Start: Attach a straight bar to the low pulley. Stand facing the weight stack, and grab the bar with a wide, underhand grip. Hold it at arm's length in front of your thighs, with our knees slightly bent, your back straight, and your shoulders back.
Finish: Curl the bar until your forearms are almost perpendicular to the floor, Pause, then return to the starting position.
Move your hands closer together to shift the demand from the inner to the outer portion of your biceps.