Pre-exhaust training is a resistance-training method where an isolation exercise is followed immediately by a compound exercise. This method enables you to take the larger muscles involved in the compound exercise to failure without running into limits imposed by the smaller muscles. If reaching failure is required to induce maximum muscle growth, and compound movements alone rarely take the targeted muscles to failure, then pre-exhausts help you overcome this limitation.

I don't know if Mr. Olympia competitor Mike Mentzer came up with the idea, but he definitely helped popularize it. Maybe Arthur Jones came up with it.

Take a bench press, say. The main muscles involved are your chest, shoulders, and triceps. But your triceps and shoulders are weaker than your chest; they will fatigue faster. So, although the idea of the bench press is to work primarily your chest, you won't be able to take it to failure if your shoulders and triceps give out first.

The solution: do an isolation exercise for the chest before hitting the bench. The pec-fly machine, for example, will work the chest in isolation while preserving the triceps and shoulders.

Here's a classic Mentzer-style pre-exhaust superset for the chest. After doing a light warmup on the compound exercise, in this case the bench, take the flyes to failure on a single set for six to ten reps, then immediately, ie without rest, proceed to the bench for another set to failure, one to three reps. Mentzer explains this workout in more detail in this video.

Not only will this approach allow you to take your pecs to failure on the bench and thereby induce maximum growth, it also has other benefits. One is that you require less weight on the compound exercise, leaving more room for progress in the gym. You also go easier on your joints.

Another example is the squat. The squat induces growth in basically your entire body, with the primary muscles worked being your quads. However, just as with the chest during a bench press, your quads are much stronger than the weaker muscles involved, meaning you won't be able to take your quads to failure on squats. Your calves, ankles, and knees can't handle the load your quads can. And some people can't load their spine with a lot of weight.

Mentzer's solution, as he explains in the same linked video, is to lightly warm up on the compound exercise, ie the squats. Next, take an isolation exercise, such as leg extensions, to failure, then immediately do the compound exercise, the squats, for just one more set to failure.

For the back, Mentzer suggested doing close-grip palms-up pull downs before the deadlift, but, as far as I know, he did allow rest in between. It may not have been intended as a pre-exhaust superset. Regardless, requiring grip strength on two back-to-back exercises isn't ideal if your grip usually gives out, as it does for me, before you've really taken your back to failure on deadlift. I could strengthen my grip in isolation, but I'd run the risk of overtraining, and there are other weaker body parts involved in a deadlift. I haven't tried this, but I suppose one could do some back exercise that doesn't involve grip strength, such as good mornings (with a weighted vest if necessary), and then do the deadlift.

Pre-exhaust workouts are brutal, but they work. I have been doing them for a few months and have been seeing tremendous growth and increases in strength. Try them at your own risk; I have given only a small glimpse into Mentzer's workout recommendations.