Legs!!! No just kidding...just wanted to quote about every other person in the gym anymore. I think I would agree that biceps is likely the most dreaded, not arms just biceps for some reason. Love the pump from legs, shoulders, and back. Although I pay the horrible price later in the day, each time, after leg day no matter if its a high rep, high weight, mid both, etc...legs just lock up and Im stuck in the baby position the rest of the evening.