Hypertrophy that is. In the past, I've told my clients that when it comes to hypertrophy, or building muscle, there's more or less a specific place on the continuum of the rep/set/load scheme where this takes place. Around 60-75% of your 1RM, 8-12 reps, about a minute rest. Along with that, the heavier the load with fewer reps resulted in strength gains with minimal hypertrophy and at the other extreme, low loads with high reps was for muscular endurance, simply put.
However, recent studies show that you can gain hypertrophy ANYWHERE along that spectrum, because the key factor in hypertrophy is VOLUME! So whatever rep/set/load scheme you're working in, you CAN build muscle! What you must be aware of, however, is that the high loads and low rep protocol favors type 2 /fast twitch muscle fiber hypertrophy whereas the low load high rep scheme favors the type 1/slow twitch fibers. Take a look at bodybuilders, they cycle thru all rep/load ranges, and they're, HUGE!
So, to build muscle, a couple key components are volume, frequency, and mechanical stress that's sufficient to elicit a response, and of course rest, nutrition, tempo etc.
So with that said, go get your pump on and get some gains people!!!