Matt Perryman Matt Perryman

How much can the CNS handle? [Stress]

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Awhile back, when I was talking about heavy daily training, I wrote a post about inflammation and how this contributes to the common feeling of ‘overtraining’ (which is probably better termed ‘staleness’). There’s a lot to be said about this topic. I’ve said a lot already, and there’s still plenty more to go.

Overtraining, overreaching, and the interaction between training and the stress response is a blurry area. Relating wider biological concepts, like stress, to specific instances, like workouts and training schedules, is no easy task. Contrary to popular belief, research doesn’t do that. Virtually all of our knowledge on ‘overtraining’ comes from observations in athletes or inference from neurological or biochemical effects.

The term “CNS fatigue” gets name-dropped plenty, and yet you might be surprised how many people truly don’t understand what that term means. CNS fatigue is not a code-word for feeling bad. Properly called central fatigue, this concept can be defined as a reduction in the output of the motor-control regions in the brain, which causes a reduction in performance.

Any time you move, the brain lights up with nerve impulses generated by chemical activity. A stream of these impulses flows from the brain to the working muscles, causing them to contract. We call this flow of nerve impulses ‘central drive’, which we can measure through various methods of arcane science. After some kinds of intense training, we see that central drive is reduced, causing a kind of fatigue even if the muscles are fine.

Neurologist Simon Gandevia has demonstrated that maximum attempts, in the form of sustained maximum contractions (isometrics) and sub-maximal sets-to-failure, both cause a brief drop in central drive. Training near or at maximum levels of output generates fatigue in the central nervous system, which temporarily reduces central drive and thus strength levels. This also affects speed, power, and fine motor control, which leads to sloppiness in highly technical exercises or movements.

Sports scientist Tim Noakes at the University of Cape Town developed the central governor hypothesis to explain this process. According to Noakes, the central governor is a protective mechanism, integrating numerous signals from the body to ensure that we don’t wreck ourselves during a workout. Feelings of fatigue and discomfort during exercise are part of the governor’s control, a behavioral correction that’s supposed to make you stop when you get near the safety margin.

Rather than maximum central drive, it’s the combined effects of muscular fatigue (including the heart), signals of inflammation, and other feedback systems that cause the brain to regulate physical activity within certain safe boundaries.

Noakes goes as far as to suggest that fatigue may be entirely a sensation or emotion, rather than a physical issue:

Hence the novel suggestion is that the conventional understanding of fatigue is flawed because it makes no distinction between the sensation itself and the physical expression of that sensation which, we suggest, is the alteration in the subconsciously regulated pacing strategy consequent on changing motor unit recruitment/derecruitment by the CNS.

When you become fatigued during exercise, your perceived difficulty increases — this is why RPE scores can so accurately determine how tired we are.

The central governor concept is further supported by Lucile Smith’s cytokine hypothesis of overtraining and the cognitive activation theory of stress (CATS) developed by Ursin and Eriksen at the University of Bergen in Norway.

Smith’s cytokine hypothesis suggests a mechanism for tissue trauma and inflammatory markers to trigger sickness behavior in the CNS. This is strikingly similar to Noake’s suggestion of a psychological, rather than physical, fatigue effect. Signals from the body create a neurological response that corresponds with feelings of fatigue.

Ursin and Eriksen suggest that stress is, in part, due to self-sustaining loops between our thoughts and physical stress systems, feedback loops which can be observed in conditions of chronic fatigue and muscle pain. Patients become used to exhaustion or being in pain all the time, and thus their thoughts become focused on exhaustion and pain. This preoccupation actually sensitizes the neural pathways generating the fatigue effect, so much that focusing on the stress makes the stress worse. Again, neurological functions are correlated with thoughts and feelings.

Given the evidence, it seems the central governor is sensitive to fatigue from both power and endurance activities — and that our conscious thoughts can affect it. The mind-over-matter effect can be positive, as with the placebo effect, or it can be negative as suggested by CATS. Our mental state has a very profound effect on the state of our body, in either case.

There are two issues in question. First, does CNS fatigue occur as an inevitable consequence of heavy, near-maximum lifting? That is, are we seeing the brain ‘get tired’, or are we seeing the central governor respond to stress signals from the body (which include our own mental stress)? Second, even if CNS fatigue is unavoidable, is it really the soul-crushing, career-ending bogeyman it’s made out to be (usually by Hardgainer-influenced thinking)?

Let’s get past the urban legends and forum-knowledge to have a real look.

Overtraining: A (Mostly) Mental Problem

After a very heavy workout — heavy as in using weights very close to maximum or setting a PR — it’s normal to feel exhausted. You might feel wiped out, like a dead battery with no juice left. Usually this happens along with feelings of lethargy and lack of motivation.

You’re most likely to experience this after a competition. Those of you who love to train on stimulants and who constantly try to beat last week’s records will be no stranger to burn-out. There’s no question that training to your absolute max at every opportunity is going to wear you down over time. Zatsiorsky called the burn-out of constant maxing ‘staleness’.

Here we run into a terminology issue. What is a ‘maximum’? The Russians defined a 1RM as your best in competition, the absolute best you could achieve on the platform, with all the stress of being in front of a crowd. By some accounts, ‘meet nerves’ could add a spectacular 10% to a lifter’s numbers.

The Bulgarians used a different definition, calling for the best you can do right now, casually. No getting excited, no adrenaline rush, no elevated heart rate. No sitting in the corner brooding over speed metal for 15 minutes before hitting the lift. You just go do it, calm as you can. If you can’t hit it without getting nervous, it’s over your max for the day by definition.

The difference in the two is so substantial that we distinguish between contest maximums (Cmax) and training maximums (Tmax). The dividing line is apprehension. By getting nervous, we switch on the stress response. By treating the lift as a potential threat (nobody wants to get caught under a max squat or bench), we add a new dimension to the problem.

Zatsiorsky acknowledged that staleness comes about largely due to frequent training with Cmax attempts. In comparison, the Tmax (or daily max) represents far less of a stress. Intriguingly, it doesn’t appear to be the weight that burns you out — rather, it’s your response to the weight.

When you recognize that bar sitting on the floor as a maximum deadlift, you get nervous. Stress systems come online, and the central governor knows something’s happening based on that feedback. But if the stress response never happens, will the governor react the same way?

Say it’s not a PR-attempt, but only a pull at 90% of your best-ever deadlift. You could easily argue that a PR is inseparable from getting nervous. But 90%, you should be able to hit that without getting meet-nerves. Will pulling 90%, calm, have the same effect on the central governor?

The common assumption is that lifting anything heavy-enough causes CNS fatigue. Yet there is virtually no evidence to back that belief. So I ask, why must CNS fatigue result from any heavy attempts? Is there any reason to believe this, besides the inertia of tradition? Why must it be the weight, rather than your psychological response to the weight?

I don’t dispute that a true contest maximum will involve psychological arousal and emotional stress. What I believe is that the arrow of causality is reversed. It isn’t that a new record causes CNS fatigue ipso facto; rather, we can’t separate a maximum performance from our own reactions.

I’m suggesting that, in training, we can separate the psychological stress from the physical stress; and with practice, we can learn to fine-tune our psychological reactions to control the stress response. It’s highly unlikely that central fatigue has an on/off switch, as opposed to a sliding scale. If we can learn to minimize the emotional stress, then we can dramatically reduce both the short- and long-term effects of CNS fatigue.

Adaptation to Adaptation

A beginner’s first week in the gym will be marked by extreme soreness. Because we know that this is a short-term effect which will vanish with a few weeks of consistent training, we tell the beginner to ‘deal with it’. The soreness from an exercise bout is temporary and with training it will diminish.

We understand this with muscle. What is it about the CNS and the stress responses that exclude them from the same thought process? As novel stress becomes familiar, so does its effect. Soreness vanishes after repeated sessions. Why wouldn’t CNS fatigue?

Let’s phrase this differently. When you want to adapt your muscles to training, you train them through a period of discomfort. Would it not stand to reason that if you want a robust CNS, you’d train it through a period of discomfort? We’re big on training the muscles to cope, but at the first sign of troubles with the nervous system we run and hide. Should we not train the nervous system as well?

I’ve recently had the chance to read through lecture notes from Ivan Abadjiev, one-time weightlifting coach for the Bulgarian national team and perhaps most widely known for his training system. With its frequent, maximal lifting, Abadjiev’s approach turns conventional strength-training wisdom on its head — and then kicks it a few times for good measure.

Abadjiev suggests that, with repeated exposures, the lifter’s nervous system and stress-response systems (basically the same thing) become better adapted and more tolerant of CNS fatigue. The lifter becomes more adept at ‘turning it on’ to hit a lift, and then turning it back off.

Abadjiev, unlike most, does suggest that we train the nervous system. I’m convinced he’s on to something.

If Noakes is correct about the central governor, that fatigue sensations are separate from genuine physical fatigue, then claims from John Broz about training through the ‘dark times’ become much more believable. The experiences that some of us have had, becoming more and more tolerant of frequent max attempts (to the point of getting almost addicted to daily maxes), can be seen in a new light.

None of this violates the inviolable sage wisdom of the unquestionable gurus of adaptation. It only suggests the one thing which never occurred to them: causing adaptation of the systems that cause adaptation.

We can separate the psychological feel-bad signals of sickness behavior from the genuine physical fatigue that limits performance. Symptoms we normally associate with ‘overtraining’, feelings of lethargy, insomnia, persistent soreness, and lack of motivation, can be seen as the brain telling you to back off. Orthodox wisdom says this is ‘overtraining’ and that you should rest more.

I say we look at the fatigue sensation as psychological DOMS — the symptoms of staleness are the brain’s equivalent of getting sore after a hard workout. Like muscle soreness, it will diminish with training. Like muscle soreness, we can sometimes train through it. And like muscle soreness, sometimes it adds up and we need to take a week off to refresh.

I don’t think anyone would suggest that you can maintain contest-level performances on a regular basis. I’m certainly not saying that. As there are occasions when you are too sore to walk and you might want to take the day off, there will be instances when you are genuinely too burned-out to lift.

My argument in this post is against the all-or-nothing thinking that says you can never and should never train through fatigue. I was stunned that it had never occurred to me to ask ‘why?’ Why shouldn’t I train through it? Well, everbody knows you’ll overtrain if you do that.

There is no conclusive research against the idea, which means you really have to try it for yourself to see what happens. Hardly anyone actually has tried it for themselves, and yet the orthodoxy is so sure that frequent CNS-adaptive training can’t work. I have to wonder why, because the evidence is all circumstantial.


“Whenever you find yourself on the side of the majority, it is time to pause and reflect.”
-Mark Twain

It’s natural to be skeptical of anything flouting the accepted truths. Coming from a more traditional meat-and-potatoes school of thought, hearing that you can thrive by training with maximum lifts every day is like hearing that you can fly by flapping your arms. It just can’t be. Everyone knows that.

Overtraining certainly exists, but the training methods and programming styles that make up the whole of Strength Training Culture will bring you nowhere close to it. What we assume to be ‘overtraining’ is more mythical than real, the teachings of overly-cautious thinkers with more fear than evidence.

My argument comes down to two premises, which I’ll restate here to avoid any confusion:

1. CNS fatigue is not an inevitable consequence of training with near-maximum weights. Psychological arousal is what causes the majority of the ‘overtraining’ symptoms.

If you only trained once a week, you’d expect to get sore after every workout. The CNS reaction is no different, being a kind of ‘mental DOMS’. Training heavy without psychological arousal and learning to be cool under heavy weights causes important adaptations in the nervous system. You can handle heavy lifts without burning yourself out.

2. Feelings of fatigue are separate from genuine physical fatigue. How you feel is a lie, and feeling bad isn’t always an excuse for staying home.

We have a built-in safety margin for performance, and consequently the brain acts to keep us within that boundary to avoid injury. Even though you feel bad, you can still have great workouts. You aren’t ‘overtrained’. While overtraining does exist, it has little to do with short-term feelings of discomfort. Feeling bad, by itself, is not a signal that the body is physically overworked.

The human body doesn’t recover on a workout-to-workout basis, nor is it a fragile antique in grandma’s china cabinet. There is no magical switch that hampers recovery if you train outside your one-hour workout window. You won’t break if you have another workout before you’re ‘fully recovered’. Supercompensation is overrated.

If you look at the origins of the myth, the HIT and Hardgainer schools of thought, they can best be summarized as fear of training hard. You label yourself a genetic handicap and thus have an excuse for failure. Labeling is everything. What you believe about yourself is what you become.

Training through sickness signals doesn’t mean you’ll suffer from overtraining. Believing that you will almost guarantees it. You can literally think yourself into a state of fragility only one set away from collapsing into a pile of rancid overtraining.

I can’t imagine a more poisonous mindset.

Yes, you feel like crap for a few weeks if you train ‘too much’. But you adapt. You get stronger. Work capacity improves. The old cliches about the body — use it or lose it, form follows function — hold true. And since when were we ever guaranteed that lifting weights would be easy and comfortable?

This is not to say that you can step in from day one and squat to a max every day of the week without consequences. Building up the adaptive processes requires time and consistency. You must be patient with your workloads just as you’re patient with strength increases or muscle gains. Even if you aren’t lifting weights every day (and for the record, I think that’s a special case and not a fit for everyone), you can still surprise yourself with what you can handle.

It’s not important to me that I’m ‘right’ about every last piece of trivia. Right is contextual and unimportant. Leave being ‘right’ for the internet experts. Results matter — does it work? Utility matters — can I use this, or any part of this, to improve my own training? From where I stand, the answer to both is ‘yes’.