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:

1. Yielding: When you're maintaining a static position (like holding a plank).
2. Overcoming: When you're trying to move an immovable object.

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:

• Set up a couple of spotter arms or safety pins on a squat rack at about sternum height. They should be at a level height when your arms are bent at 90 degrees.
• Grab a barbell and curl it up against (underneath) the spotter arms so it's pressed firmly against them.
• Curl up against the pins as hard as you can for an 8-10 second count. You'll really feel your biceps and core fire up.
• Back away from the rack and perform 10-15 standard curls.