Sit erect on the end of a flat bench, feet out in front and knees bent about 90 degrees. Grasp a fixed barbell out wide with an underhand grip, a hand position that puts more emphasis on the biceps short head. This will be your starting position.
Without using body English, do this partial-rep movement by contracting your biceps to curl the bar up to a point just below your chin, then release under control, ensuring the bar doesnâ€™t rest atop the thighs in the bottom position. Repeat for the designated number of reps.
Quickly reposition your hands to a shoulder-width grip and repeat for reps.
Finally switch to a close grip, which preferentially emphasizes the long head, for the final number of reps.