"Do dumbbell flys first and then the barbell bench press because it puts more emphasis on the chest!"
You have probably heard this statement before, because it is based on the well-known principle of pre-exhaustion (sometimes called pre-fatigue). This is often used by bodybuilders and is also recommended a lot - especially to help with your weak points.
Pre-exhaustion training: first do an isolation exercise and then a multi-joint exercise for the same target muscles.
The hypothesis is that a muscle group will be worked more during a multi-joint exercise if you pre-exhaust it with an isolation exercise. This is not about supersets without rest between exercises, but about regular sets.
To give a few examples: If you do a few sets of leg extensions first and then a few sets of squats, the squats will supposedly hit the quads more than if you do them before the leg extensions.
Similarly, the chest activation in the bench press should be higher if you do flys beforehand. Also, the deadlift should do more for your hamstrings if you do leg curls beforehand.
By training with pre-exhaustion, the pre-exhausted muscle group should be used more during the compound exercise.
You probably understand the principle. And as always, we want to get to the bottom of it and ask ourselves: Is that really the case or wouldn't it just be better if I did the bench press first and then the flys - in other words, just train "normally?"
"Normal" training is used here to mean training in which the compound exercise is performed first, followed by the isolation exercise.
Let's take a look at what the studies on the subject have to say. If we zoom out and take a bird's eye view of the results of all the relevant studies on the subject, we see NO clear result.
Some studies show that it works and some studies show that it doesn't work. Most show that it doesn't work the way we might imagine.
In fact, it appears that it is not the pre-exhausted muscle group that is more stimulated; rather the other supporting muscle groups are proportionally more stimulated during the multi-joint exercise.
For example, a study by Brennecke et al. (2009) shows the following: If flys are performed first, then the subsequent bench press uses proportionally more of the triceps and NOT the chest.
If we think about it more carefully, it actually makes sense: the chest is pre-exhausted and therefore the other supporting muscle groups step in and do more of the work to get the bar up.
However, despite the higher activity in the supporting muscle groups, the bench press performance is obviously worse overall than when the bench press is performed fresh with the chest not pre-exhausted. After all, the chest is the muscle that contributes the most to the exercise when the bench press is performed normally.
The supporting muscle groups cannot compensate for this 100% - even if they step on the gas a little more. This phenomenon, where the supporting muscle groups are loaded more, is also shown in many other studies.
Many studies show that it is not the pre-exhausted muscle groups, but rather the other supporting muscle groups that are more stimulated during the following multi-joint exercise.
However, there are also some studies that paint a different picture. Among them, for example, is a study by Artur et al. (2017).
On the one hand, they also came to the conclusion that the chest is not more stressed during the bench press if it is pre-exhausted by doing flys beforehand. On the other hand - and this is astonishing - they found that triceps activity was higher during the bench press if a single-joint triceps exercise was performed beforehand.
Now you might be asking yourself: "Huh? How does that fit together? If you pre-exhaust the chest, it does nothing for the chest, but if you pre-exhaust the triceps, it does something for the triceps? That doesn't seem logical!"
Yes, that may seem illogical at first glance. But if we think about it more closely, it turns out not to be so illogical.
However, some studies show that pre-exhaustion actually makes the pre-exhausted muscle group work harder in the following compound exercise.
What comes next is pure speculation about why this might be and what the resulting logical conclusions might be for our own training.
If we do the bench press with a normal or wide grip, then the chest should be the limiting factor. If we can't get the bar up, then it's because the chest can't do it.
The triceps and anterior delts should still have a bit in the tank, but this doesn't do much because they are very ineffective at helping to move the bar when compared with the pecs.
So the chest is already the limiting factor in the bench press anyway. If we now also pre-exhaust the chest, then nothing changes: the chest remains the limit. Therefore, pre-exhausting in this case does nothing (at least nothing good) for the chest.
But now imagine that you fatigue your triceps before the bench. The triceps are not normally the limiting factor for the bench press. But if they are sufficiently pre-exhausted, then they could very well become the limiting factor.
This results in a much greater strain on the triceps during the bench press. After all, the chest is no longer the limit, and the triceps are thus brought much closer to THEIR limit. Therefore, MORE muscle fibers are activated in the triceps and these are then activated even STRONGER.
Incidentally, the study by Artur et al. (2017) mentioned above shows the same phenomenon for the anterior delts as it does for the triceps.
If you pre-exhaust the anterior delts by doing front raises and then do the bench press, then the anterior delts will be more stimulated. This is probably also because the pre-exhausted anterior deltoid is the new limiting factor in the bench press, rather than the chest.
Limit of an exercise
Accordingly, we cannot make a blanket statement: pre-exhaustion brings something or pre-exhaustion brings nothing. As always, it depends on the context.
If a certain muscle group is the limiting factor in a compound exercise, then there is probably no point in also pre-exhausting this muscle group with an isolation exercise. The muscle group is already the limit anyway. However, if it is not the limit of the compound exercise, then pre-exhaustion might do some good.
Training with pre-exhaustion does no good if the pre-exhausted muscle group is the limiting muscle in the multi-joint exercise anyway (even without pre-exhaustion).
For example, if you have to lean far forward to get down on the squat and the movement is mainly on the glutes, then doing leg extensions first and then the squat might do some good - that is, assuming you WANT more quadriceps stress on the squat.
Another example would be the deadlift: If your lower back tends to limit your deadlift strength, then it might help to first pre-exhaust your hamstrings by doing leg curls so that your hamstrings are more engaged in the deadlift - again, assuming you WANT the hamstrings to be more engaged in the deadlift.
When you work with pre-exhaustion, however, you must also be aware of one more thing: You will be able to handle less weight and/or fewer reps overall in the compound exercise.
For example, if you perform the squat with pre-exhausted quads, then you will manage less weight and/or reps. This means that in total less muscle mass will be used during the squat.
If you want to put up with that in order to better stress your weak point, then of course that's okay! For a very advanced athlete, for example, this could be a good plan to bring up a lagging muscle. For beginners, however, it is less of a good idea, because it is much more important for beginners to build balanced muscles everywhere.
By training with pre-exhaustion, you will manage less weight and/or fewer reps in the subsequent multi-joint exercise and thus use less muscle mass in total.
Let's get to the heart of the pre-exhaustion issue. It is only worth working with pre-exhaustion if the following three conditions are met:
- You have a major weak point in your physique and are no longer a beginner.
- The muscle group to be pre-exhausted is not the limiting factor in multi-joint exercise already.
- It's worth it to you that you'll use less muscle overall in the multi-joint exercise if you pre-exhaust one muscle group.
If these three conditions are not met, it is better to train in the classical style - that is, first the compound and then the isolation exercise.
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