There is no doubting the fact that using full repetitions is the best way to develop muscle strength throughout the entire range of motion, and as a result, is the best thing to build muscle size and fullness.
But, this is bodybuilding and when did we ever stop pursing greater and greater gains?
Sometimes it pays to go above and beyond and really push the limits. But, what do you do if you cannot achieve one more single full repetition?
One thing you can do is try to get some partial reps in. As the name implies, partial repetitions are repetitions performed throughout a partial range of motion. During which portion of the range of motion you perform your partial repetitions is up to you and what you wish to get out of the exercise.
Partial repetitions work because the body is naturally stronger in a static or near-static position. This means that although you are incapable of complete another full repetition, there is still more gas left in the tank which you can use to perform partial repetitions to fatigue the muscle fibres even deeper.
A range of 6 to 12 inches is a good choice for partial reps.
To push things even further, when you can no longer do partial repetitions you may wish to perform a static hold. A static hold is nothing more than holding the weight in a static position. You are even stronger in a static position than you are in a partial rep, so it is an ideal to perform repetitions in the following order: for reps, partial reps, static holds.
While I definitely recommend using partial reps from time to time, like I have said many times before, sometimes stressing the central nervous system too much can result in overtraining — so for the natural bodybuilder, such practices are best used sparingly.