It's a universal law: no curling in the squat rack. But there is one exception to the rule. Actually, there are two.
First, if you curl more than the other guy is squatting, you're permitted to do what you want in the rack.
The second exception to the rule is if you're doing "3D curls." Never heard of them? Well, this will be your new favorite curl.
What's a 3D Curl?
Any standard curl variation works your biceps through the concentric (lifting) and eccentric (lowering) phases. But the 3D curl incorporates all three types of muscle contraction: concentric, eccentric, AND isometric.
An isometric is when the muscle doesn't change in size while under load (no movement or change in joint angle). To get more specific, there are two types of isometric contractions:
The 3D curl uses overcoming isometrics to establish blood flow and maximal muscle fiber recruitment. In short, they'll trigger new growth. Here's how to do it: