The Central Nervous System is involved in all movement, with sophisticated communication via electrical signal from the brain, through the spine, down into the nerves that break off into motor units (motor neuron axonal terminals that control the muscle fibers). The purpose in training the CNS is to increase this efficiency. Understanding how to train and how to support these adaptations with both cardiovascular and strength training will ultimately result in increased human performance.
I am not a neurological doctor nor do I have direct access to the original laboratory findings; therefore, I am not qualified to diagnose or treat any neurological problems. This article is not intended to replace a medical visit. This article is a discussion on the training adaptations that occur within the CNS and how to solicit adaptations intentionally and safely based on real world experience and various published journal findings.
The motor unit refers to the motor neuron and the muscle fibers within its span of control. The ratio between motor neurons and muscle fibers varies. For example, in the quadricep, one motor unit may include a single motor neuron that is responsible for voluntary contraction of thousands of muscle fibers. A group of motor units is known as a motor pool, and motor pools are what relay voluntary contraction to the muscle groups as a whole. Coordination between the motor pool of the agonist (primary mover) and the motor pool of the antagonist (stabilizing muscles) result in a coordinated movement.
The brain sends the signal to the motor units within the motor pools of the target muscle groups to initiate movement, and depending on intensity of the movement may lead to either a submaximal voluntary activation (SVA) of the motor units or a maximal voluntary activation (MVA) of the motor units. Furthermore, depending on the intensity of the movement, either most (85-95%) motor units within the motor pool will be activated (full), or only some of the motor units within the motor pool will be activated (partial). For example, squatting down to pick up the newspaper will elicit the partial SVA of the motor units available; however, a 1RM squat will require a full MVA of the motor units available. During a set of 8-12 reps to MMF, there will be a variable activation throughout the set, where the first few reps may only elicit a partial SVA, but as the intensity of the movement increases with fatigue, additional motor units will be activated until there is a full MVA within the motor pool during MMF.
All movement requires at least a partial SVA and can lead to neural adaptations with training; however, full MVA leads to the best gains in neural adaptations and increases in human performance. The training modalities that can solicit full MVA include Olympic lifts, 1RM, sprints, plyometrics, and strength training to MMF at any rep range. All of these share the same core foundation of being large, dynamic, explosive movements. There are pros and cons to each modality, mainly relating to the risk-to-benefit of each modality as well as the impact of fatigue and strain placed on the musculoskeletal and cardiovascular systems. Make sure to read the section on practical considerations before implementing any modality into your training regimen.
The primary neural adaptation that affects human performance is the increase of peak force production during MVA, which is the result of the combination of improved motor unit activation, increased percentage of motor pool activation, signal discharge rate, and coordination between motor pools. As the peak force during MVA increases, performance during partial SVA also improves, allowing for fewer motor units to be required to do the same tasks, with less activation required within the same motor units.
- IMPROVED MOTOR UNIT ACTIVATION: As the individual motor units within the motor pools are activated during training sessions, over time they become more efficient at the activation process. This is why during the first few weeks of a new strength program, performance increases can occur without gaining muscle. Improved motor unit activation contributes to an increased peak force production.
- INCREASED PERCENTAGE OF MOTOR POOL ACTIVATED: Without pushing the body to full MVA, many motor units are rarely used. Training to full MVA will cause the activation of these reserve motor units, resulting in a greater percentage of motor units activated within the motor pool. Training to full MVA over time causes these reserve motor units to improve in activation, leading to increased peak force production.
- SIGNAL DISCHARGE RATE: Another neural adaptation is the speed at which the signal can travel between the brain and the motor units. It may only increase by a few milliseconds, but a faster activation signal results in increased human performance. When combined with all other training adaptations, an increased signal discharge rate also contributes to an increase in peak force production.
- COORDINATION BETWEEN MOTOR POOLS: This is usually referred to as “muscle memory,” or the ability for the coordinated effort of several muscles groups and all associated motor pools to activate in harmony, from partial SVA up to full MVA. Training results in an improved coordination between motor pools of all activated muscles, and this coordination improvement contributes to an increase in peak force production.
While the focus of this article is the neural adaptions of a variety of training modalities that all solicit increases in peak force production, the reality is that the CNS is not trained in a bubble. Other body systems are in play. The musculoskeletal and cardiovascular systems in particular are involved in each of the training modalities that excel at soliciting neural adaptations. The limitations in these systems will be what holds back neural adaptations, not the central nervous system.
- MUSCULOSKELETAL SYSTEM: A basic, balanced, comprehensive strength training program is a prerequisite for a program that intentionally pursues full MVA. It is not safe or productive to attempt Olympic lifts, plyometrics, full speed sprints, 1RM, or strength training to MMF without a foundation of a strong musculoskeletal system. The foundation in strength training will solicit improved motor unit activation and coordination between motor pools at partial SVA, the stepping stones toward full MVA.
- CARDIOVASCULAR SYSTEM: A consistent conditioning program geared towards ATP-CP and LA systems is a prerequisite for full MVA programs, particularly those utilizing sprint and plyometric modalities. It will not be effective to attempt sprints at maximum speeds for the purpose of improving peak force production if one or two sprints leads to being out of breath and fatigued. Running slowly will not make you faster, running fast makes you faster. Same thing applies to plyometrics. A consistent conditioning program is a prerequisite for more advanced plyometric programs geared towards neural adaptations from full MVA.
Explosive, dynamic movements like speed and agility training, plyometrics, 1RM or Olympic lifts, should not be performed when fatigued. The goal of each of these modalities is to tap into the maximum amount of motor units. In order to do that, the cardiovascular and musculoskeletal systems need to be in a rested state in order for them to give their best effort. So how much rest is needed to be 100% with heart, lungs, muscles and bones to give it a go on a movement or drill that will tax the CNS? When should we target the CNS system in a workout?
- 1:30 – As a starting point, however long it takes you to complete a movement/dill, give yourself 30x that amount as rest. For example, if it takes me 5 seconds to complete a movement/drill, than I should give myself 2.5 minutes to rest before attempting the same movement or another similar movement. If you need more time to calm down and get your mind right, take more time. Quality is king with CNS training.
- EARLY OR ISOLATED: In my experience, CNS training programs should either be incorporated at the very beginning of other workouts, or isolated entirely. Three sets of power cleans can be performed with a 1:30 rest ratio before your traditional strength program. Same goes for plyometrics or speed training, do them at the beginning of a conditioning workout, when you are fresh. Another option is to isolate them entirely. You will absolutely be resting more than you are working. In an hour workout, only 2 minutes of actual work will be completed if you follow the 1:30. All CNS training is short and intense, typically lasting less than 5 seconds.
No matter how strong or conditioned you are, the cardiovascular and musculoskeletal systems will always “fail” before the central nervous system; however, in order to solicit neural adaptations, it is best to intentionally approach the workouts, sets, and exercises fresh. Cross-training modalities that attempt to cause both musculoskeletal and cardiovascular fatigue while placing demands on the central nervous system are not only dangerous, but less effective at promoting adaptations in peak force production than protocols that allow for more time to rest. From a rested state, attacking a set of plyometrics, sprints, Olympic lifts, or a 1RM will safely allow for full MVA and will ultimately produce more neural adaptations than performing the same movements in a fatigued state.
We are born with a genetic makeup of motor units that we can either train to its full potential or allow to remain dormant. Unfortunately we do not have the ability through training to increase the amount of motor units in our bodies or increase our neural network. What we can do is make sure we are tapping into as many of our God-given motor units as possible, and improve their capacity for activation, percentage of available utilized, signal discharge rate, and coordination between motor pools. Additionally, the percentage of motor units activated during partial SVA seems during a large movement like a deadlift may be 65% for example, and with training can tap into close to 95%. At no point will out body allow for 100% activation, we are wired to always have a little left in the tank.
Nick Ryan, CSCS
Journal of Applied Physiology,
Journal of Sports Medicine
European Journal of Applied Physiology