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Key Points:

• Brachialis flexes the elbow joint.
• Very strong flexor, which is often neglected as a critical muscle group because of the more superficial and visible qualities of the biceps muscle.


Muscle Function:

Origin Fixed: Flexes the elbow joint and brings the forearm towards the humerus.
Insertion Fixed: Flexes the elbow joint and brings the humerus towards the forearm.
Palpation: During elbow flexion, the brachialis can be palpated in the cubital fossa medial to the brachioradialis muscle when the forearm is in pronation.
Strength Testing:
Gravity-lessened Test: Position – the subject in sitting with the arm supported at 90º of shoulder flexion, forearm pronated, and elbow fully extended. Stabilize – the anterior shoulder and support the forearm and hand. Support - the forearm through the range of motion.
Anti-gravity Test: Position – the subject in sitting with arm at side, forearm in full pronation, and elbow in full extension. Stabilize – at the anterior shoulder when giving resistance. Resist – against elbow flexion when the forearm is in pronation.
Possible Substitutions: Substitutions include muscles responsible for finger flexion. To avoid, keep fingers relaxed and palpate the brachialis muscle to confirm that it is contracting. Palmaris longus substitution can be detected by palpating the correct muscle. Flexor carpi ulnaris can be avoided by preventing ulnar deviation.
Relevant Anatomy:
• Roots: C5, C6.
• Nerve: Musculocutaneous nerve.
• Innervation Route: C5, C6 → musculocutaneous nerve → brachialis branch.
Origins: Distal ½ of anterior surface of humerus and both medial and lateral intermuscular septa.
Insertions: Tuberosity and coronoid process of ulna.