Are you training to fail?

Are you training to fail?
16 July 2014

I see so many people obsessed with numbers when weight training?

5 sets of 10?
4 sets of 8??
10 sets of 20???
If an exercise is carried out with a set number of repetitions specified beforehand, when you get to that predetermined number in your head that you have set for yourself to achieve, do you either just set the weight down or come to a halt on the machine?
Have the muscle fibres been fatigued?
What is the magic number?
"A muscle will only strengthen when forced to operate beyond its customary intensity and respond to that new stress imposed upon it"

A
old Schwarzenegger summed up this view when he said, "The last 3 or 4 reps is what makes the muscle grow. This area of pain divides the champion from someone else who is not a champion. That's what most people lack: having the guts to go on and just say they'll go through the pain, no matter what happens."
So is there a magic number of reps to carry out, or should we be going beyond predetermined numbers to exhaust the target muscle wherever that failure point happens to be?
Failure

Training to momentary muscular failure may provide greater stimulation to as many motor units and muscle fibres as possible and also to the higher threshold fast-twitch motor units which are capable of producing the greatest increases in strength and hypertrophy.
Beyond failure

Failure occurs unassisted, but there are methods that can be utilised to push the working target muscles beyond the threshold of failure.
Methods to help "go beyond" muscular failure using strict exercise form include:
Forced reps (getting someone to help you "spotting" to get a few extra reps.
Negatives (lowering the weight slowly when you get to failure)
Dropsets (continue an exercise with a lower weight after hitting failure at a higher one)
Rest-Pause (setting the weight down at failure and trying again to get a few extra reps after a brief pause)
Cheat reps (disregarding form for a few reps to get beyond failure)
Pre exhaust (performing isolation movements first – performing exercises that target the muscle directly then afterwards perform a compound movement that incorporates larger muscle groups to take the tired target muscle beyond failure)
Every set to failure?
However this also causes greater metabolic stress, more lactic acid, and more muscle fiber recruitment.
It has been shown training to failure every set increased resting levels of the catabolic hormone cortisol and suppressed anabolic growth factors such as IGF-1.1

To avoid this therefore one main working set to failure is all that is needed for each exercise, working up to this main set with warm up sets that are not taken to failure.
Why use magic numbers?