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Neural Plasticity and Strength Training

When it comes to strength training it’s really common to hear people refer to ”Neurological Strength” or ”Neural Drive” when discussing the importance of the the neurological system in strength. This statement has a lot of basis but unfortunately the majority of people that mention it can’t really go much deeper than saying ”Yeah, it’s really important.” What is actually happening when we talk about neurological adaptations to strength training is a couple of different forms of neural plasticity; primarily the reorganization of the motor cortex, via cortical synaptogenesis for skill development, and spinal synaptogenesis (synaptogenesis = creation of new synapses between neurons) in direct response to strength training (Adkins, 1985, Swain et al, 2012). The specifics of these terms is not important for the purpose of this article, just know that the motor cortex acts like a switchboard operator when it comes to determining which motor neurons need to fire.

You may be wondering what does the nervous system have to do with strength anyways? Isn’t it all about muscle size? Well no, not at all. You see muscles have one really simple action they perform; contraction. Muscles contract in response to the electrical stimulus they receive from their associated motor neurons. So while it is true that bigger muscles can produce more contractile force, they can’t produce that force at all without the “Go” signal from the nervous system. So now we have a very simple framework to understand how the nervous system plays a role in strength training.

 

Next, consider the first time you ever tried to bench press. Chances are you looked, and were, pretty awkward. This is because even though you may have known which muscles to use, you didn’t really know the how or when that comes with experience. Basically you grabbed that weight, lowered it to your chest, and then fired every motor neuron connected to your chest, triceps, and shoulders to try to launch it. Over time you, hopefully, learned how to bench with a little more finesse, and now you press the weight off of your chest by first contracting with your chest and finish with a strong tricep contraction. The experience that fed into learning this better sequence also worked to reorganize the motor cortex to encode for an optimal set of sequences to fire the motor neurons used to bench the weight.

Now that we have a general framework and a simple example of how neural plasticity and strength training work together let’s get into the details.

Behavioral Drivers of Neural Plasticity

According to Kleim (2012)* the behavioral drivers of neural plasticity are:

  • Repetition
  • Intensity
  • Timing (Coordination)
  • Difficulty
  • Specificity
  • Salience

In the following video I talk about each of these behavioral drivers and how they relate to strength gains:

 

While the wording may be somewhat different, these factors are something that strength coaches everywhere have known for a long time. Essentially, to stimulate an adaptation to something (like lifting heavy weights) the stimulus needs to reoccur frequently (repetition), has to take significant concentration (intensity), be at a sufficient difficulty to require adaptation, and must be important to the individual (salience). Timing, or coordination, refers to what is best described by the adage of “Neurons that fire together, wire together,” often called “Hebbian Learning.” Lastly, specificity refers to the fact that the action that we are adapting to must be specific.

Let’s now revisit our previous example of training the bench press and compare it to each of these factors:

  • Repetition – Bench pressing 1-2x per week
  • Intensity – Regularly benching 80-95% of your 1RM
  • Timing – Ensuring your form is on point and muscles move in a coordinated fashion
  • Difficulty – Continually trying to incrementally increase performance
  • Specificity – Benching more will make it so you can bench more, but not so that you can run more efficiently
  • Salience – “Benching is important to me because it will get me the strength I want!”

Using these factors to structure your training

As you can see these behavioral factors are very similar to the metrics we commonly manipulate in the gym to improve performance. Most commonly, the metrics we manipulate are Repetition, Intensity, and Difficulty. These are the most important factors to manipulate for experienced lifters. In fact, it is advisable to try to optimize your gains by rotating which of these factors you emphasize. For example competitive powerlifters will often employ a high volume training strategy (High repetition factor) for a length of time and then go into a ’taper’ period in which they systematically decrease the volume and increase the weight (High intensity factor), resulting in an overall better performance at their competition. This kind of plasticity is a direct result of spinal synaptogensis; the creation of new synapses in the nerves extending from the spinal cord into the muscles. Essentially, this creates a more powerful driver for muscle contraction.

However, when you are first learning a new lift/movement it’s smart to focus on the repetition and timing factor above all else. Keep intensity and difficulty low so that you can do the movement frequently and do your best to keep your form on point. These early days are when you are actively reorganizing the motor cortex to learn how to perform the movement. In these early times of learning a movement you are engraining the foundational neural pathway for that movement, so if you build good form now you don’t have to go back to fix it later. If you build your foundation with shitty form it’s extremely difficult to back and fix it because you’re not just learning good form, you have to forget bad form (which is another entire plasticity article in itself).

Summary

When it comes to Neural Strength in strength training we are talking about neural plasticity applied to strength. When we first learn a new movement the predominant form of plasticity is motor cortex reorganization and it is literally our brain learning the optimal set of sequences for firing the various nerves controlling the muscles to control the movement. Later on, the motor cortex does not see as dramatic of a reorganization, instead the predominant form of plasticity becomes spinal synaptogenesis; an increase in the number of synapses in the motor neurons controlling the muscles. This essentially creates a more powerful driver to the connected muscles stimulating more powerful muscular contraction.


*This reference is a textbook.