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Biceps Brachii

Key Points:
• Examination involves resisting elbow flexion as the biceps brachii flexes the elbow.
Muscle Function:
Flexes the elbow joint. The short head assists with shoulder adduction. The long head may assist with abduction if the humerus is laterally rotated.
Origin Fixed: Flexes the elbow joint by moving the forearm toward the humerus. In addition, supinates the forearm.
Insertion Fixed: Flexes the elbow joint by moving the humerus towards the forearm.
Palpation: During elbow flexion, the muscle belly on the arm can be palpated or the tendon, which is medial to the brachioradialis muscle, can be palpated. 
Strength Testing:
Gravity-lessened Test: Position – the subject in sitting with the arm supported at 90º of shoulder flexion, forearm supinated, 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 supination, and elbow in full extension. Stabilize – at the anterior shoulder when giving resistance. Resist – against elbow flexion when the forearm is supinated.
Possible Substitutions: Potential substitutions are brachialis, in which case the examiner can palpate for the biceps tendon within the cubital fossa medial to the brachioradialis with the forearm in supination. Additional substitutions are muscles responsible for wrist extensors and wrist flexors. To address this, make sure to keep the wrist relaxed.
Relevant Anatomy:
• Roots: C5, C6.
• Nerve: Musculocutaneous nerve.
• Innervation Route: C5, C6 → musculocutaneous nerve → biceps brachii branch.
Origin of Short Head: Apex of coracoid process of scapula. 
Origin of Long Head: Supraglenoid tubercle of scapula. 
Insertion: Tuberosity of radius and aponeurosis of biceps brachii (lacertus fibrosus).