It is a discussion that has gone on for decades–train to failure or not? There are good arguments on both sides but I have to ask “Why not fail?” Yes, I am a proponent of taking sets to failure. Should it be every set? Maybe. However, I know that some amount of sets taken to failure is necessary to build muscle. I can tell you this from my own personal experience. I don't care what magazine articles say, what books say or what anyone tells you because I have lived it.
What Happens When You Fail?
As I am sure you are aware, muscle growth occurs when muscle fibers are torn and forced to rebuild themselves. Going to failure insures that the muscle fibers are sufficiently damages to force the body to make them grow. You also tip the metabolic scale when you push things that hard. Intensity can be had in many different ways. Failure is just one of those many ways. However, it is quite an effective way. I would not recommend taking many sets to failure, but I do think it has its place.
What Is Failure?
Failure is often misunderstood. Most people will stop far short of failure unless they truly get what failure is. I've seen it when training clients. I can clearly see they have more in them, but they stop short. They think they are fooling me, but I know better. Failure is when you cannot move the weight any longer with correct form. When you reach that point you can say you truly failed on your set and walk away a happy trainer. Anything less than that is not failure at all.
This is a seemingly lost art. Apparently intensity isn't something people really strive for today. In a recent article I discussed the origin of intensity in bodybuilding. I talked about how we can get that back. It is something you definitely should read.