Majority already knows that CNS (central nervous system) is contained of brain and spinal cord and that it controls a number of body functions, one of which is muscle contraction. At first, many will conclude that fatigue after training (or better after a long time of intensive training) is related to muscles and that with their recovery exclusively we can fix that problem and carry on. It is not (always) like that. Our body is a very complex system and its parts are arranged by a very clear hierarchy so in any case it makes sense that “it’s all in our heads”.
We come to the term CNS fatigue. What is it and with what kind of training can it occur, what to do when it occurs and a lot of other questions that are related to these kind of problems lie in understanding the connection between muscle systems and CNS.
At first, we will separate training with load towards the goal that we want to achieve to power training and training for hypertrophy. These two forms of training are similar in a lot of things, but in key moments they are very different.
For power training the goal is to make the biggest force possible, while for the training for hypertrophy it is to enlarge the cross section of the muscles, which means to change the appearance.
Unlike power training, for training for hypertrophy the goal is to achieve the feeling of fullness (pump!) with training, and as big micro trauma in the trained muscle (after which “recovery” follows and consequently increase).
CNS has the biggest influence on gaining as much force as possible so a logic conclusion is that with power training will be more busy without parallel (and more prone to fatigue) than with hypertrophy training.
In computer language, power training is directed more towards software improvement (CNS), and hypertrophy training is more turned to hardware development (muscles and support structure).
This can be recognized in practice because every day we meet individuals that don’t have a large muscle mass, but they have achieved an excellent connection between CNS and muscles so they are capable of creating fantastic tension in a large number of muscle fibers simultaneously. This helps them develop great force. So, the more CNS is trained, a bigger number of motor units will be activated.
So, if we know that more muscle fibers are recruited with the bigger weight that we lift, as a logical sequel a reference comes that for power repetition number is 3-5 (or less). Load for power training should be sub maximal, so neuromuscular stimulus could be achieved.
For pump or hypertrophy a slightly smaller loads are needed, but the repetition number is bigger (8-12).
It has always been a dilemma if in one series you should go until the cancellation or not. The answer is: both are right! And how will we know when to go until the cancellation and when not? That depends on a certain exercise. The rule is that if the exercise is more demanding for CNS, you should stop earlier. As opposed to that, with exercises that include CNS in smaller amount, we can go to the cancellation, or even across that border (using various techniques like extended sets, cheating and similar).
Let’s get back to the CNS fatigue. CNS recovers five to six times slower after intense training that muscles that have participated in training. In other words, even though you filled your muscles with glycogen (fuel) and recovered them, CNS (battery) can still be empty or not recovered enough so it could repeat training with the same intensity. The most obvious symptoms of CNS fatigue are lack of motivation, depressive behavior and distorted perception (the feeling that we invest more effort than we actually do).
Let’s look at which exercises are highly exhausting for the CNS, and which are less exhausting:
Very high engagement of the CNS:
Power training (anything above 80% 1RM), Olympic lifting, ballistic (explosive) exercises with maximal intensity, plyometrics with maximal intensity, jumps.
High engagement of the CNS:
Dead lifting and variations, good mornings and variations, all kinds of squats, steps, various thrusts with free weights (overhead press, flat, skew and counter skew thrust on a bench, dips).
Low engagement of the CNS:
Thrust training and pull-backs on the machines, crunches, various insulation exercises for chest, quadriceps, and hamstrings.
Very low engagement of the CNS:
Isolation exercises for biceps, triceps, trapezius, calves and forearms, rope skipping, aerobic training.
If we look for more details in CNS fatigue problems on a micro level, we will find that it depends on some relationships of concrete compounds inside CNS itself. Scientists have discovered what are these compounds so now most of the researches of CNS fatigue are revolve around serotonin and dopamine, because of their role in stress regulation, perception etc.
Research results show that CNS fatigue occurs when it comes to the imbalance of these two neurotransmitters in the brain. Specifically, sudden increase of the serotonin level, and decrease of the dopamine level are responsible for CNS fatigue occurrence. The opposite is also valid: decreased level of serotonin and increased level of dopamine are connected to higher efficiency and better neural drive.
This revelation is more beneficial if we know that we can affect this ratio with the right training plan and with the right diet and supplementation. Right training plan means that we ensure a long enough and quality recovery for our body.
In the field of diet that is connected to the CNS fatigue and recovery, the focus is primarily on BCAA and their effect on the balance of serotonin and dopamine in the brain. BCAA intake suppresses the synthesis of serotonin. The problem is that they also suppress the tyrosine synthesis, which is a precursor of catecholamines that act positively on training quality. However, that problem is easily fixed in a way that together with BCAA we also take tyrosine by supplementation.
Even though in the field of CNS fatigue research a lot has been achieved in understanding the problem, research work is still new and we can expect new useful cognitions that will help us with suppressing (and preventing) this problem.