Nervous Muscle

Understanding the Nervous System


[Editor's note: This article is complex, but it's kinda' like licking through a Tootsie Pop. If you're diligent, you'll get to the tasty Tootsie Roll filling. Similarly, if you furrow your brow and work your way through this article, you'll not only understand the nervous system a little better, but you'll also pick up a couple of neat training methods and some bits of information you can use to humiliate the average personal trainer or self-anointed gym guru. In other words, this is an article well worth licking through.]

It's very apparent to me that there are many coaches and fitness writers who don't understand the nervous system. I'm not the least bit surprised because your nervous system is arguably the most complex and ambiguous system in your body. If it wasn't as complicated as I claim, many of these "experts" wouldn't be falling all over their words when the topic comes up.

Now, my statements should not be considered spiteful or disrespectful. No one can be an expert in everything – especially when it comes to the human body. But the nervous system is my thing. I have a master's degree in Physiology, but my transcript is dominated by courses that analyzed how the nervous system controls muscle.

I was lucky enough to talk the head of the physiology department into letting me stay beyond my M.S. requirements so I could take many of the courses necessary for a PhD in Neuroscience. But even though the nervous system is my area, I'll be the first to admit that the more I study it, the less I feel like I know!

This is because each piece of research that's demonstrated often leads to a dozen other questions that no one can answer.

My point in telling you all of this is to iterate how complex the nervous system really is. I'm constantly studying it, and I still feel like I'm climbing a mountain that's getting taller with each step I take. So when I think about the fitness people who haven't even studied it, but drop neuroscience terms like first-period French, I get very, very scared.

Admittedly, such blatant ignorance can be rather amusing (to me, anyway).

By necessity, I now categorize most people who talk about the nervous system into two groups. Here they are:

1. The Well-Intended Group: This group consists of people who understand the importance of the nervous system, but they don't really know how it works.

2. The Insecure Group: This group often drops money words in their articles and lectures. These are words that they hope will somehow solidify their status as an expert. Unfortunately for them, many of the nervous system terms I often hear were obviously lifted out of watered-down texts from fitness authors who didn't know what in the hell they were talking about. Once the Insecure Group starts throwing around terms like "posttetanic facilitation" I immediately know they're doing their damndest to make themselves sound smarter than they really are. It ain't working.

Nervous System 101

Before I get to the nitty-gritty of the terms that I want to clear up, let me first give a brief overview of the nervous system (okay, it might not seem brief, but relatively speaking, it really is). Specifically, what is the nervous system?

There are two primary components of the nervous system known as the central nervous system (CNS) and the peripheral nervous system(PNS). The CNS is comprised of seven major divisions. Six of these divisions make up the brain. They are the medulla, pons, cerebellum, midbrain, diencephalon, and cerebral hemispheres. The seventh division of the CNS is the spinal cord. The PNS is divided into somatic and autonomic divisions.

Here's an elementary breakdown of each division that makes up the entire nervous system.

Brain: regardless of what your significant other sometimes tells you, you do have one. As mentioned, your brain consists of six divisions. Here are some basic functions – that we currently understand – of each brain division.

1. Medulla relays early information involving taste, hearing, balance, and control of neck and facial muscles.

2. Pons relays information pertaining to movement and sensation from the cerebral cortex to the cerebellum. It's also involved in respiration, taste, and sleep.

3. Midbrainlinks up your motor system with various parts of your brain. It also contains components that aid the auditory (hearing) and visual systems; along with regions that control muscles involved in eye movement. One important area of the midbrain that controls movement is the basal ganglia (more on this later).

4. Cerebellum this is an extremely important component of your brain that contains more neurons (ie, nerves) than any other brain structure. It receives sensory input from the spinal cord; motor information from the cerebral cortex; and information pertaining to balance from the inner ear. Also, it's important for maintaining posture; in addition to coordinating head and eye movements. Furthermore, it's helps you fine-tune your movements when you learn a new motor skill. Finally, it's also involved in language and other cognitive functions.

5. Diencephalon this brain division consists of the thalamus and hypothalamus. The thalamus transfers sensory information from the periphery (limbs, for example) to the cerebral hemispheres. Think of the thalamus as a relay station that determines whether or not sensory information reaches conscious awareness. The hypothalamus controls many vital functions such as growth, eating, drinking, and maternal behavior by regulating hormonal output from the pituitary gland. In addition, the hypothalamus is a key component that controls motivation and rewarding sensations.

6. Cerebral Hemispheres these are the largest regions of your brain. Some of the roles of the cerebral hemispheres are memory, emotion, social behavior, and control of fine movement. In addition, it contains structures with neurons that link similar regions of the right and left sides of your brain (yes, you have two similar sides of your brain that must be linked together).

(Importantly, none of the six aforementioned areas work independently. The nervous system is integrated on many, many levels. One such example is the association cortex. The association cortex consists of various motor areas that work together as a "committee" before any voluntary movement takes place.)

7. Spinal Cord - this structure extends from the base of your skull to the first lumbar vertebra. It receives sensory information from your skin, joints, and muscles of your trunk and limbs. In addition, it contains the motor neurons that are responsible for both voluntary and reflex movements. As a basic example, when you voluntarily curl a barbell, the information starts in your brain and travels down your spinal cord and out to your muscles where they dump the neurotransmitter acetylcholine that leads to contraction.

However, involuntary movements also exist. A good example of an involuntary movement is a reflex. This can be understood when the doctor taps your knee tendon to check your monosynaptic reflex (spinal reflex). The quick stretch of your quadriceps tendon sends sensory information into your spinal cord (from your knee joint) and quickly returns a motor signal back to your quadriceps so they'll contract. In other words, many reflexes don't "check in" with the brain before contraction occurs.

Take a deep breath because I'm almost finished with the overview.

The last component of the nervous system is the peripheral nervous system (PNS). This consists of the somatic and autonomic divisions. The somatic division is comprised of sensory neurons that innervate your skin, muscles, and joints. These peripheral neurons supply information to the CNS about your muscles and the position of your limbs. The somatic division is important to us weight-training types because it also consists of the neurons that innervate the muscles (motor neurons) that cause movement.

The autonomic division is much less exciting, but no less important than any other nervous system component. This division can be further broken down into the sympathetic, parasympathetic, and enteric systems. You've probably heard of the sympathetic system. It's also referred to as the "fight or flight" system. This is due to the release of hormones such as epinephrine that accelerates your heart rate.

The parasympathetic system can be thought of as the counteractive system to the sympathetic response. The parasympathetic system is often described as the "rest and digest" system since it aids in both. Finally, the enteric system causes your gastrointestinal tract to contract and relax to move foodstuffs through your digestive system – boring!

Moving Forward

So when you hear the term "nervous system" thrown around, in actuality, these are the components that make it up. Yikes, eh? And I can't stress enough that each system is integrated across many levels. In other words, virtually every division is constantly talking to the other (with the exception of that crazy enteric system).

Alright, so why did I put you through this review? First, I wanted to help you understand how complex that damn nervous system really is. Indeed, there's virtually no action that isn't in some way connected to the nervous system: motivation, pleasure, movement, digestion, hormonal secretion, etc, etc. But all you care about are your muscles right? Okay, I can live with that.

So let's say that I told you to perform a barbell curl. Now that you've been given an overview of the nervous system, you'll appreciate how many different areas work together before any movement takes place. Here's a graph that depicts what areas are working before you can curl that piece of iron.

Since each of these areas work in concert before your muscle contracts, it can be assumed that it's possible to improve muscle function by enhancing any of the areas depicted in the graph. What I'm trying to say is this: you could potentially increase or decrease the function of your biceps by toying with your basal ganglia. The same is true with your cerebellum, your association cortex, your upper motor neurons, your reflexes/motor programs, or your lower motor neurons.

But, believe it or not, most people aren't willing to have their brain or spinal cord split open – and subsequently hooked up to electrical devices – while performing a biceps curl. So we really don't know how some of theses areas can potentially change the action of your muscles.

Most research started at the endpoint of the above graph: the muscle. Hell, it's easily accessible and we know quite a bit about the components that cause your muscles to contract. But again, most people don't want to put themselves through muscle biopsies, and most don't want to have an electrode jammed into their lower motor neurons. So that's where those handy little mice come in.

Unfortunately, most mice and men are not created equal. So what might work great in mice for strength and size is much less likely to work for you or me. I digress.

Okay, I put you through this long-winded, albeit simplistic, overview of the nervous system so I could spend the next section laying to rest some serious nervous system mishaps that are becoming more ubiquitous than ever.

Honestly, this list could – and probably should – be much longer. Nevertheless, here are two terms and phrases that I frequently hear from the "not-so-informed, but I wanna sound smart" club.

Mishap #1. Post-tetanic Facilitation

I'm sure most of you have heard of wave loading. Basically, it consists of using varying levels of maximal loads in an effort to cause immediate strength gains. An example of wave loading looks like this:

Wave 1

Set 1: 5 reps with 300 lbs.
Set 2: 3 reps with 320 lbs.
Set 3: 1 rep with 340 lbs.

Then, with the neural enhancements that occur, you're able to repeat the above sequence with somewhere around 2% more load for each set. In other words, your 5RM, 3RM, and 1RM are enhanced so you can do this:

Wave 2

Set 1: 5 reps with 305 lbs.
Set 2: 3 reps with 325 lbs.
Set 3: 1 rep with 345 lbs.

Pretty cool, eh? Yep, it's a very effective method. Many have extolled the virtues of this method by giving credit to a nervous system response called post-tetanic facilitation. But apparently, post-tetanic facilitation isn't limited to just wave loading, I've heard it used in relation to holding a supramaximal load (ie, a load greater than your 1RM) in order to cause immediate strength gains, among many other methods.

So what's the problem? Well, when they use post-tetanic facilitation in reference to wave loading, supramaximal holds, or some other maximal strength method they don't know what in the hell they're talking about!

The first problem is the word tetanic. This term actually describes artificial electrical stimulation of the motor neuron that innervates your muscles (actually, it can be any neuron, but we're talking about the muscle).

If I wanted to get a tetanic response, I would either need to shock your motor neuron with an electrode, or use some type of electrical muscle stimulation (EMS) on the surface of your muscle. So when you hear the word tetanic, the person better be talking about electrical muscle stimulation (EMS). But 99.9% of the time, they aren't. But it doesn't end there.

The second problem is the word facilitation. This is just a fancy way of describing some type of neural enhancement. So what's the big deal? Simple, do you know how long the effects of facilitation last? About 20-200ms (yes, that's milliseconds).

If a neuroscientist saw a flyer for an upcoming lecture titled "Post-tetanic Facilitation," he would expect to hear information pertaining to artificial electrical nerve stimulation that lasts, at most, a few hundred milliseconds.

So what should they call this neural enhancement that leads to immediate strength gains? Post-activation potentiation. This is the correct term because activation describes a maximal voluntary contraction (ie, lifting or holding a maximal load) and potentiation refers to an effect that lasts for minutes, not milliseconds.

Post-activation potentiation is one of the most effective maximal strength building methods I've ever used. Not only will it cause immediate increases in maximal strength, but it can also be a great tool for building more muscle since you'll be able to recruit more motor units after the supramaximal hold. I even designed a program based on this outstanding method titled Primed For Muscle. link to]

If you want to jump right into supramaximal holds, you should give this method a try during your next squat or bench press workout. Here's what you should do.


Set 1: 5 reps with 70% of your 1RM
Rest 90s

Set 2: 3 reps with 75% of your 1RM
Rest 90s

Set 3: 3 reps with 85% of your 1RM
Rest 120s

Supramaximal Hold to Induce Post-activation Potentiation

Set 1: Hold 120% of your 1RM just short of lock-out for 10s.
Rest 45-60s

Set 2: Perform as many reps as possible with 90% of your 1RM
Rest 240s

Set 3: Hold 120% of your 1RM just short of lock-out for 10s.
Rest 45-60s

Set 4: Perform as many reps as possible with 90% of your 1RM

You'll gain both strength and size with this method. Perform it once each week for your heaviest workout. Your other weekly workouts should consist of submaximal loading protocols such as 4x8, 3x15, or 2x20, for example.

So if you ever hear a strength coach or fitness writer throwing around "post-tetanic facilitation" in relation to resistance training, you can be sure that their neuroscience studies were limited to the back of a Wheaties box.

Mishap #2. Recruitment of a Specific Motor Unit Pool

I love it when I hear a coach tell me how "Method X" recruits a specific motor unit pool. I mean, I'm quite entertained by it. How? Because I usually respond to such statements by saying, "Which motor unit pool and how are you identifying the motor unit pool?" At that point, the coach gives me a blank stare and takes off in a dead sprint.

Okay, let me give you a refresher. The motor unit consists of a motor neuron and all the fibers it innervates. If our muscles were a huge cartoon, a motor unit would look like this.

Motor units are classified into three primary categories. The first, and smallest, motor unit is the slow-twitch (S) variety that produces small amounts of force for long periods of time. Think of curling a pencil.

The second type is the fast-twitch, fatigue resistant (FR) that produces moderate amounts of force for moderate amounts of time. Think of curling a dumbbell for 100 reps. The third type is the fast-twitch, fast fatigable (FF) that produces large amounts of force for brief periods of time. Think of curling a dumbbell that represents your 1-3 repetition maximum (RM).

Importantly, each motor unit type can't be perfectly categorized. Indeed, there are hybrids of each motor unit type just like there are hybrid muscle fiber types (precisely the reason why there's hybrid motor units).

And based on the research by Denny-Brown, Pennybacker, and Henneman, we seem to know that there's an orderly recruitment of motor units. In other words, if you lift a small load, your S motor units will fire first; and if you lift a maximal load, your S motor units will fire first followed by the FR and FF motor units. This is known as the Size Principle.

Nolte J. The Human Brain. Mosby, Inc. pg 451. 2002

The above graph depicts what we think is happening at certain levels of force. What we do know is that there exists an orderly recruitment pattern of motor units from S to FR to FF. But what we don't know is how to differentiate when the shift occurs.

You see, we simply haven't developed the technology to measure specific motor unit pools during force production. Sure, there's the completely outdated electromyogram (EMG) that measures electrical activity from the surface of the muscle. But the practical application of EMG is basically limited to motor control and muscle disease. Other than those two situations, it results in nothing more than ambiguous pieces of data. Don't believe me? Here's what you'll typically get from an EMG analysis.

So the only information that a neuroscientist can derive from this graph is how the muscle recruits motor units during force production. The left side of the graph depicts the first motor units (apparently, the smallest motor units) that come into play.

With increasing levels of force, more and more motor units are recruited (hence, the plethora of lines that's measuring surface electrical activity). But it in no way differentiates between different motor unit pools. Anyone who tells you that a certain training method recruits a specific motor unit pool is banking on your lack of neuroscience knowledge. Now you're well-suited to fire back.

If you're training to improve maximal strength and size, then you need to recruit as many motor units as possible while training (you need to reach the upper right spectrum of the Size Principle graph). There are three ways to do this based on Zatsiorsky's Science and Practice of Strength Training.

1. Lift a maximal load.

2. Lift a submaximal load as fast as possible.

3. Lift a submaximal load to failure.

Most of my internet programs revolve around the first two methods, while some others use all three. But I usually limit the failure training to the concentric phase only. This is because isometric and eccentric failure can induce very high levels of fatigue. Generally speaking though, the risks associated with failure training rarely outweigh the benefits. So stick with the first two methods for the majority of your workouts.


Well, I've taken you through the nervous system and I've given some key pieces of information to use against gurus who try to overwhelm you with recondite language. Make no mistake about it, the nervous system is one complex monster. Now, I've got to get back to the books!