Mass building....the way I look at it, it's all mass building..the diet is what controls getting leaner, more detailed etc..I am always trying to stimulate growth....
One of my training partners is the most ectomorphic guy you have ever seen..really naturally thin at 6 foot tall with sky high metabolism...he has been with me for about 3 years now and went from 182, and just hit 220 last week 100% natural....people were constantly asking him why he was doing all the high reps with me...they don't ask him now, they ask if they can jump in..haha..
I like to mix reps...low, medium, high....do it all...