A whole lot of years ago, 82 to be exact, a neuroscience genius named Charles Sherrington was doing some innovative tinkering in his lab while studying reflexes. In the process of analyzing reflex inhibition, he came to the conclusion that the motor unit is the final common pathway of the motor system. (1)
Do you care? You should, because the key to getting stronger, bigger, faster, or any combination of the three depends on your understanding of how to recruit more motor units. In fact, if I had to sum up the intent and purpose of any effective size and strength training plan in one sentence, it would read like this:
Recruit as many motor units as possible with each muscle contraction.
An essential component to your training success depends on understanding that the force a muscle exerts depends on the amount of motor unit activity. This statement is supported by research as far back as 1929. (2) Train your body to develop more force and you'll get bigger, faster, and stronger. Of course, more force depends on recruiting more motor units – precisely why I keep hammering this point home.
Beyond that, it's important to perform enough contractions (or reps) in each workout to get the results you're after, but not so many that you induce excessive fatigue. That might sound simple enough, but it ain't simple – not by a long shot. So I'm here to address the first and most important issue: how do you recruit more motor units?
What I'm talking about is recruiting more motor units with every rep of every set.
I'm here to outline what research tells us about the adaptations that motor units undergo with different types of contractions. Keep in mind that a motor unit is basically the last link between what your brain has decided to do and what your muscles are about to do.
Hang tight with this discussion and I'll unveil the first installment of my latest training system for a stronger, bigger, and faster body!
Swimming in Motor Units
You've probably heard the term "motor unit pool" at one time or another. This pool is a collection of motor neurons in the spinal column that innervates a single muscle.
It's not so easy to visualize a motor unit pool. Even if you pulled out a butcher knife – one of them snazzy, infomercial doo-hickeys that cuts through an aluminum can – and hacked your spinal column up with your muscles intact, it'd still be hard because you'd need one helluva microscope to see what's going on. So I'm going to save you the trouble (and subsequent funeral arrangements) by dropping in this nifty picture.
There are two motor unit pools in the above picture: red and purple. Each color represents a different motor unit pool since each set of motor neurons innervates a different muscle.
For the sake of simplicity, let's focus on the red motor unit pool. See that red, spider-lookin' thing with the words "activation site" next to it? Each of those "spider legs" represents a branch of the motor neuron that receives input from the brain and spinal reflexes. This is the area of neural input that goes straight to the muscle.
So the key is to activate this site as much as possible to get your muscles to produce as much force as possible. How? Let me explain.
Motor Unit Recruitment and Rate Coding
There are two primary mechanisms the nervous system uses to augment muscle force: motor unit recruitment and rate coding. For most muscle groups, approximately 85% of maximum force comes from recruiting more motor units. (3) The remaining force production comes entirely from a process called rate coding.
Importantly, this force-producing information comes straight from your brain. You can't see it in the picture, but imagine a line of electrical input that runs from your brain down to the little red "spider" in your spinal column.
Motor unit recruitment is just like it sounds: the nervous system recruits more muscle fibers by activating more motor neurons, and at a faster pace. I like to focus my lectures on motor unit recruitment because it's the process that science knows the most about.
Plus, it constitutes the greatest percentage of our force capabilities. And there's little doubt that we can greatly enhance our ability to recruit more motor units – and recruit them quicker – with training.
Once the recruitable muscle fiber pool is maxed out, the nervous system speeds up the signal (neuronal input) to the muscles from rate coding. Think of rate coding as an SOS distress signal from your brain down to the motor neurons in your spinal column. The more signals that are received at the motor neuron, the greater the "emergency." This is how our peak levels of max strength are achieved.
I was once asked an excellent question by one of the top coaches in the country, "Can we train rate coding?" In other words, can rate coding be enhanced with training?
That is one loaded question, my friends! There's so much conflicting research on rate coding that I'd be doing you a disservice if I spent too much time discussing it.
Intuitively, it seems that rate coding is what's really enhanced during life-or-death situations when superhuman strength feats have been witnessed. But I'd be hard-pressed to say that it can't be enhanced with training.
Speed and Motor Unit Recruitment
As of late, I've been doing a lot of hand waving about the importance of fast contractions. The reason is simple: research supports fast contractions for maximal motor unit recruitment.
But you just want bigger muscles, right? Well, to get bigger muscles you need more strength, and to get more strength you need to train your nervous system to recruit more motor units. So that's why I extrapolate the information from strength training research and apply it to muscle-building programs.
Elite athletes typically have a big advantage over weekend warriors because the former can recruit their largest, most powerful motor units quicker than a non-athlete. This makes sense given that the purpose of training is to increase performance.
One of the nervous system enhancements that come from training is to recruit the majority of your motor units more quickly. This is the reason why an Olympic level weightlifter can produce maximum force during the first rep while a weekend warrior might need an extra rep to do the same.
- "Why should I train with fast contractions?"
- "Why should I try to lift a heavy barbell as fast as possible?"
The reason why you should perform fast contractions is because it reduces the recruitment threshold of motor units. (4) What in the hell does that mean, you ask?
For the sake of simplicity, let's say you have 100 motor units that work to curl a barbell. To produce maximum force you must recruit all 100 of those motor units as fast as possible. After all, the whole purpose of lifting is to overcome the resistance of the barbell, right?
When you train with ballistic contractions, your nervous system reduces the recruitment threshold of the motor units. In essence, this reduction in recruitment threshold allows you to recruit your muscle fibers more quickly.
Put another way: fast contractions make your muscles faster by recruiting the motor units more quickly. Your time to peak force is known as the rate of force development (RFD). The shorter your RFD, the more force you'll be able to produce in less time, otherwise known as explosive strength.
Maybe you don't care about becoming as explosive as an athlete by training with ballistic contractions. Well, this information is still applicable. Not only will fast contractions enhance your ability to recruit motor units more quickly, but also your ability to recruit more motor units. (4)
Remember what I said about the importance of recruiting more motor units? It should be the ultimate goal of any size and strength-building program. And the aforementioned research demonstrates that if we train with ballistic contractions, instead of slow contractions, we'll recruit more motor units. That's exciting!
This info is also applicable to light loads. After all, the research in question used a protocol with 33% of max to elicit the enhanced motor unit recruitment response. But the research only looked at training dorsiflexion (anterior tibialis muscles). It stands to reason that the loading protocol might need to be altered for more complex movements like the squat or deadlift. Nevertheless, you don't need to train heavy all of the time to build bigger, stronger, faster muscles.
Applicability for Training with Light Loads
Training with light loads and fast contractions goes under many different names such as speed strength training or the dynamic effort method. Regardless of the name you choose, it's a great way to train, some of the time. As a gross generalization, I like to spend at least one workout each week with lighter loads and lightning fast tempos.
So how should you apply this information to your own training plan? There are many different protocols that prescribe a specific rep range with light loads. For the sake of this discussion, I'll say that any load that's less than 60% of your 1RM is considered a light load.
A.S. Prilepin devised a table that recommends a specific rep range for various loads. It's revered by powerlifters and strength athletes, as it should be. It's a great starting point for any avid lifter. (If you don't own Managing the Training of Weightlifters, pick up a copy.)
What I like about Prilepin's chart is that it's basically in line with my latest training system. Indeed, his rep protocol is based on performing a certain range of reps before the speed slows down. He noted that as the speed of a movement decreases, so does the power production. That's nothing new, but it bears repeating.
What is new, however, is something that I'm bringing to the forefront of the fitness community: once the speed slows down, it's time to terminate the set because, I believe, you're recruiting fewer motor units. (If that last sentence leaves you befuddled, check out this article.)
However, I've found that the Prilepin table isn't as applicable to the avid weekend warrior as it could be. That's not to say that there's any flaw in his table, but his information was based on Olympic lifters while my new system is for all people who want to increase their performance and muscle mass. This is the point where my protocol takes a tangent from Prilepin's guidelines. The answer to the puzzle is much simpler than calculating a specific percentage of your one repetition maximum (1RM) and subsequently adhering to a certain set and rep range.
I've come to the realization that I've been too hung up on specific training loads over the years. It's frustrated a lot of people because it ain't easy to calculate a specific percentage of 1RM for any given lift. Furthermore, take two guys and each will perform a different number of reps with the same percentage of 1RM.
For example, one guy might be able to perform 12 reps with 50% of 1RM before the speed slows down. Another guy might only get eight reps with the same percentage before the speed slows down. So it's unnecessary to prescribe a certain rep range with a specific load because it doesn't take into account all of the different conditioning levels that make up the fitness spectrum.
Make no mistake about it: this is a novel approach to training for size and strength. This isn't speed strength training and it's not the dynamic effort method. Both of those methods are based on performing a specific number of reps with a specific load. Furthermore, those methods are solely intended to build speed strength.
My new method, however, doesn't prescribe a specific load and it isn't limited to any specific rep range. You might be able to perform, say, five more reps with a given load than your buddy before the movement slows down. In essence, my new approach to training is customized to every person: choose a load and lift it as fast as possible, for as many reps as possible. Once the speed slows down, terminate the set. Finally, the goal of these workouts is to enhance your ability to build bigger, stronger muscles.
I customize my approach by focusing solely on the speed of the movement with any load. Here's what I want you to do for one workout each week for the next month:
- Pick any three compound movements. The first movement should be an upper body pulling, the second is an upper body pushing, the third is a squat or deadlift variation.
- Choose a light load that you could lift 20-25 times before failure. No need to test this if you've been training for any length of time, just guesstimate because there's no such thing as a perfect training load. Any light training load will do the trick.
- Perform both the shortening (concentric) and lengthening (eccentric) phases as fast as possible while maintaining perfect form and control. In other words, just because the eccentric phase should be fast doesn't mean you should just drop the load. Control it.
- Use the same load for all sets and terminate the set as soon as the speed slows down.
- Use the following total body circuit as your workout structure: upper body pulling, rest 60 seconds, upper body pushing, rest 60 seconds, squat or deadlift, rest 60 seconds and repeat the circuit four more times.
- Increase the load of all movements by five pounds with each new workout (week). So by week 4 you'll be training with 15 pounds more than you started.
- Perform a total body training session at least three times each week. I've outlined how one of the workouts should be designed. Your job is to train with heavier loads for the other two workouts each week. But be sure to terminate your heavier sets as soon as the speed slows down.
Here are three sample workouts:
Fast to Big Workout 1
A1 Lat pulldown
A3 Romanian deadlift
Rest 60s and repeat four more times
Fast to Big Workout 2
A1 Seated cable row
A2 Standing military press
A3 Back squat
Rest 60s and repeat four more times
Fast to Big Workout 3
A1 Chest supported row
Rest 60s and repeat four more times
You can choose any movements you want for the Fast to Big workouts. The key is to find three that you like and stick with them for one workout each week for four weeks. As mentioned, the other workouts should consist of different movements with heavier loads.
There are six unique training protocols that I've designed for my new training system, and they all incorporate different loads, workout structures, and methods. This is the first method and it incorporates light loads.
The reason why I chose to unveil this method first is because most people need to improve their rate of force development. By doing so, you'll enhance your ability to recruit motor units at a faster pace. That's important because it'll lead to a stronger, bigger, faster body by supercharging your rate of motor unit recruitment.
The other reason I chose this installment first is because this method is going to seem most familiar to those who've been in the weight training game. So, I'm going to ease you into my new plan.
But the real novelty in my latest system is how I manipulate the training variables with heavier loads. It's not easy to perform more than a few reps with a maximal load before the speed slows down, but I've found a way. Scratch that, I've found two ways. I've also discovered three other ways to get the same effect with medium and light loads. What are they? You'll have to wait and see.
So, for now, experiment with the above plan and you'll be one step closer to the entire system I've designed!
- Sherrington, C. Proc R Soc Lond B Biol Sci B97: 19-45, 1925.
- Adrian E and Bronk D. J Physiol 204: 231-257, 1929.
- Van Cutsem, et al. Can J Appl Physiol 22: 585-597, 1997.
- Desmedt JE and Godaux E. J Physiol 264: 673-693, 1977.