Is Fatigue All in Your Head?

Rowing - USA Lwt 4 @ World Champs 2003
Why do these guys look tired?

I just heard of a new series of studies (hat tip to Diane Jacobs) which provide a very good example of how the brain acts as a central governor on physical performance.*

For a long time, research on the causes of muscle fatigue have focused exclusively on changes in the muscle itself, while ignoring the fact that the brain has control over whether the muscle can contract. More recently, researchers such as Tim Noakes have been advancing the idea that the brain acts as a governor on muscle performance. The idea is that the brain makes you feel tired as a way to prevent you from the dangers of overexertion. In other words, when your muscles fail, it’s not because they can’t “just do it”, it’s because the brain just won’t let them do it.

A recent series of studies has identified some of the neural processes that are responsible for implementing the central governor. Here is a brief summary of the findings.

In one study, researchers showed that motor commands to engage in intense exercise eventually create a sensory feedback loop that inhibits those same commands. It goes like this. The primary motoric area of the brain tells the muscles to contract repeatedly. This results in sensory signalling from the body that is read by parts of the brain that act to inhibit the primary motoric area from continuing with the contractions.

This is very similar to the process by which pain inhibits muscular activity. Which is not surprising, since both pain and excessive muscle activity are a potential threat to the body. In each case, the brain elects to protect against the threat by essentially shutting down the ability to continue with the threatening activity – in this case, repeated contraction of tired muscles.

Researchers were able to determine through the use of a functional MRI that right before muscle failure, the areas of the brain that became more active were the thalamus and insular cortex, two areas that analyze information indicating a threat to the body. Another study confirmed that the insular cortex is in fact the area that inhibits the primary motoric area.

Another study showed that pain medication which blocks feedback from the body also prevents the muscular inhibition that comes from fatigue.

Put these findings all together and a simple picture merges. When the brain receives information from the body indicating that a particular form of exertion is a threat, it decides to shut the activity down. It is surprising to me that such a common sense idea takes so long to gain acceptance, and is ignored all too often.

This dovetails very well with a central principle of training recommended on this blog (which is also one of the basic ideas in Z-Health): threat not only causes pain, it limits performance. If you want to increase performance, work to reduce threat.

This is why the “no pain no gain” mentality of exercise is so counterproductive, and why giving the brain “good news” about the body should be a primary training strategy.

Let me know what you think in the comments.

*I have been meaning to finish my series on central governors, which will include a more extensive discussion of the theories of Tim Noakes. Not sure when I will get to that though. 

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17 Responses to Is Fatigue All in Your Head?

  1. Great post. So how does this “giving the brain “good news” about the body” apply to bodywork? Have you run in to any research? Does the no pain no gain principle work the same in bodywork as well?

    • Ross,

      I like to think of all beneficial forms of exercise, mobilizing, stretching or bodywork as giving the brain good news about the body. The news is basically that: “Its safe to do this”, or “here’s a useful movement option that you may have forgotten.”

      When you lift more weight, run further, stretch further, or move faster than you normally do, WITHOUT eliciting pain or stress, the brain gets good news about the state of the body. In the context of a massage, the news might simply be that it doesn’t hurt to move here or sense something here, or get pressure here. Make sense?

  2. Interesting observation; i couldn’t agree more with your finding, that the take-away from understanding neural underpinnings of muscle fatigue should be to reduce threat in order to increase performance, rather than to medicate symptoms and push through the pain.

  3. Todd,

    Interesting indeed, and not at all surprising, since, as you said, fatigue is very similar to pain. The are both conscious experiences, which means they are output, not input. Fatigue and pain are active constructs of the brain.

    This has very interesting implications for chronic fatigue.

    It also explains why some patients, e.g. post surgery, are very very tired. Probably more than their bodies ‘really’ are. But very protective: fatigue changes your behaviour in a health promoting way (that is, post surgery): you take it easy.

    Very much like pain, fear of movement and mood changes: adaptive in acute phase, maybe not so on the longer run.

    • Pieter,

      Interesting points about chronic fatigue and post surgery recovery. I suspect continued research in this area may lead to many other insights into the connections between fatigue and health.

  4. This research would seem to contradict those who have adopted a HIT approach to strength training. Granted the volume and frequency with this type of training are quite low, but the intensity can be very high.

    Would you have any suggestions for alternate strength training methods?

    • Brent,

      Thanks for commenting. I don’t think this invalidates a HIT approach or any other form of intense exercise that causes threat. It just means that you have to be wary of the amount of the threat. You can’t increase your strength or fitness unless you put the body under some degree of threat – that is what starts the body adapting to deal with the threat by getting stronger, fitter, etc. All training involves some form of threat innoculation. But just as with a vaccine, you need the right dose – not too much not too little. And threat comes in many forms and can accumulate.

      So my suggestion for strength training is to create enough stress and threat to cause an adaptation but not too much to cause injury and prevent recovery. And make sure training doesn’t cause pain, because this will make the difference between too much and too little too hard to find.

  5. Thanks for the article! I wonder how this would apply to sports that are meant to hurt, like middle-distance or marathon running or cross-country skiing. Does the same principal apply to cardiovascular exertion?

    • Max,

      I hope those sports weren’t meant to hurt.

      I think the relevance to those sports and to any form of exertion or stress is that the hurting and the fatigue is the brain’s way of protecting the body because of it senses a threat from the exertion. There’s nothing wrong with putting the body under threat, that is how we get fit. You just need to make sure the dose of threat is in the right amount – not too much not too little.

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