I have done some Escalation Density Training.
It is extremely hardcore.
(ie: Leg Workout)
PR set 1:
Squats
Leg Curls
10 minute Break
PR set 2:
Hack Squats
Stiff Legged Deadlifts
Here's how it works:
Choose a weight that you can do 10-12 reps with for each exercise.
Perform PR set 1 for 15 minutes in a continuous superset, only resting for the amount of time it takes to walk from the Squat rack to the leg curl machine and vice-a-versa.
Then take a 10 minute break, and perform PR set 2 in the same fashion.
The idea is to perform more work in the same given time, over a set period. Let's say you are going to train Legs using EDT for 6 weeks. On week one, you are able to complete 6 sets of squats, and Leg curls totalling 52 reps of squats, and 48 reps of leg curls. By week 6, you have become better conditioned and performed 7 sets of squats totalling 70 reps and 7 sets of leg curls totalling 68 reps. You will have become more efficient and will have forced your muscles to do more work over the same period of time.
You can do EDT for any body part. I believe that is is best to do a compound exercise supersetted with an auxillary lift. It is very demanding, and requires alot of aerobic capacity. You are working for 15 minute straight without a break!
There are also some nutritional suggestions including mega doses of tyrosine and Vitamin C ingestion an hour or two before training, followed by 100grams of Protein and at least 100 grams of Carbs post training.
Jay Schroeder(ex. Redskins&Raiders QB) and Adam Archuletta(Rams SS) are both really into this methodology of training.