Neural Factors of Fatigue and How to Manage Them

[philosopher]

Neural Factors of Fatigue and How to Manage Them
by Nathan J. Polencheck


Most of us don’t go to the gym to fail, right? Of course not. We’re there to succeed and reach our goals. At least, I hope that’s why—you guys there to pick up chicks, get out of the power rack. Anyway, for the success-minded athlete, the concept of failure sure is bandied about a lot by those “in the know.” Muscular failure, if you haven’t guessed by now, is the issue at hand.

For some schools of thought, achieving failure (or not, in some cases) is the defining point in determining whether or not a program will be successful. It seems that a great many arguments in the strength training world revolve around that single point. One doesn’t have to stray far to see this. Fortunately this article is not one of those arguments. Rather, I’ve chosen to inform instead of bicker.



HIT Upside the Head


The concept of achieving absolute muscular failure, or the so-called “momentary muscular ability,” can trace its origins back to the 1970s and the HIT school of bodybuilding. The HIT philosophy took its shape around the theories of Arthur Jones and Dr. Ellington Darden, and was personified by the late Mike Mentzer, a bodybuilder on par with Arnold in his prime.

A system claiming to value logic, knowledge, and empiricism, HIT can seem bullet-proof to many. Mike Mentzer’s elite-level bodybuilding physique, built by HIT’s methodology, only cemented this claim. Indeed, to its credit, it does encompass a general framework and set of principles that can be excellent for building muscle and developing general strength qualities when incorporated properly.

Unfortunately, a bad thing happened to HIT. Be it through logic, the salesmanship and business practices of Jones, or some measure of all, HIT was based upon a fundamental flaw: the idea that achieving muscular failure was not only desirable, but an absolute necessity for achieving muscular hypertrophy.

HIT’s measure of intensity, unlike the remainder of the exercise science world, is based on subjective effort. In other words, 100% intensity is pushing yourself to the point where you cannot achieve a full rep without assistance, a state referred to as concentric failure. The problem is that this measure of intensity (properly called intensiveness, a measure of subjective effort) has about as much to do with muscle growth as a good microbrew.

As later research into physiology would show, concentric failure is a predominantly neurological phenomenon. It doesn’t directly cause hypertrophic increases, though it can correlate with them. In simple terms, failure isn’t a requirement for getting bigger.

This leads to a whole host of problems with the rest of HIT’s prescriptions. Since training so intensively on a regular basis is taxing too many of the body’s systems, the workouts must necessarily be infrequent. Not only must the frequency decrease as the lifter becomes stronger and more advanced, but the volume used in each session must also decrease. This runs 180 degrees counter to what the bulk of research tells us about athletes, who must actually increase the total training stimulus as they become more advanced.

These assertions were supposedly based upon raw logic, and in the absence of any information to the contrary, it’s perfectly understandable how Jones and company came to those conclusions (though it’s a widely known rumor that Jones created the one-set-to-failure protocol for which HIT is most famous as a means of getting people out of his Nautilus gyms as quickly as possible). However, there’s been a lot of research over the past few decades that has given us new insight into the body’s processes, much of which overrides the logical extrapolations used by Jones and company. The HIT camp generally seems unwilling to change with the times however, for whatever reasons.

The point of this article is not to pick on HIT, though. HIT was discussed merely to provide a very convenient and easily recognized example to introduce the true subject. Specifically, I want to discuss just what failure is, its pros and cons, and how to use it effectively as a part of your bodybuilding and/or strength training program.

 

[philosopher]

How to Fail in Your Training


Muscular failure is actually a fairly complex topic. Strictly speaking, there are three types of muscular failure: concentric, isometric, and eccentric.

Concentric failure is exactly what I used in the example above: the inability to complete a repetition without external assistance (be it a partner or cheating). Isometric or static failure is the inability to hold a load in place. Eccentric failure is really more of an abstraction—as a thought experiment it can occur, but in practice it really can’t without an injury. Concentric failure is the commonly-accepted definition of failure used by those espousing the merits of achieving maximum effort on every set.

In order to understand the double-edged sword of concentric failure, a few points have to be considered. Firstly, what is the duration of the set? For the most part, failing on two reps will be similar to failing on six from a physiological standpoint. But what about twelve? Twenty? There’s a “strength zone” of reps, generally between the 1RM and 10RM, where failure can be primarily attributed to neurological factors. Beyond this, metabolic factors begin to take more and more precedence—it becomes a test of endurance instead of strength. For the purpose of this article, we’ll be considering the issue of failure as it applies to the strength zone.

So, what does the nervous system have to do with bodybuilding? Quite a bit. The nervous system is responsible for generating the impulses that cause all muscle contractions. The muscle itself is composed of multiple fibers, which are assigned into slow-twitch (ST) and fast-twitch (FT) categories. Each fiber is connected to a motor neuron originating in the brain. A motor neuron and all the fibers it connects to is called a motor unit (MU).

Motor units have activation thresholds—any stimulation from the nervous system below that threshold will not cause them to activate. Motor units are recruited according to the size principle, which more or less tells us that ST fibers are recruited before FT, and the FT fibers with the highest output are the last to be used. The highest-threshold MU’s require large amounts of tension to recruit.

There are a series of neural afferents, called proprioceptors, in muscle tissue that continuously provide feedback to the brain on the level of tension present in the muscle and allow the brain to adjust its output. This process is linked closely with cognitive control over motor function, and is capable of making very fine distinctions with regards to loads, force output, and rate of force development. Proprioception is responsible for the “feel” of an exercise.

As a set progresses, the smaller MU’s begin to fatigue. In order to keep up with the demands imposed upon the muscle, the nervous system begins changing things. Based on feedback from proprioceptors in the muscle, the nervous system increases the frequency of impulses (rate coding), and begins to recruit MU’s synchronously. Synchronous recruitment means that the nervous system will recruit every potential MU at once, instead of the usual asynchronous fashion (33). Failure occurs when the pool of MU’s recruited to lift the weight fatigue and the nervous system increases its output to activate other MU’s to take up the slack. This is more or less the same thing that occurs when achieving a maximal attempt. Due to the principle of specificity, the body will adapt to these firing patterns. This process of failure is both a good thing and a bad thing.

Bad news first. When consistently exposed to high-frequency impulses, the CNS has the peculiar trait of inhibiting its own output (12, 14, 17, 18, 19, 20, 21, 28, 29). This is theorized to be a protective mechanism, since consistent exposure to a high-intensity stimulus will be damaging to a neuron much the same way it would be to a muscle fiber, or any other tissue for that matter. Biological tissues are really nothing more than a means of transforming chemical energy into other forms; in the case of muscles, it becomes mechanical force, while in neurons it becomes an electrochemical impulse. If you demand too much and over-stress any of those tissues, they will become damaged and require a period of down-time in order to recuperate. The act of generating action potentials over and over, as is the case when maximal “push” is being put into a lift, is about the same thing as asking your muscle to perform 6 sets of 10 reps with 20 seconds of rest. It’s going to chew them up.

Up until recently there wasn’t a whole lot of research in this area to draw from. Lately though a large amount of research dealing with the topic of cortical motor output (neural drive) has been published, and it’s only reinforcing the idea that every period of high-intensity work requires a corresponding down-time for recovery (1-12).

Neural drive and fatigue is also directly linked to the individual’s state of arousal. It’s thought that this is because many of the structures that are responsible for motor output are the same structures that are responsible for emotion and arousal in humans, such as the basal ganglia and the reticular activating system (28). Having to get “psyched up” for a lift week after week can contribute to the neurological fatigue due to that fact. Many former Eastern bloc countries implanted this knowledge when designing their routines, having athletes avoid emotionally-taxing lifts as much as possible. They make a distinction between the “training max” and the “competition max,” with the former requiring little if any mental preparation. The arousal factor will prove to be the most telling in terms of how severely taxed the CNS is at any time, as focus and motivation can be easily determined by most people (not to mention manipulated by various supplements and well, “other” substances).

You’ve heard of people talking about “overtraining” the CNS? This is your boy right here. While there appears to be some benefit to switching up the exercises, as recommended by Westside for example, this may be because the body hasn’t accommodated to the movement, and a period of lowered intensity is necessarily brought about. A period of lowered intensity is a necessity after periods of high-intensity work, and it’s not all for muscular reasons. The mind needs a break as well, which is why one of the most common indicators of overtraining is lack of motivation to exercise.

Beyond the central fatigue that can develop in the brain, damage of a sort can also happen in the peripheral nervous system, at the neuromuscular junction and in the excitation-contraction coupling (ECC) system. The neuromuscular junction is where the motor neuron connects to the muscle. Excessive buildup of potassium ions (K+), which are normally required to transmit the nerve impulse from the neuron to the muscle, can cause a limited form of damage to the neuromuscular junction, inhibiting the transmission of impulses (4, 6, 7, 13, 22, 23). Intracellular K+ build-up occurs as a result of disruption to the muscle’s membrane during mechanical action, as well as during high-frequency neural firing, in a sort of feedback mechanism.

Past the neuromuscular junction, the ECC is formed by T-tubules that run deep inside the muscle, conducting the impulse and causing the release of calcium ions (Ca++) that cause the muscle to contract. Further research shows that when too much Ca++ is released inside the muscle, also as a result of high-intensity impulses, the ECC can become damaged and less responsive to nerve impulses (5, 13, 16, 32). Not only do you chew up your brain, but you’re grinding your nerves themselves into proverbial hamburger meat.

That’s a lot of bad news. Fortunately it has some good karma to balance it out. As noted by Dr. Zatsiorsky, there are three main ways to increase muscular tension (33). The two that are relevant here are the maximal-effort method and repeated-effort method. Maximal effort involves working with limit or near-limit loads, while repeated effort entails lifting a non-maximal load to muscular failure.

It’s pretty widely known that training with maximal weights causes extensive neural adaptation, resulting in almost immediate strength gains. This can also occur when the repeated-effort method is used. According to Zatsiorsky, the final “failure rep” causes strength gains as well, due to recruitment and fatigue of higher-threshold MU’s, and a wider array of total MU’s, through the processes described above (28, 33). So taking your sets to the limit is a good way to increase muscular strength as well as targeting a wide range of muscle fibers. As you could imagine, this is beneficial for folks interested in either strength or muscular size.

Not only that, but the neuron itself adapts to the stresses. It’s been shown that motor neurons exposed to high-frequency impulses end up with more developed neuromuscular junctions, apparently capable of handling high-intensity impulses better than those not exposed to similar stress (4, 6, 7). This is not unlike the way a muscle grows in response to the damage inflicted upon it. These adaptations to the junction seem to be fairly permanent (4,9).

Finally, all this metabolic and neural damage may well lead to additional hypertrophy via biochemical signaling. There’s been some recent work showing that a variety of satellite cells that tend to cluster around the NMJ, and K+ concentrations set off a biochemical cascade that may serve to activate them (34). There’s a whole mess of processes inside the fibers themselves that can be activated by the myriad chemical signals that result from both metabolic fatigue and eccentric trauma, and even the activity of nerve impulses themselves, so there’s definitely a case to be made for taking things to the limit.

 

[philosopher]

Learn From Your Failures


By now it’s pretty obvious that training to failure is a good thing, but it definitely has its drawbacks. The solution is pretty simple. You wouldn’t train for a true 1RM every single workout; why would you do it for a 6RM or a 10RM? That isn’t to say that training to a rep-maximum weekly won’t work. It’ll work exceedingly well over short periods of time, and even over longer periods if you’re willing to sacrifice the frequency of your workouts. It won’t last forever though, so you’ll do better finding a happy medium.

In one sense, HIT has things dead-on: If you’re training to your best, you won’t be able to train regularly. This couldn’t be truer. The caveat is you don’t have to take it to the max every time in order to see results. The max workouts should be infrequent yes, but that does not mean they have to be your only workouts.

In reality I’m not sure how much the minute details matter, if at all. Meaning, if you’re in the middle of a set and you think you might have one rep left, you haven’t necessarily cut yourself short by racking the bar. It also doesn’t mean that the guy that goes ahead and takes that last rep, and either has to fight it to the top, cheat, or get a spotter to help is going to be better off either. I’m convinced that factors like that, if they even matter at all, will only contribute to a tiny difference that would only be noticeable over years of training if ever.

There’s no clear-cut method for figuring out what is and isn’t fatiguing you centrally. The rule of thumb I like to use is based around your “psych” level. If you’re casually exerting yourself, then there’s likely not much going on. If you’re having to concentrate and focus to complete the set, you’re getting some stress, but nothing major. This is ideally where you’d want to fall for most of your workouts.

The final level would be when you’re going all out. Metallica (classic Metallica, not this St. Anger heresy) is blaring in your ear, you’ve head-butted the power rack three or for times, and you might have even taken a nice dose of stimulants. You’ve pushed it to the limit, and the set requires mental preparation before, as well as intense focus and drive during. This is when you’ve really pushed it into that zone of CNS fatigue.

By this point, it should be obvious that things have mushroomed beyond the simple matter of going to failure versus not going to failure. Muscular failure is really nothing more than a symptom of multiple underlying causes, mostly neurological. It is these causes which are relevant to the bodybuilder; limiting one’s self to the nervous system’s schedule is not conducive to maximizing hypertrophy gains.



So Why the Argument?


Why does HIT and its idea of reaching absolute failure garner all the negative attention? It isn’t due to the fact that they train differently than most. It’s the fact that in general, the HIT Jedi are more than willing to fire up their lightsabers and hack off the limbs of anyone that disagrees. Like a Jehovah’s Witness on Saturday afternoon, they want to go to everybody else’s house and tell them why they’re wrong.

As a system of bodybuilding, HIT will work fine for most people. In fact, I’d go as far as to say that in some of its incarnations it’d be ideal for a lot of people. It’s based on the concepts of recovery, hard work, and progressive overload, and while it does lack (okay, outright reject) any system of long-term planning, it will nevertheless produce results. There’s also the fact that many positive effects can come from training to failure, as noted. Whether those results are better, worse, or the same as other bodybuilding systems is unimportant to this article, and likely not worth worrying about.

What does matter is that the proponents of going to the max each and every time don’t leave it at bodybuilding. They routinely and regularly espouse their methodology as the only one that is appropriate for any type of strength training, including athletics. Now, even based on the fairly simple information laid out above, it should be fairly obvious why this isn’t the case.

It gets even better than that though. Most athletes in competitive sports don’t just need strength. They also require the ability to express that strength quickly, which is a whole different matter. Simply performing straight sets to concentric failure doesn’t account for this. Training to express force quickly requires sub-maximal weights that are moved with the intention of developing maximal speed with rest periods long enough to minimize fatigue, not maximize it as bodybuilders would want (28, 33). This, obviously, is fundamentally at odds with a belief system that requires concentric failure to occur in order to elicit any type of gain in strength or structure.

Not all athletes need to add muscle mass. For performance-oriented athletes, in every sport from baseball to hockey to football, sheer mass is only part of the issue. Adding mass can actually be a bad thing for some of these guys. The same goes for general strength. It isn’t always the concern, and a lot of athletes especially at the elite level would have their time better spent on other factors. The negative issues of training so infrequently and so stressfully will almost always have an impact on athletes, where neural adaptation is the rule.

Note that this does not mean that lifting a weight to failure is useless. For improving general strength levels and for improving muscle mass, it works tremendously well. This information only argues that HIT-type work must be used judiciously in the training of an athlete that has other concerns beyond simple gains in muscular size

 

[philosopher]

How to Get Around It: Cybernetic Periodization and Autoregulatory Training


Putting this information into practice, the approach can be as simple as doing most of your workouts in the “mild” zone and using every third or fourth workout as an all-out psyched-up max day. My personal favorite is working up to that all-out day over a three week cycle with the fourth week used for unloading and recovery.

In Supertraining, Mel Siff discusses the idea of cybernetic periodization. This is when the athlete’s own feedback is used to manipulate the training plan. The athlete judges his overall readiness by the Rating of Perceived Exertion (RPE), which is simply a scale of 1-10 (or 1-5 if you prefer) with 1 being least taxing and 10 being most.

The RPE scale would correlate to the arousal states mentioned previously. Low-effort, completely non-taxing work would fall in the 1-3 range, moderate effort would be in the 4-6 range, and heavy work would be from 7-10. This provides a convenient tool for longer-term planning. Using my preferred style, the workouts would turn out as follows:


Week 1 5-6
Week 2 6-8
Week 3 8-10
Week 4 < 4


Before discussing how to put this into practice, another topic needs to be introduced. Autoregulatory training is a concept related to cybernetic periodization, but used for planning the individual workout as opposed to the more general recommendations of RPE.

Using an autoregulating plan, the RPE would be used as a guideline from which the volume and intensity is then derived. During the mild weeks, exertion would be kept high, but not maximal. An example would be doing sets of a specific rep range with a given weight until it becomes taxing to do so, never truly hitting muscular failure. The heavier weeks would peak the exertion level, doing sets leading up to a true rep maximum. The unloading week would take around 60% of the rep maximum achieved and perform only a few sets with that weight.

This of course is only a very general example, as there are gradations of effort and specific training methods that can be implemented accordingly. Westside’s maximal-effort days and the Bulgarian weightlifting teams’ daily maximum are both examples. Even those techniques, and others, can be affected by the overall program design. However, given the scope of this article, this example is fine for conveying the basic idea.



How to Fail in Your Favor


I hope this piece managed to shed some light on the issue of failure. If you’re a bodybuilder, I don’t think it really matters too much if you train with a few really heavy sets and give it all you got, or a few slightly lighter sets that allow you to accumulate fatigue. As long as you’re lifting and getting stronger, as well as meeting your nutritional requirements, I’m really not convinced it makes that much of a difference.

You’ll just as likely be better off alternating between the two approaches, as I noted above. There are many, many programs that do just that, including the one I outlined; you could use one of those to great success, or you could simply apply the concept to your existing workout. If you’re an athlete that uses strength training as just one facet of a larger program, you’ll definitely want to periodize and only utilize general strength training in the appropriate phases when it will be most useful.

As far as supplementation, there’s a variety of nootropic compounds out there that are becoming more and more popular. Caffeine, ephedrine, and similar compounds are helpful as they both work to increase arousal and focus via norepinephrine, but I don’t believe they’ll do much for restorative purposes. The amino acid L-tyrosine is a precursor to norepinephine, and in doses of 1-5g it can provide a stimulatory effect. Compounds like piracetam, vinpocetine and DMAE, the true nootropics, are making themselves known as cognition-enhancers, and can only help with focus and drive, as well as with recovery. Dopamine agonists can aid in neural drive as well, due to their mild stimulatory effects.

Finally, while I don’t have a reference for this, I would go out on a limb and say that creatine would also be something worth considering, due to its ability to enhance cellular energetics. It already shows the ability to attenuate brain damage during hypoxia; my hunch is that it will provide benefits here as well.

In closing, we have to remember that training is a complicated dance of stimuli and response. Our goal is to understand how to manipulate the stimuli in order to evoke the responses we desire. The information provided above should not be expressed as any singular key to success, but rather incorporated as what it is—another tool to help you on your way to controlling your body’s destiny. As diet and supplementation are used to manipulate the body’s hormonal systems, training can be structured to elicit similar effects. The ability to orchestrate the stress and recovery of the body’s systems is a critical and ultimately defining capacity for any athlete.

 

[philosopher]

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33. Zatsiorsky, VI. Science and Practice of Strength Training. 1995. Human Kinetics.

34. Powell JA, Molgo J, Adams DS, Colasante C, Williams A, Bohlen M, Jaimovich E. IP3 receptors and associated Ca2+ signals localize to satellite cells and to components of the neuromuscular junction in skeletal muscle. J Neurosci. 2003 Sep 10;23(23):8185-92.

 

[tim290280]

Great post Philo!!

 

[FlexCabana]

wow great read

 

[Flex]

The final level would be when you’re going all out. Metallica (classic Metallica, not this St. Anger heresy)

Hey! I liked the song frantic.

 

[patdiddy]

Great read Phil........

 

[Rocky]

Nice one Philo!

 

[PrinceVegeta]

^^ delete pls...


nice post philo!

 

[Zigurd]

You must spread some Reputation around before giving it to philosopher again.

FUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU

Amazing read man.

 

[tim290280]

Good bump PV!

 

[Big_Guns_Lance]

What a great read! Thanks philo