WHO'S IN CONTROL?
One question addressed by physiologists is whether nerve controlled muscle, or muscle controlled nerve. Researchers sought to find the answer in 1960.

The scientists pulled a nerve out of fast muscle (flexor digitorum longus) and stuck it into a slow muscle (soleus); a process called 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.

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 the importance of understanding the nervous system for strength and hypertrophy.


Motor Units 101
A motor unit consists of a motor neuron and all the muscle fibers it innervates.


Motor Unit
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.

AN EVEN CLOSER LOOK
Diagram 1
The bottom portion of this diagram 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. Notice that Type I fibers exhibit minimal growth potential.


Size Matters
A Harvard physiology professor performed a series of experiments to better understand how motor units are recruited. He and his fellow researchers came to the conclusion that there's an orderly recruitment of motor units during physical activity.


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.

This diagram illustrates the principle:

Diagram 2
Notice the words "sprint" and "jump" at the top of the diagram. Jumping and sprinting induce the greatest recruitment of fast-fatigable (FF) motor units. For example, when I train an athlete 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:

High load training: > 80% of 1RM
Super-fast concentric muscle actions (lifting the weight quickly)
Achieving muscular failure utilizing a submaximal load


Ultimate Training Parameters
If you could only choose one set of training parameters for the rest of your life what would you do? Here's what I'd do:


Sets: 10
Reps: 3
Load: 80-85% of 1RM, or 5-6 RM (Repetition Maximum)
Rest: 60-120 seconds between sets
Tempo: 20X (lower weight to a count of two, no pause, lift as fast as possible)
Exercise: Any compound movement
My bias towards the 10 x 3 method is based on science. The motor unit graph above shows that the greatest force producing effects of the FFR and FF motor units occur within a timeframe of less than ten seconds.

The shorter the set duration, the greater the potential for force production, if the concentric muscle action and load are high enough.

With 10 x 3 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 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 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 and 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 lifter will require a different rest period based on previous training and other neuromuscular issues.


Four Benefits of 10 x 3
10 x 3 training utilizes a large load (>80% of 1RM). This load is necessary to recruit the FF and FFR motor units that possess FG Type IIB and FOG Type IIA muscle fibers, respectively. This is very important since the aforementioned fibers have the greatest potential for growth.
Super-fast concentric muscle action (lifting) during the set maximally recruits the motor units mentioned above.
With only three reps per set, the total duration of the set is very short (~9 seconds). This is imperative since the force producing capabilities of the FFR and FF motor units decrease at any time longer than approximately 10 seconds.
Fast, tonic stimulation of the FFR and FF nerves doesn't cause dephosphorylation of NFAT. Therefore, fast fiber program transcription ensues (i.e., you won't transform your precious Type IIB and Type IIA fibers into puny Type I fibers).

Application
Now that you know why 10 x 3 training works, try it. Pick a compound exercise for a body part that's lagging (like barbell squats for the quads) and perform the 10 x 3 method at least once each week.

The other parts of your workout should consist of significantly different parameters in order to keep the nervous system as fresh as possible (like 3 x 10 or 5 x 5). Then give it a month.

Seek training knowledge and the gains will follow.


References
Buller AJ et al. Interactions between motoneurons and muscles in respect of the characteristic of speeds of their responses. J Physiol. 1960 Feb;150(2):417-39.
Henneman E et al. Functional significance of cell size in spinal motoneurons. J Neurophysiol. 1965 May;28:560-80.
Esbjörnsson M et al: Muscle fibre type changes with sprint training: Effect of training pattern. Acta Physiol Scand. 1993 Oct;149(2):245-6.
Andersen JL et al. Myosin heavy chain isoforms in single fibres from m. vastus lateralis of sprinters: Influence of Training. Acta Physiol Scand. 1994 Jun;151(2):135-42.

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