As lifters, we tend to just think about muscle and strength. But if we really want to lift heavier, we need to start thinking about the neuromuscular system.
The neuromuscular system is the integration of your nervous and muscular systems to perform movement. Without an optimal neuromuscular system, we're not able to display maximal strength. We already know about the "muscular" part of that word because we know bigger muscles are capable of producing more force... emphasis on the word "capable."
But we very rarely train with the "neuro" part of that word in mind. By ignoring it, we ignore half the equation that allows us to display maximal strength.
Have you ever wondered how a person who weighs less than 200 pounds is capable of squatting 600, 700, or even 800 pounds? The answer is simple. They don't have more muscle than a 300-pound monster, but they're better at getting what they DO have to work together to produce a maximal contraction.
This ability allows them to display their strength more effectively, so they get more out of less. That display of strength is driven by the neuro part of this system, not the muscular part.
There are four main factors that affect your neurological system's ability to display strength:
- Motor unit recruitment
- Motor unit synchronization
- Neuromuscular inhibition
- Rate coding
Are these trainable? Let's find out.
One singular muscle is made up of thousands, if not millions, of muscle fibers. Each individual fiber is innervated by a motor neuron, which often controls more than one muscle fiber (usually 10 to 1000 muscle fibers are controlled by one motor neuron).
A motor neuron and all the fibers it controls are referred to as one motor unit. When that motor unit receives the signal to contract, all the fibers within that motor unit contract.
Here's where the problem comes in: the rectus femoris muscle is controlled by something to the tune of 1000 different motor units, and a maximal contraction requires getting them all contracting at one time, which isn't easy to do.
The human body has two basic types of muscle fibers: type I and type II. (Yes, we can break them down further, but it doesn't benefit this discussion.)
- Type I fibers are considered slow-twitch, aerobic, low-force producing fibers.
- Type II are your fast-twitch, anaerobic, high-force production fibers.
Logic dictates that the higher number of type II fibers we can recruit, the more strength we can display. Seems simple, right? Recruit more type II fibers, produce greater force, move more weight, jump higher, run faster, etc. But there's a problem.
In 1965, a group of researchers led by Elwood Henneman figured out that type I fibers have lower recruitment thresholds than type II fibers (1). This means they're recruited before type II fibers during any type of muscular work.
Recruitment takes time, so producing maximal force rapidly is a tall task, but there are ways to work at it. Step one is to teach your body to activate those type II fibers, which requires strain and time under tension.
Electromyography data shows us the "slow build" of motor unit recruitment in contractions, which look like this:
Here you see that from the onset of contraction to the first peak of motor unit recruitment is nearly an entire second, and the absolute peak of this motor unit recruitment doesn't occur until nearly three seconds into this isometric contraction.
Well, waiting for three seconds to produce maximal force is rarely going to help us display our strength maximally (powerlifting is the exception to that rule).
So the question arises, can we train ourselves to recruit type II fibers more quickly? The answer is yes... and also no.
Ideally, we'd be able to reverse the order of recruitment so that we could activate the type II (fast-twitch) fibers before the type I (slow-twitch) fibers, but there's little evidence suggesting this is a possibility. The human body seems to regard that as trying to walk before you crawl.
However, there's some evidence that light load ballistic training is capable of increasing the rate of type II fiber recruitment by lowering the recruitment threshold for type II fibers (2).
Think about it. There's a reason why Westside Barbell has produced some of the strongest lifters in the world: their system trains both of these mechanisms.
Basically, with the conjugate method, there are two training days: max effort and dynamic effort. Max effort day is all about straining, meaning you spend 3-4 seconds (or more) to complete a rep. Looking up at the graph, that seems a lot like the isometric contractions, which get us maximal motor unit recruitment.
Dynamic effort day is then about moving weight in a ballistic fashion, training your body to lower those recruitment thresholds and reach peak force sooner.
The bottom line? You need to strain sometimes in your training. The load needs to be heavy and over 90% of your max. Similarly, sometimes you need to move fast; somewhere between 40-60% of your max should do the trick.
Training both ends of the spectrum will enhance your ability to recruit your type II muscle fibers and display your maximal strength.
Motor unit synchronization is a fancy way to say multiple motor units firing at the same time to produce a maximal contraction. Most muscles in the body are controlled by more than one motor unit, so if we want to get the most out of the muscle as a whole, we need all the motor units firing together.
There's plenty of evidence showing resistance training will increase motor unit synchronization (3, 4), but the scientific literature doesn't do much to explore what specific type of resistance training may be best.
However, most of us would agree that when we first teach or learn movements, we apply a "slow and steady wins the race" mentality, allowing us to learn the movement. As we progress, the deviation from perfect form should be consistently reduced, meaning our motor unit synchronization is getting better.
Another great example is bodybuilding or any physique-style posing. The goal is to be able to create maximal tension and display the largest, most symmetrical build you can. Doing this requires all of the motor units in a given muscle to fire simultaneously. How do most bodybuilders learn this skill? Slow, controlled, timed repetitions and a lot of time under tension.
Now, if your goal is to display maximal strength, don't you think learning that skill may come in handy? So occasionally, train like a bodybuilder at slow tempos. Spend some training blocks exploring the contraction and feeling the muscle. You might even consider taking a posing lesson or two.
Neuromuscular inhibition refers to the reduction in motor unit recruitment during a muscle contraction. Why does this happen? Well, frankly, God only knows at this point. Science has postulated it has to do with neural feedback from joint, muscle, and tendon receptors like Golgi tendon organs, but the exact mechanisms remain somewhat a mystery.
Of course, we don't want to inhibit motor unit recruitment when we're trying to display our maximal strength. Some good news here: heavy resistance training does seem to diminish the amount of neuromuscular inhibition we experience (4); however, once again, scientific literature in this area is lacking.
That said, we're fairly certain this inhibition occurs as a result of the body trying to protect itself from injury. So we need to train our body to override its instincts and accept heavy weight without trying to save itself.
The best? Heavy rack holds. It's simple and effective. If you squat 405, put 465 on the bar, stand up, and hold it for several seconds, then return it to the rack. This technique will train your neurological system to accept this weight as part of its job, preventing it from inhibiting your display of strength in a full squat.
Rate coding is the final neurological factor that helps you display your strength. In a nutshell, this is referring to how often or how fast the signal for a motor unit to contract occurs. The faster this happens, the greater force a whole muscle is able to produce.
There's evidence that resistance training of pretty much any kind can help to increase rate coding (2, 5). However, the question is not will resistance training work; the question is, what type of resistance training is best?
Well, in terms of rate coding, the fastest movements are going to produce the greatest results. We need our motor units to fire early and often to display our maximal strength, so anything allowing us to accelerate rapidly will be the most optimal.
Olympic weightlifting variations, lighter loads lifted faster (like for squats), and plyometrics are all great choices. A good sprint program would also do the trick.
As you were reading this, you should've noticed something: almost all of these neurological factors that affect your ability to display strength require one of two things: either super-heavy loads at a slow pace (or no pace in terms of the heavy rack holds) or ballistic, fast movements at light loads.
These two things may occur at the opposite ends of the training spectrum, but that doesn't mean they aren't both important. It just means you need to program your training accordingly and avoid that murky middle of 8 reps at 80% if displaying maximal strength is the goal.
- Henneman, E., Somjen, G., & Carpenter, D. O. (1965). Functional significance of cell size in spinal motoneurons. Journal of neurophysiology, 28(3), 560-580.
- Van Cutsem, M., Duchateau, J., & Hainaut, K. (1998). Changes in single motor unit behaviour contribute to the increase in contraction speed after dynamic training in humans. The Journal of physiology, 513(1), 295-305.
- Suchomel, T. J., Nimphius, S., Bellon, C. R., & Stone, M. H. (2018). The importance of muscular strength: training considerations. Sports medicine, 48(4), 765-785.
- Aagaard, P., Simonsen, E. B., Andersen, J. L., Magnusson, S. P., Halkjaer-Kristensen, J., & Dyhre-Poulsen, P. (2000). Neural inhibition during maximal eccentric and concentric quadriceps contraction: effects of resistance training. Journal of Applied Physiology, 89(6), 2249-2257.
- Del Vecchio, A., Casolo, A., Negro, F., Scorcelletti, M., Bazzucchi, I., Enoka, R., Felici, F., & Farina, D. (2019). The increase in muscle force after 4 weeks of strength training is mediated by adaptations in motor unit recruitment and rate coding. The Journal of physiology, 597(7), 1873–1887.
EMG Chart Credit: All Answers Ltd. (November 2018). EMG Activity Force Production in an Isometric Contraction.