man leaning on barbell with weights on it in gym

Have you ever found yourself lying in bed after a hard training session and feeling tired but unable to fall asleep?

Or maybe you just finished a workout and now feel unmotivated and unable to focus?

The theory is, CNS fatigue is responsible for that.

But is that true, or maybe these adverse effects result from something else? Let’s discuss.

What Is Central Nervous System Fatigue?
The central nervous system consists of two things: the brain and the spinal cord. Your brain is the central processing unit inside your body. It interprets the environment, sends commands, oversees processes, and receives input from your body. Your spinal cord is the nerve column that runs from the brain to the base of your back.

The theory is, central nervous system fatigue is the state in which your brain can’t (or doesn’t want to) pass commands to your body. In the case of training, this would refer to your ability and readiness to do hard work. If you’re experiencing CNS fatigue, your brain doesn’t send strong signals to your muscles, which prevents you from producing powerful contractions and exerting enough force. In simpler terms, you feel weaker, less explosive, and less endurant.

Central nervous system fatigue can also be independent of peripheral fatigue. For example, a specific muscle in your body might be perfectly rested. But it might fail to contract as strongly as it can due to poor CNS signaling.

What Causes CNS Fatigue (And What Happens Inside The Body)?
Physical exertion is a good way to fatigue your central nervous system. But contrary to what people believe, low-intensity prolonged exercise appears to cause the most CNS fatigue. In contrast, short-duration, high-intensity exercise seems much more forgiving, even in elite athletes. One potential reason is that low-intensity exercise forces continual effort, where more intense activities are typically interspersed with rest periods.

Another way to fatigue the central nervous system would be to exert more effort. In other words, pushing yourself closer to failure can cause greater peripheral and central nervous system fatigue.

Interestingly, some research shows that even significant CNS fatigue can go away within… minutes. So, we could speculate that what most people deem as CNS fatigue is actually peripheral fatigue, and the nervous system downregulates activity to keep the body from hurting itself through severe physical exertion.

Still, we need more research before making claims on that front.

What Can We Do To Avoid CNS Fatigue?
According to research, CNS fatigue isn’t as bad as some people believe. Still, here are a few things we can do:

  • Limit low-intensity prolonged exercise, such as jogging, especially if you primarily care about building muscle and strength. As we saw from research above, this type of exercise seems to cause more CNS fatigue than short and more intense activities.

  • Take regular deload weeks to give your body more time to repair the damage. Typically, you should aim for a whole week of light training every six to eight weeks of challenging workouts.

  • Organise your weekly training, so you feel recovered enough for each upcoming session. Stress is cumulative, and doing too much can lead to overtraining.

  • While sometimes beneficial, you should mostly stay away from training to failure. As a rule, leave a repetition or two in the tank. Don’t worry; this is still serious and challenging training.
September 13, 2021 — Daniel Felstein

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