The standard biceps curl is hardest at the mid-range, where the lever arm is the longest. But for variety we can change that, making the top or peak contraction the toughest part of the movement.
Lean forward at a 45-degree angle.
Don't drop the elbows down. Keep the upper arm in line with the body.
Perform curls in this position, squeezing hard at the top.
Charles Poliquin is a genius when it comes to devising innovative, painful exercises and his One-Arm Barbell Eccentric Curls are no exception. They're guaranteed to hurt, along with eliciting stares from other gym members.