A common best practice usually offered as advice to beginner bodybuilders is to do the core exercises using a ‘full range of motion’. This is sound advice and should be followed for the most part but occasionally it is useful to do partial reps.
So what is a partial rep? A partial rep is simply a rep done for only a fraction of the full range of motion. For example we all know that when doing the bench press the most difficult part is lifting the weight from your chest to about midway through the full range of motion.
The second half – raising the weight from the midpoint to the top of the range of motion-is considerably easier. This means that for this second half of the range of motion your muscles are underwhelmed by the amount of weight.
Taken to its logical conclusion, this also means that you are not training with full intensity and are “leaving some muscle growth on the table”, to use a favorite phrase. If you trained with a heavier weight during the second half of the range of motion you would stimulate your muscles more and gain both strength and size.
This is where partial reps come in. Say you are stuck at 225 lbs (2 x 45lb on each side + the 45lb bar) for the flat bench and are having difficulty moving up in weight. You could add 25lb weights on each side of the bar (for a total of 275) and then do just the upper half of the range of motion for several reps.
Do this several times over a few weeks and then try doing 275 lbs for the full range of motion. You will notice that it is now easier if not completely doable. That, my friend, is the power of partial reps! You can apply them to a wide range of exercises to catapult your results to the next level.
Strictly speaking, their primary use is to build strength but if you use a high rep range (above 10) you can also build muscle in the process. You might recall that the ideal rep range for hypertrophy (muscle growth) is 5-7 reps done in the full range of motion. This allows the muscles to be under tension for at least a minute, the minimal period necessary to stimulate growth.
Since partial reps are completed much quicker than normal full range reps, the time that the muscles are under tension is less than ideal. To compensate for this you need to do a lot more of the partial reps if you hope to induce muscle growth in addition to gaining strength.
An extra benefit of using partial reps is that they reduce the likelihood of injury. Most injuries occur when you train with too heavy a weight for a particular muscle or joint. With partial reps you are using a heavy weight all right, but only for the part of the range of motion that the muscles/joints can cope with. See? Partial reps are definitely safer.
Next time you find yourself hitting a plateau in weight for a given exercise, you now have another powerful tool in your arsenal!