Brachialis injury can mimic distal-biceps pain because both structures contribute to elbow flexion. The difference is that brachialis inserts on the ulna and does not create forearm supination. A patient with painful elbow flexion but relatively preserved painless supination therefore raises a different diagnostic question than someone whose symptoms are strongly reproduced by resisted supination.
That is a useful pattern, not a perfect rule. Pain can be shared, more than one structure can be irritated, and a nerve or the elbow joint can produce similar symptoms. The goal of the examination is to decide which structure is most likely responsible and whether imaging would change the plan.
Two muscles, two attachments
The front of the upper arm contains the biceps brachii, the coracobrachialis and the brachialis. The brachialis lies directly beneath the biceps, deeper and closer to the bone. It arises from the lower half of the front of the humerus and attaches to the ulna just below the elbow joint.
The biceps takes a different route. Its distal tendon crosses the elbow and attaches to the radial tuberosity on the radius. Because the radius rotates around the ulna, the biceps can turn the palm up. That is supination, and it is one of the biceps' main jobs.
The brachialis cannot do this. Its attachment on the ulna does not rotate, so it flexes the elbow in the same way whether the palm faces up, down or sideways. A 2025 ultrasound review described it as the workhorse of the elbow for exactly that reason (Manske, 2025).
| Feature | Brachialis | Distal biceps |
|---|---|---|
| Lower attachment | Ulna, just below the elbow joint | Radial tuberosity on the radius |
| Main actions | Elbow flexion in any forearm position | Elbow flexion and forearm supination |
| Resisted supination | Usually spared | Often painful or weak |
| Typical pain | Front of the lower arm and elbow crease | Deep at the front of the elbow near the radial tuberosity |
| Common imaging | Ultrasound for focal muscle injury; MRI for deeper damage | MRI, including FABS views, or ultrasound |
This table is a starting point for thinking about the problem. It is not a self-diagnosis tool.
What the 2025 ultrasound review found
A 2025 ultrasound review highlighted the brachialis as a source of anterior-arm pain and demonstrated how diagnostic ultrasound can evaluate its anatomy dynamically. The review reported that brachialis injuries are rare but can follow contusion, repetitive overuse or acute trauma such as forcing the elbow straight against resistance. It described repeated pull-ups with the forearm pronated, as in rock climbing, as a recognized source of brachialis strain or tendinopathy sometimes called climber's elbow (Manske, 2025).
The review also gave a practical clinical clue. With a brachialis injury, there may be some weakness of elbow flexion depending on the extent of the injury, while supination and pronation strength and range of motion should be spared. Severe injuries can reduce elbow extension.
Ultrasound offers real-time imaging, so the brachialis can be watched as the elbow and forearm move. Careful identification separates it from the biceps above it and from the nearby nerves and vessels in front of the elbow.
Why forearm position matters in the exam
Because the brachialis works the same in every forearm position, the exam deliberately changes forearm position while testing. A useful sequence compares:
- Resisted elbow flexion with the palm up, where the biceps contributes strongly
- Resisted elbow flexion with the palm down, where the biceps is at a mechanical disadvantage and the brachialis does more of the work
- Resisted supination with the elbow bent, which loads the distal biceps without relying on elbow flexion
If elbow flexion hurts in every position but resisted supination is comfortable and strong, the brachialis moves up the list. If resisted supination clearly reproduces the pain, the distal biceps or the bicipitoradial bursa is more likely. Elbow-flexion pain alone does not identify the distal biceps.
These are tendencies, not rules. The brachioradialis also flexes the elbow, the supinator muscle also supinates, and painful structures can influence how a person recruits every muscle around the elbow.
Brachialis rupture is rare but real
Isolated brachialis rupture is rare but documented. In one case, clinical examination and ultrasound identified an isolated tear after resisted flexion with the forearm pronated, and the patient recovered with nonoperative care. The authors noted that only five cases of traumatic brachialis rupture had been described in the previous 20 years, and that MRI is generally considered the most sensitive and specific method for demonstrating muscle injury (Schönberger, 2011).
This is case-report-level evidence. It shows that the injury exists and can be identified, not how often it happens or how every case should be treated.
Other structural patterns
Other case reports show that brachialis injury can take more than one form:
- Rupture with hematoma: a report described a brachialis rupture and hematoma in a 17-year-old male and reviewed previously reported cases (Winblad, 2008).
- Periosteal avulsion in a child: in a 7-year-old with elbow pain after trauma, a brachialis periosteal avulsion was initially misinterpreted on radiographs as a different avulsion fracture. MRI clarified the diagnosis, and the authors stressed that the injury may be overlooked because radiographic findings can be subtle (Lam, 2016).
These cases describe unusual injuries. They are not a basis for a treatment algorithm, and most anterior-arm pain is not a brachialis rupture.
Imaging the brachialis
Ultrasound is particularly useful when a focal brachialis muscle injury is suspected, while MRI can help characterize deeper or more extensive structural damage.
Ultrasound is well suited to:
- A focal muscle tear
- A hematoma
- Dynamic assessment while the elbow and forearm move
- Side-to-side comparison with the uninjured arm
MRI is more useful for deep structural injury, periosteal or bony involvement, a major tear or a differential that remains unclear. Imaging is most helpful when its result would change management.
Other causes of anterior elbow and forearm pain
- Distal biceps tendinopathy or partial tear: pain near the radial tuberosity, often with painful or weak resisted supination. A partial tear can have a normal Hook Test. See distal biceps tendinopathy vs. partial tear.
- Bicipitoradial bursitis: pain at nearly the same spot as distal biceps tendinopathy.
- Nerve involvement: burning, tingling, sensory change, neurologic weakness or symptoms spreading beyond a muscle pattern can reflect the radial tunnel, posterior interosseous nerve, musculocutaneous nerve or cervical radiculopathy. Nerve pathology is not diagnosed from pain location alone.
- Elbow joint: joint-line pain, locking, catching, loss of motion or swelling point toward the joint.
- Proximal biceps: pain at the front of the shoulder rather than the elbow is usually a shoulder problem.
What the exam includes
We take a careful history of how the pain began and whether there was a sudden forced-extension event. We palpate along the biceps, the distal tendon and the brachialis, test resisted elbow flexion with the forearm in different positions, test resisted supination, perform the Hook Test when a tendon injury is possible, check elbow motion, and screen the nerves and neck when symptoms suggest it. Findings are interpreted together rather than from a single test.
Rehabilitation depends on the diagnosis
A brachialis strain and distal biceps tendinopathy are both rehabilitated with progressive loading, but the emphasis differs. Brachialis rehabilitation concentrates on graded elbow-flexion loading, including the forearm positions that provoke symptoms, then pulling, climbing or lifting tasks. Distal-biceps rehabilitation should restore supination capacity rather than focusing only on curls. Return to climbing, lifting or sport is based on restored strength and tolerance rather than a set number of weeks.
Manual soft-tissue treatment may help selected cases where adjacent tissue sensitivity or restriction limits loading, as an adjunct to progressive strengthening. A substantial rupture, a large hematoma or a periosteal injury needs medical assessment first.
How Novo approaches the question
Novo starts by asking which structure is producing the pain. A brachialis problem and a distal biceps problem can feel alike, but forearm position, supination testing and, when needed, ultrasound or MRI usually separate them. Treatment is then matched to the diagnosis. See how we approach biceps, brachialis and anterior elbow pain.
References
- Manske RC, Wolfe C, Page P, Voight M. Diagnostic musculoskeletal ultrasound in the evaluation of the brachialis. International Journal of Sports Physical Therapy. 2025;20(8):1286-1291. PMID 40756795. (link)
- Schönberger TJ, Ernst MF. A brachialis muscle rupture diagnosed by ultrasound; case report. International Journal of Emergency Medicine. 2011;4(1):46. PMID 21791098. (link)
- Winblad JB, Escobedo E, Hunter JC. Brachialis muscle rupture and hematoma. Radiology Case Reports. 2008;3(4):251. PMID 27303568. (link)
- Lam JC, Lee KL, Griffith JF. Brachialis periosteal avulsion injury: case report with magnetic resonance imaging findings. Skeletal Radiology. 2016;45(11):1561-1564. PMID 27538972. (link)
- Caekebeke P, Meglic U, van den Bekerom MPJ, van Riet R. Evaluation of clinical tests for partial distal biceps tendon ruptures and tendinitis. Journal of Shoulder and Elbow Surgery. 2022;31(3):532-536. PMID 34774776. (link)
