Mental fatigue affects physical performance

March 2nd, 2009  |  Published in Stumpblog  |  10 Comments

When participants performed a mentally fatiguing task prior to a difficult exercise test, they reached exhaustion more quickly than when they did the same exercise when mentally rested, a new study finds. The study also found that mental fatigue did not cause the heart or muscles to perform any differently. Instead, our “perceived effort” determines when we reach exhaustion. The researchers said the next step is to look at the brain to find out exactly why people with mental fatigue perceive exercise to be more difficult.

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These recent findings, although done in a small group, provide evidence to support a hypothesis advanced by Tim Noakes, the well known author on endurance training, which is that physical fatigue is typically less about mechanical failure (in other words, the tissues themselves say “enough!”) and more about neurological and cognitive failure (in other words, the brain and central/peripheral nervous system say “enough!”).

Responses

  1. Barbara Ling, Virtual Coach says:

    March 2nd, 2009at 2:49 pm(#)

    That is *so* true. I’m in major work mode these days and have found that when my brain finally says ENOUGH, my physical being just wants to shut down too. I’m dealing with that by proactively yanking myself away from work *before* I go into crash-and-burn mode….

  2. Marianna says:

    March 2nd, 2009at 4:17 pm(#)

    Long time lurker, first time poster :o)

    Thanks for posting this – explains a lot. I started training for 2 months now with weights and swimming and have just really been fatigued over the past few weeks and have been reducing my workout times – my research started up again in earnest at the same time. Usually I get a great energy boost from the training, but haven’t had the same feeling since starting back at work. Something to ponder whilst pushing through the fatigue perhaps! Thanks

  3. Sam says:

    March 2nd, 2009at 4:37 pm(#)

    I am the first author of this study, and it does not prove the central governor theory of Tim Noakes. Actually, it disproves it because afferent feedback from the body was not affected by mental fatigue. Thanks for posting it anyway.

  4. Mistress Krista says:

    March 2nd, 2009at 9:31 pm(#)

    Hey! How cool is that! Thanks for posting! Would you care to comment more, Sam?

  5. Sam says:

    March 3rd, 2009at 6:19 am(#)

    The theory of Tim Noakes postulates that the central governor (an unidentified part of our brain which is not proven to exist) regulates exercise performance based on afferent sensory feedback from muscles, heart and lungs and, for time trials and competitions, knowledge of the end point.

    In my study the physiological status and function of muscles, heart and lungs were not affected, therefore sensory feedback to the alleged central governor should have been the same and, consequently, central governor regulation of performance should have been the same.

    The fact that performance is reduced in my study proves that primary disturbances of the brain can limit performance. There is no need for a central governor in the brain. Our conscious brain is more than enough!

  6. Mistress Krista says:

    March 3rd, 2009at 6:24 am(#)

    Very helpful elaboration! Thanks so much.

  7. Ingrid Wren says:

    March 7th, 2009at 1:44 am(#)

    This is so interesting. My husband and I have just returned from competing at a European Dancesport Championship, followed by some days snow skiing. We travelled from Tasmania, Australia, to Helsinki, Finland, and back again. Straight back to work, which for me is very intense these days (and a months worth of work to catch up on), and trying to get back into a regular training/fitness routine has almost defeated us. We have both been fatigued and incredibly tired…

    This discussion explains a lot. We have also been gathering information in order to renovate our kitchen and going through the processes for that, which is turning out to be pretty intense. No wonder we are struggling! Our brains must be overloaded and our bodies are following suit.

    More sleep perhaps? What are your recommendations?

  8. Sat, Mar 14th – CrossFit Ireland - Great People. Great Fitness. says:

    March 13th, 2009at 6:48 pm(#)

    [...] Mental Fatigue Affects Physical Performance [...]

  9. Tim Noakes says:

    June 23rd, 2009at 2:33 pm(#)

    Sam is not entirely correct to say that his study disproves the Central Governor Model. We both believe that the brain regulates exercise performance. Sam believes that this is due to conscious controls; we believe that it can be due to conscious controls but also to subconscious controls. As an ultradistance runner I learned that it was never possible for me to speed up until the final 1-2 km of a 90km race however much I might consciously have wanted to (between say 60 and 88km). All my conscious effort was necessary to insure that I did not slow down; it was impossible to speed up. Sam’s model cannot explain why it is impossible to speed up whenever you simply want to. We think this is because the subconscious controls are acting. We do not understand how conscious controls alone can explain how the body regulates its internal environment with exquisite accuracy during exercise across a wide range of environmental conditions.

    We have supplied evidence that exercise performance cannot be explained solely by conscious controls – for example exposure to heat or low oxygen air produces changes in exercise performance that have to be due to sensory feedback to the brain. For how does the brain know how hot it is or how low is the oxygen content of the air without somehow measuring its effects on the body? Or how does a low blood glucose concentration or low muscle glycogen content impair exercise performance without the subconscious brain being the source of that information?

    My colleague who is an expert in the subconscious mind once said that if the actions of the subconscious brain were not subconscious there would be no room for conscious thoughts. They would simply be crowded out by all that is going on in the subconscious brain.

    The idea that the subconscious plays no part in the regulation of exercise would not seem to be entirely probable.

  10. Mistress Krista says:

    June 23rd, 2009at 2:53 pm(#)

    Fascinating elaboration, and it raises a variety of new questions! So essentially you are suggesting that we are looking at a system that, with adequate effort, can mostly just inhibit degradation rather than augment performance? (In other words, we should consider not going slower, rather than going faster, as the improvement — because our default would be to slow down?)


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