Some critics of high intensity training like to make the claim that “training to failure is training to fail.” However, if you consider the real objective of exercise and what it means to train to momentary muscular failure (MMF) it becomes obvious the truth is the exact opposite; training to failure is really training to succeed.
Your goal when performing an exercise is to impose enough of a stress on your muscles and the systems supporting them to stimulate your body to adapt by improving their capabilities, making you stronger and better conditioned. The more intensely you work – the greater your effort relative to your momentary capability – the greater the stress and the more effective the stimulus for improvement. Your results from exercise are directly proportional to your intensity of effort and have more to do with this than any other training factor, including things like the load used, specific repetition methods, set and repetition schemes, etc.
When you begin an exercise, your intensity of effort is roughly equal to the percentage of your one repetition maximum you are using. If you are capable of lifting one hundred pounds one time in a specific manner, lifting only seventy pounds in the same manner requires only a seventy percent effort at the beginning of the exercise (repetition maximums are specific to the manner an exercise is performed, since different repetition methods, ranges of motion, repetition speeds, etc. can make an exercise harder or easier). As your muscles fatigue each subsequent repetition requires an increasing percentage of your decreasing strength, a greater intensity of effort. When fatigue has reduced your muscles strength enough that the force they are able to exert matches the force of the resistance you are working against and you reach MMF, you are working at maximum intensity.
If you quit an exercise before reaching MMF you may still stimulate improvements in muscular strength and size and other general, trainable factors of functional ability, but not to the same degree as you would if you continued to MMF and worked as intensely as possible. If you quit an exercise before reaching MMF you also will not know exactly how many repetitions you might have been able to perform; you won’t know if you would not have been able to complete another repetition in proper form, or if you could have done one, or two, or even three more. Without this knowledge it is difficult to evaluate changes in performance on a workout to workout basis which can be helpful in adjusting your volume and frequency of training to improve results.
So, several repetitions into an exercise when your muscles are burning, your heart is pounding in your chest, and every nerve in your body is screaming for you to quit, remember it is the last few hardest repetitions of an exercise and especially the very last rep when you achieve MMF that matter most, and ask yourself what is more important? Making the best possible progress towards your training goals? Or avoiding the momentary discomfort of continuing the exercise?
What does training to MMF really train you to do? It trains you to persevere through pain and discomfort to achieve your goals. It trains you to work even harder when things get tough, instead of quitting. It trains you to be stronger mentally as well as physically and builds even greater self-discipline that carries over to everything else you do. Training to MMF does not train you to fail; it builds and strengthens the traits that allow you to succeed.
Not training to MMF trains you to give up when things get uncomfortable. Not training to MMF trains you to avoid hard work. Not training to MMF trains you quit at something when you should be giving it everything you’ve got instead. Not training to MMF is what really trains you to fail.