Very often, bodybuilding literature trumpets the need for full-range repetition in all bodybuilding movements in the gym.  This is important for beginner bodybuilders, who often will have wasted effort, in the best case, and injuries, in the worst case, from partial rep form.  We’ve all seen the man in the squat rack doing “power courtesies”, moving the weight down 2 inches while claiming to do squats.  We’ve all seen the teenagers on the flat bench with more weight than they can handle, pressing the weight through a 3-inch range of motion then high-fiving their friends on a set well done.  The truth is, for most trainers, partial reps mean the muscle is only doing partial work, and therefore not receiving the maximum potential for stimulation in the exercise.  In other words, partial reps equate to a great deal of wasted time in the gym.  However, for advanced trainers, partial repetitions can be useful when used at the conclusion of a workout for very specific purposes. 

As a finishing movement, partial reps have a place in bodybuilding routines.  Imagine you have just completed a full leg workout.  Your calves are cooked, your hams are fried, but you still feel like your quads have a little bit left in them.  Do you climb under the squat rack and attempt such a dangerous compound movement, well aware that your already taxed hamstrings and calves will be required as support muscles?  Of course not.  Instead, you should choose an isolation movement such as leg extensions, and complete several sets of full-range repetitions.  As you begin to feel the blood and lactic acid fill the quadriceps muscles, and realize full sets are no longer possible, attempt a few partial reps. Move the weight only halfway up, until you cannot move it anymore.  Then, move it one-quarter of the way up.  Then, move it one-eighth of the way up.  Continue until you are only moving the weight a fraction of an inch.  The muscle group will be engorged with blood, and you can rest assured you have pushed your quads to the limit in this workout! It works with other muscle groups as well, and can be a very effective way to finish off a body part.

To address a strength weakness, partial reps are useful as well.  If you are very strong in the first three-quarters of a bench press movement, yet notoriously weak in the bottom quarter, complete reps which keep the weight between the resting and one-quarter extension length.  In other words, keep moving the weight through only that section of the repetition in which you are the weakest.  It will challenge your body to improve in that area, and allow you maximum energy to work on those troubling areas.