The weightlifting community has known about pre-exhausting a muscle with isolation movements for a long time and it is certainly not a new idea. But if you have reached a sticking point in a body-part that simply will not get stronger and grow any more than it currently is then this technique is highly recommended by many pros on the bodybuilding circuit.
If you use islolation moves to pre-exhaust your muscles If you pre-exhaust the muscles it will in turn make you have to use a lighter weight so we will look at a specific exercise like training your deltoids and getting some size to them. The wider your shoulders look the narrower your hips are going to look which increases the Adonis index for men.
This has now been proven to subconsciously be more attractive to women so there certainly is a lot of motivation to get broader shoulders. So when doing a pre-exhaust movement with a lighter weight than you would normally use you would then be doing things like lateral raises or bent over d/b raise or something like that.
Doing these types of exercises with a lighter weight before you go heavy will change your focus to think about your technique, your mind/ muscle connection as well as decrease your chance of injury. There is no doubt that training your shoulders using dumbbells rather than barbells will give you more control of your press.
Probably the biggest advantage of using dumbbells for your shoulders specifically is that they will allow you to isolate the individual muscles and concentrate on one specific area like your front, side or back delts. This is important when doing a pre-exhaust exercise to help you isolate and work the specific muscle you have in mind.
After a few sets of only 8 to 10 reps doing these specifically isolated movements you will notice that you simply cannot lift the weight that you normally train with and this is called pre-exhaustion. The objective would be to maintain your strength through this workout.
When you reach failure on your heavy sets then you can also increase the damage that you do by doing forced reps or negatives but do not do this more than once a week. If you do this more than once a week at the most you will have an over-training effect.