The Intelligent & Relentless Pursuit of Muscle™

The Science of 10 x 3
Enter the Nerve and Muscle Matrix

I recently gave a presentation amid professors, department heads, and graduate students in the College of Physiology at the University of Arizona. Due to my exercise-based background and studies in the fields of physiology and neuroscience, I guess they figured I’d be a viable candidate to tantalize their brain cells on a Friday morning. Between my backwoods anecdotes and haphazard laser pointing, I managed to traverse their critical inquiries virtually unscathed. Now I’m ready to play professor to my constituents at T-Nation.

Being an aficionado of the nervous system and skeletal muscle link, I’ve analyzed tons of data pertaining to the effect the nervous system has on muscles. Even though this topic might seem to fall purely into the realms of academia, it has an important purpose for strength and hypertrophy-seeking individuals: knowledge.

If you don't further your training knowledge through science, your physique and performance improvements will stagnate. Therefore, this article will help clear up many of the questions you’ve probably pondered. At the end, I'll tell you how to apply this science to your training to achieve incredible size and strength gains.

Let the knowledge building begin!

Who’s in Control?

One of the more interesting questions addressed by physiologists was whether nerve controlled muscle, or muscle controlled nerve. In 1960, Buller et al designed an interesting study to answer this question. (1)

The Buller lab pulled a nerve out of fast muscle (flexor digitorum longus) and stuck it into a slow muscle (soleus). This process is known as cross-reinnervation. They measured isometric twitch contractions and relaxation times and found that the slow muscle became faster when innervated by a nerve that normally innervated fast muscle. (Say that three times fast!)

What did this mean? It meant that the nervous system could modulate skeletal muscle properties. In other words, nerve significantly controls muscle! Now you know why I make such a big to-do over the importance of understanding the nervous system for strength and hypertrophy seeking trainees.

Motor Units 101

A motor unit consists of a motor neuron and all the muscle fibers it innervates. There are three primary types of motor units: slow (S), fast fatigue-resistant (FFR), and fast-fatigable (FF). The muscle fibers within the motor units are particularly important since the contractile force of a motor unit depends on the force-generating capabilities of the muscle fiber type and the number of fibers innervated.

There are three types of muscle fibers to match the three motor units. They are: Slow Oxidative (Type I), Fast Oxidative Glycolytic (Type IIA), and Fast Glycolytic (Type IIB). There’s also a Type IIC muscle fiber type, but it’s usually a very small percentage of the total fiber count within a muscle.

Here’s a nifty little graph I put together for my presentation to give you a visual of motor units:

The bottom portion of the graph represents the force capabilities of the motor unit in response to repetitive stimuli. You’ll notice that the FG (Type IIB) fibers and motor units lose their force generating capabilities within one minute. This is one of the reasons why you can’t lift a near maximal load for any extended period of time. The FOG (Type IIA) fibers within the FFR motor unit also lose force capabilities within the first minute. Then, force begins to drop even further at the four minute mark.

As a strength physiologist, I’m primarily interested in FOG and FG fiber types when training for strength and hypertrophy since they have the most potential for growth (SO, Type I fibers exhibit minimal growth potential).

Size Matters

Around the same period of time as the Buller study, a Harvard physiology professor named Elwood Henneman performed a series of experiments to better understand how motor units are recruited. Henneman, along with a few other noted researchers, came to the conclusion that there’s an orderly recruitment of motor units during physical activity (2).

In other words, with low force activities, small motor units are activated first, with subsequent activation of larger motor units when greater levels of force are required. The greater the number of motor units recruited, the more hypertrophy and strength you’ll achieve. Here’s a graph to better illustrate this principle:

Turn your attention to the words "sprint" and "jump" at the top of the graph. Jumping and sprinting induce the greatest recruitment of fast-fatigable (FF) motor units. For example, when I train a client with the squat technique, I give him the instruction to "jump" the weight up. This is precisely the reason why I recommend super-fast concentric muscle actions for strength and hypertrophy — it leads to the greatest level of motor unit recruitment! Remember: more motor units = more hypertrophy (size).

The FF motor units are maximally recruited with:

What Causes a Muscle to be Slow or Fast?

For decades, researchers have scratched their heads wondering what in the hell makes a muscle become slow or fast in response to training. Even though factors such as contractile proteins, regulatory proteins, oxidative phosphorylation and glycolytic proteins have helped elucidate this issue, the question still remained.

For instance, it’s been well researched that muscle fiber changes occur in response to different training parameters (e.g. fast muscle fibers transform into slow, Type I muscle fibers in response to endurance training). (3,4) But the precise mechanism remained elusive. Well, inquiring minds, a model has been proposed to help clear up this foggy situation.

It appears that a few intracellular mechanisms are playing an important role in response to nerve activity. Low amplitude, long-duration activity caused by slow nerves and slow muscles appear to send a signal to calcineurin which, in turn, dephosphorylates a transcription factor named NFAT. Once dephosphorylated, NFAT can enter the nucleus of the muscle cell and activate the slow fiber program transcriptional machinery.

On the other hand, fast nerves and fast muscles don’t send the same signal to calcineurin. Therefore, NFAT remains phosphorylated and the fast fiber transcriptional program ensues.

I lost ya, didn't I? Here’s an illustration to help you understand the mechanism:

What Does All this Scientific Jargon Mean?

If you’ve made it this far, I’m very grateful. This science stuff ain’t for sissies! Now, I want to switch gears and talk specifically about resistance training for hypertrophy and the science of how it all works in concert.

Ultimate Training Parameters

If I was forced to perform one set of training parameters for the rest of my days, I’d choose the following method:

Much of the reasoning for my bias towards the 10 x 3 method is based on the previous scientific information. The aforementioned motor unit graph shows that the greatest force producing effects of the FFR and FF motor units occur within a timeframe of less than ten seconds. In fact, the shorter the set duration, the greater the potential for force production, if the concentric muscle action and load are high enough.

This is a very positive aspect of the 10 x 3 method: the sets are extremely short. Therefore, with large-load, low-rep training, high levels of force can be generated and maintained, unlike higher rep training where force (i.e. speed) greatly decreases as the end of the set approaches.

A second benefit to the 10 x 3 method is the relatively large load that can be used during each set. Remember, a large load (>80% of 1RM) will lead to rapid recruitment of the FF motor units which have huge growth potential.

But the most neglected aspect of hypertrophy/strength training that I observe is a lack of speed with the concentric muscle action (lifting the load). You must attempt to lift the load as fast as possible, even if the speed isn’t super-fast due to the large load that must be utilized.

The mere effort of lifting fast is enough to recruit those high-threshold (FF) motor units. This fast, tonic electrical stimulation to the muscles will keep that pesky NFAT from entering the nucleus and inducing slow-fiber program muscle fiber transcription.

In reference to the recommended rest periods, here’s what you should do. Try the 10 x 3 method with a compound exercise and utilize 60 second rest periods with a 5-6RM load. If your strength begins to drop off (i.e. you can’t perform all three reps) by the tenth set, increase the rest period by 30 seconds the next time you perform the workout (90 seconds).

Any rest period between 60-120 seconds will work, but each trainee will require a different rest period based on previous training and other neuromuscular issues.


Since this article is scientifically-based, I’ll reiterate how my presentation and the 10 x 3 method link together.

Benefits of 10 x 3 Method for Hypertrophy and Strength

Apply the Knowledge!

Now that I’ve given you the scientific basis for 10 x 3 training, I want you to follow through with the above guidelines. Pick a compound exercise for a body part that’s lagging (e.g. barbell squats for the thighs) and perform the 10 x 3 method at least once each week.

The other workout should consist of significantly different parameters in order to keep the nervous system as fresh as possible (e.g. 3 x 10 or 5 x 5). After a month, or so, contact me and let me know how it’s working for you.

Remember, if you seek training knowledge, hypertrophy and strength increases will follow!


1. Buller, A.J., J.C. Eccles, and R.M. Eccles. Interactions between motoneurons and muscles in respect of the characteristic of speeds of their responses. J. Physiol. (Lond.) 150: 417-430, 1960.

2. Henneman E., G. Somjen, and D.O. Carpenter. Functional significance of cell size in spinal motoneurons. J. Neurophysiol. 28:560-580, 1965.

3. Esbjörnsson M, Hellsten-Westing Y, Balsom PD, et al: Muscle fibre type changes with sprint training: Effect of training pattern. Acta Physiol Scand 149:245-6, 1993.

4. Andersen JL, Klitgaard H, Saltin B: Myosin heavy chain isoforms in single fibres from m. vastus lateralis of sprinters: Influence of Training. Acta Physiol Scand 151:135-42, 1994.


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