Sit on curl machine. Grasp lever handles with underhand grip. Align elbows at same pivot point as fulcrum of lever while placing back of arms up on pads.
Pull one lever handle toward shoulder. Return handle until arm is fully extended. Repeat with opposite arm. Continue alternating movement between arms.
Back of upper arms should remain on pad throughout movement. If machine has secondary lever (as shown), elbows can be positioned further away from primary fulcrum. Long head (lateral head) of biceps brachii is activated significantly more than short head (medial head) of biceps brachii since short head enters into active insufficiency as it continues to contract. Long head of Triceps Brachii is only significantly activated as antagonist stabilizer when it approaches passive insufficiency as elbow nears full flexion. See exercise performed with both arms simultaneously.
Antagonist Stabilizers (see comments)