Weight training and bodybuilding training programs often use the term "train to failure." So what exactly does it mean?
While you will read different definitions of this, here is a general interpretation of this term.
Let's say your program says three sets of barbell arm curls of ten repetitions, that is 3X10 arm curls in weight training program language. Simply, training to failure means selecting a weight that is heavy enough so that the last exercise repetition (physical movement) taxes you such that you have difficulty completing the last one or two exercises in that set.
For example, the barbell curl number 10 of each and every set should be performed at an intensity such that you you have to struggle to raise the bar with good form.
Here is where some trainers differ. In my view, this does not mean absolute failure -- that you can't lift that bar and do that curl at all. It should mean that the last few repetitions are difficult but not impossible to do. You should then rest until you can do the next set to failure as well. You can manipulate the rest period between sets or the weight you lift to reach the ideal failure point for you.
The "failure" point is the intensity at which lactate / hydrogen ions accumulate and provide your muscles with the stress required to promote muscle growth.
