Pre-Fatigue is a technique that has been used for quite a long time in the bodybuilding industry. It’s one of those “old habits die hard” techniques that many people consider to be appropriate.
The idea starts with the size principle.
In the body, you have muscle fibers, obviously, of differing size and ability. Smaller, slow twitch fibers are more appropriate for low-level contractions that can be maintained, such as the type of contraction you’d see with a low intensity run. From there, you have larger, fast twitch fibers, which are called upon when weight is heavier, a faster contraction is needed, the muscle fibers become fatigued, or some combination of all three.
While there are a bunch of different “sub fibers” (there are multiple “types” of small and fast twitch fibers) for the most part, we can categorize muscle fibers like this. Small and slow twitch; Large and fast twitch.
The size principle essentially states that when you first start lifting (as in that day) your muscle fiber recruitment, sort of “ramps up” based on need and fatigue. Muscle activation starts with the smaller, slow twitch fibers and then moves towards the large and faster twitch muscle fibers as they are required for contraction.
A lot of this recruitment comes from fatigue and also just because in order to lift some amount of weight, you’ll need to recruit these larger, stronger fibers.
When you do progressive warm up sets, you're essentially attempting to sequentially fatigue fibers and motor units, to encourage the activation of larger, faster ones, which increases your strength ability. That way, by the time you get toy our working sets, you have a larger amount of muscle being activated, to a greater extent, which allows you to lift heavier weight and hopefully, will lead to more muscle growth.
Because of this idea, many think that “pre-exhausting target muscle groups” will in essence, cause the recruitment of these larger, faster twitch muscle fibers and motor units, which should lead to greater muscle growth.Logically, since fatigue leads to higher threshold motor units and fibers being activated, this makes sense. But let's dive into how the process works, so you can make that decision for yourself.
The idea is like this:
In this scenario, we’re assuming that by using isolation movements first, you’re “pre-fatiguing” those target muscle groups. It’s then thought that you’ll recruit larger muscle fibers and motor units, leading to higher muscle activation and thus, the potential for growth.
Questioning This Theory
While intuitively, this sounds appropriate, you have to consider the order of importance of training and whether or not this is beneficial acutely or if it will actually translate to real growth.
Motor Unit Activation
The idea of fatiguing the muscle to encourage higher threshold (high threshold essentially means these motor units have a “high threshold of fatigue” that needs to be surpassed to be activated maximally) is actually sound.
The size principle seems to indicate that you do in fact need to “fatigue” muscle fibers to some extent in order to progressively activate muscle to higher levels.
Fatigue Vs. Activation
It is however important to distinguish fatiguing the muscle in order to activate higher threshold fibers versus simply becoming fatigued.
In one instance, (such as what you would progressively see over the course of a workout) you have fiber fatigue that actually leads to greater muscle activation. This, in my mind would in fact create an environment of greater muscle activation, which would be beneficial.
On the other hand, we have true fatigue, in which muscle activation actually diminishes. While higher threshold fibers and motor units may have been activated, the actual output of the muscle decreases, as you would see with actually being globally fatigued. (For example, your strength diminishes after a long workout. If simply fatiguing the muscle linearly improved muscle activation, you’d expect to be stronger at the end of a workout, right?)
Acute Fatigue vs. Total Volume (Acutely & Long-term)
These ideas lead me to my main argument against pre-fatigue – total volume.
Surely, there are many different methods of training that produce an “acute effect” but we also need to consider if using these methods will actually translate to a meaningful, long term adaptation.
Really, this can go for just about any advanced technique as well. Techniques such as BFR, Rest Pause, Reverse Pyramid Training and even Superset variants, all produce some acute effect that we hope translates into long-term growth.
In the case of pre-fatigue, we have to wonder if the acute effect is actually a beneficial one.
Look at Rest-Pause for example. This method certainly creates a large amount of metabolic stress, which would be an acute effect. Certainly, metabolic stress, when initiated over and over again, could potentially provide some long-term benefit.
However, the biggest reason it’s effective is because it allows for greater volume over time. You’re taking a weight that you’d normally lift for only a couple reps, and now performing that weight for 10-15. So essentially, while you’re having an acute effect, you’re also increasing volume, which is probably beneficial.
In the case of pre-fatigue, you’re certainly increasing fatigue of the muscle, but you’re also risking reducing total volume, both acutely and long-term if you continuously use this method.
The Research On Pre-Fatigue
For the most part, the research on this subject is pretty conclusive in that pre-exhaustion doesn’t provide much, if any benefit in terms of growth.
As we can see, it seems that using pre-exhaustion may be beneficial for triceps activation but for the most part, there doesn't seem to actually be much benefit for using this technique.
Overall, the evidence seems fairly conclusive that pre-exhaustion isn’t as beneficial as we’d hope. And really, that makes sense. Let’s summarize why pre-exhaustion is probably not the best route to take.
First, exercise order matters. Apart from the potential benefit, it makes sense that completing the most beneficial, complex and taxing movements first. The bench press for example, while not a fantastic builder of the pecs, requires a large amount of muscle to be recruited, in unison.
If these muscles are fatigued to a greater extent than is required for muscle recruitment, it’s likely that your performance, and thus volume or even strength ability will diminish. So essentially, while you may (or may not based on the evidence) increase muscle and motor unit activation, if you’re actually fatiguing the muscle, you’ll probably reduce your performance during the compound movements, that are supposed to be most important.
Second, at the hand of this reduction of performance, we have to consider if total volume, is more important.
Here’s an example.
You have two people. One uses pre-fatigue before bench press. The other person completes bench press first and then moves on to accessory movements.
Person 1, fatigues the muscle(s) before bench press. Muscle activation is higher acutely, but performance (and thus volume) is reduced.
Person 2 fatigues the muscle appropriately by progressively warming up. Their performance is not decreased, and in fact is better than last time. Volume increases relative to previous performance. They then complete accessory movements afterwards, increasing volume further.
Which do you choose? I can tell you, in my opinion, it’s best to opt for scenario 2.
Is Pre-Exhaustion Off Limits, Then?
Not necessarily. Just as with other advanced techniques, these methods produce some acute effect that might benefit you if used repeatedly.
I’m not going to sit here and say that pre-fatigue doesn’t provide any benefit. In fact it’s probably quite beneficial mentally in terms of being able to perform a complex movement, when fatigued.
This could translate to better performance for a laborer, a competitive athlete, a fireman, etc.
However, you have to consider long-term effect. While using this method occasionally, might provide some unique benefit, you have to consider that if you were to use this method always, your performance, volume and overall results will probably be less than if you opted to not use pre-fatigue.
Whereas a method like rest-pause provides both long and short term benefit (short - high level of metabolic stress / long - you're also increasing training volume significantly), the only potential benefit I can see from using pre-fatigue would be to create metabolic stress and potentially provide some mental benefit of training when fatigued.
While you can certainly implement this technique occasionally if you see fit, I strongly recommend against using this method as a primary focus of your training.
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