Density, as it pertains to resistanct training, is amount of Work performed per unit time. And yes, “time” is critical here, because it's variable we're going to manipulate to ensure Progression, and a simple one at that.

(By way, Work equals Force X's Distance, and when we're talking engines and sports cars, it's called "Horsepower." I mention this, because everyone knows that, a bigger engine with more cylinders produces more Horsepower, all else equal. Same with your muscles.)

I won’t go into why Density Training works, other than to say it preferentially targets Intermediate Twitch Muscle Fibers, and also nutrient delivery / waste removal systems associated with these fibers, which means that these fibers and these systems will hypertrophy in response (sorry for science speak!). If you’re more curious about mechanism than that, you can buy my Advanced Training & Nutrition Guide, where I do go into a little more detail, while at same time, keeping it in laymen's terms. For now, here’s workout:

Let’s pretend it’s your day to train biceps. Here’s what you do:

You will perform Standing Curls (I like doing these with an Elastic Band rather than a dumbbell).