Bicep cable curls with a tip on better contraction on biceps brachii long head.
By sitting lower down and curling back behind your head, you’re engaging the long head of bicep brachii more as you are doing shoulder flexion. This will make your bicep peaks POP more, not because it trains the peaks (people say there are “peaking” exercises).
But this does give a great stretch and you will feel a great pump and it is hard to cheat in this position.
Extend the arms and also rotate the hands so you are pronated. As you start to curl, rotate the wrists to a supinated position. Keep the wrists from curling over and feel the squeeze and pause at the top of the movement.