4) 21s

One of the most complicated biceps exercises. Because it’s made up of three consecutive sets with no rest in-between, the exercise is also great for endurance. Also because of its composite nature it shapes the biceps all over.
The subject takes hold of a barbell (make sure it’s less loaded than the one you do your usual barbell curls with, otherwise you stand no chance to last the distance) curls it upward but stops mid-distance and lowers it from there. One needs to do seven reps of this. Then, after the seventh rep he/she goes all the way to the top of the motion but only lowers the weight to half distance and lifts it back up from there. He/she does seven more reps of this, then, without stopping, seven full barbell curls.
This’ll blast the biceps like nothing else.
Extra considerations: - when fatigue starts settling in, be extra careful not to cheat.