In weight training, training to failure is to repeat an exercise movement (such as the bench press) to the point of momentary muscular failure. Contrary to widespread belief, this is not the point at which the individual thinks they cannot complete any more repetitions, but rather the first repetition that fails due to inadequate muscular strength.
Training to failure is, however, a controversial topic. The proponents of High Intensity Training — Mike Mentzer, Arthur Jones and Ellington Darden — advise training to failure on every set. But other experts believe that this will lead to overtraining, and suggest training to failure only on the last set of an exercise .
Some practitioners recommend finishing a set of repetitions just before the point of failure; e.g. if you can do a maximum of 12 reps with a given weight, only perform 11.
Others extend the training to failure concept and recommend performing 3-4 reps beyond failure by mildly compromising correct form in order to increase "burn".
Main uses for training to failure Edit
By training to failure, one fatigues enough of the muscle fibres to prevent lifting a particular weight. Combining training to failure with drop sets allows fatiguing more fibres with each set. In fact doing drop sets without first training to failure with a heavier weight, or not training to failure on each drop set, will not yield optimum results, so drop sets may be considered a form of training to failure.
Training to failure is mainly considered a hypertrophy training technique, as muscular strength, power, and endurance gains can still be made without training to failure. However one might argue that if you can physically do more, then you are not training at your optimum level, so it may be considered a general principle for any aspect of training, even cardio/aerobic training such as running or cycling (until you physically cannot continue), but again this increases the risk of injury, of collapsing, and of feeling extreme discomfort for the next few days.
Repetition Max (RM) Edit
Working out your Repetition Max (such as your 1RM) must be done to true failure, so this also can be considered a form of training to failure. Though 1RM is the most popular and commonly used, any number of reps can be used, for instance a 10RM or 15RM, in fact your 10RM weight will be much more useful for you in terms of training than your 1RM, and can be performed with a much lower risk of joint injury (due to the lower weight). Your 10RM would be the weight at which you can do 10 repetitions, but fail to fully lift the 11th rep.