Flip your grip, blow up the forearms.
Keep your wrists firm and elbows tucked, the overhand grip hits the brachialis and forearms hard.
Flipping to an overhand grip takes the biceps out of their strongest position, which forces the deeper elbow flexors and the forearms to pick up the slack. Curling the bar with your knuckles leading builds the brachialis underneath the biceps and thickens the forearm muscles that normal curls never touch. It is the finishing move for arms that look strong from every angle, not just the mirror-facing one.
Because the overhand grip puts the biceps at a mechanical disadvantage, which is the entire point. Expect to use noticeably less weight than a normal curl and treat it as a precision movement, not a strength contest.
Both work. A straight bar is the strictest version, while the angled EZ grip sits more comfortably in the wrists for a lot of lifters. If your wrists complain on the straight bar, the EZ bar is the easy fix.
The brachialis, the muscle underneath the biceps that pushes the whole arm out when it grows, plus the forearm muscles along the top of your forearm. It fills in the gaps a palms-up curl leaves behind.
