the brachialis³⁰. Brachialis swelling was similar after dumbbell curls and dumbbell rows³⁰. Europe PMC’s record of this study lists funding from Brazilian public research agencies; it does not state the funders’ role³⁰.

After a tear

Two single case reports describe the course after a tear^20,22. The 31-year-old weight lifter’s tear was managed without surgery²⁰. Ten months after the injury he was back to weightlifting and biceps curls, and he had full strength at final follow-up²⁰. The 8-year-old boy spent 3 weeks in a cast²². Two months after the injury, his elbow motion and daily use had no limits²².

After bone formed in the muscle

A 1992 case report, on a single patient, describes myositis ossificans of the brachialis in a 15-year-old football player³¹. After nine weeks of an exercise programme, he had regained full elbow motion³¹. At nine months, the new bone was nearly mature, and his elbow moved fully without pain³¹. His strength was normal, and he had returned to competition³¹.

Connections

The biceps above it

When a cup is lifted, the biceps brachii is the prime mover, and the brachialis helps as a synergist³². A synergist is a muscle that helps another make the same movement. The musculocutaneous nerve runs down between the two muscles and supplies both³³. In 13 elbows, microscopic examination found no direct link between their tendons¹¹. Above the elbow crease, the median nerve runs in front of the brachialis, between it and the biceps³⁴.

The radial nerve beside it

The radial nerve, the main nerve at the back of the arm and forearm, pierces the lateral intermuscular septum^35,36. It then runs between the brachioradialis and the brachialis^35,36.

The humerus and the elbow joint

The brachialis starts on the humerus and covers the front of the elbow joint⁶. Sources differ on its link to the joint capsule, the sleeve of tough tissue that encloses a joint^7,11. In 20 elbows, it attached through muscle and a tendon sheet to the capsule, the coronoid process and the upper ulna⁷. In 13 elbows, microscopic examination found no direct link between its tendon and the capsule¹¹.

In nine cadaver elbows, brachialis strain rose under varus (inward-bending) forces, peaking at 30 degrees of bend with the palm down³⁷. It rose significantly with both collateral ligaments cut, and the authors suggest the muscle may help steady the elbow against these forces³⁷.

Exercises that load it

Related exercise pages: biceps curl and pull-up^32,38. Studies of these exercises found these results:

Exercise	What studies found
Biceps curl	In 21 untrained adults, brachialis volume grew more after 12 weeks of preacher curls (21.1%) than incline curls (17.1%)27
Pull-up	In a computer model fed by motion tracking of 11 men with no history of shoulder pathology, front-grip pull-ups favoured the biceps and brachialis38

Sources

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Every source the library cites

Changes

• October 22, 2026 First published.