We always hear the expressions "Go to failure" and "Make sure you totally fatigue the muscle." Some people claim that failure and fatigue are the same
thing while others state they are quite different. Let us settle this common questions once and for all!
They're different and you need both. If you "go to failure," it means you cannot get another repetition during a given set. If you "totally fatigue a muscle," it means the muscle will no longer fire. The two are similar in the sense that they both imply having reached a limit, but they are different limits. Failure is functional; fatigue is physiological. Failure biomechanical; fatigue is biochemical. Failure has more to do with what's outside your body; fatigue has more to do with what's inside your body. Failure has more to do with a bodypart; fatigue has more to do with an individual muscle. Most important, going to failure does not mean you have totally fatigued the muscle you are working. It only means that the sum of the strengths of all of the multiple biomechanical systems, muscles and leverages involved in performing that movement has weakened to the point where it can no longer lift the weight. It does not necessarily mean that any of those individual muscles has been totally fatigued.
A grasp of this concept is crucial to bodybuilders, because it's possible to take every exercise to failure for the rest of your life and still not build muscle mass. You'll build strength, to be sure, because you are dividing the growth that occurs from your weight training among various muscle groups and improving their collective ability to lift a weight. The growth of the individual muscles in those muscle groups may be minimal in some cases, however, because you'll reach failure in your ability to perform the exercise before any of those individual muscles has a chance to be worked to its limit, or completely fatigued.
Our modern approach of progressive weight training, in which we start a bodypart workout with compound movements and finish with isolation movements, is intended to cover both failure and fatigue, thereby effecting both strength and muscle growth from the same workout. The initial compound exercise, taken to failure, builds overall strength in the bodypart and parcels out the resulting muscle growth among all the muscles in that bodypart. Compound bodypart "failure" exercises thus give us overall mass.
After failure of a bodypart is reached with a compound movement, we then focus on individual muscles in that bodypart by applying isolation exercises. These are intended to take each individual muscle the rest of the way to fatigue and enable it to grow independently of the rest of the bodypart. This is where we get the term "muscle separation."
The point so far is to warn you not to mistake failure for fatigue. Obviously, we need both, but whether we attain both is contingent upon getting the most out | of their relative exercises. That leads us to two other essential concepts: "proper performance of an exercise" and "intensity." Too often it's assumed that proper performance of an exercise is important only for isolation exercises. Not so. Without proper performance, failure also will suffer. If you are sloppy and cheat by swinging the weight with bodyparts other than the one you are trying to work, they will reach failure before the intended bodypart, and nothing will benefit from the exercise. In this regard, proper performance of an exercise may actually be more important for compound than for isolation movements.
The same consequence comes from not applying maximum intensity to every set. Intensity is a focusing of maximum effort, and it's the only way to fatigue all fibers of a muscle. Fatigue, then, takes over where failure leaves off. Once you reach failure, keep on going with isolation movements until you reach total fatigue. That's the purpose of forced reps. They liberate you from the limitations of bodypart failure, so you can keep pumping through smaller and smaller increments of the range of motion of the exercise until every fiber of that muscle will no longer fire.
For most, the rep ranges that work best are six to eight for taking a bodypart to failure and 10 to 12 for taking a muscle the rest of the way to fatigue. I advise that you try the same. Just remember, when you reach failure, your workout has only begun.