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The conventional wisdom is that tiredness is something that happens to muscles. However, research suggests that your brain and central nervous system play a far greater role in the perception of fatigue than previously recognised. Andrew Hamilton investigates and explains the implications for the way you train…
Ireland is a marvellous place to spend some time. Friendly people, breathtaking scenery and Guinness to die for! However, should you wish to cycle across its green and pleasant landscape, beware of large dogs, which emerge without warning from front gardens at lightening speed, baring gleaming white teeth and snapping inches away from your heels.
It was during one of these high-speed sprints to escape the snarling jaws of a particularly humongous Alsatian that I stumbled across a truth that broke all the conventional rules of exercise physiology. Having covered 70 hard rain-soaked miles into a headwind, I was almost unable to spin the cranks, yet when the ‘hound from hell’ gave chase, I suddenly found myself accelerating at warp factor 9 to easily outsprint him until his bark could be heard no more!
The intriguing question therefore is this: If fatigue occurs as a result of physical and chemical changes in the muscles doing the work, for example running out of ‘fuel’ or a build-up of fatiguing lactate, why is it that when you’re extremely fatigued, you can suddenly summon up phenomenal amounts of extra energy when required?
This approach proposes that there are three main causes of fatigue, all of them biochemical in nature:
The chemical approach to fatigue (see panel 1) explains how fatigue arises in terms of biochemistry. However, if it’s a real description of what happens when we feel fatigue, how do we explain the following?:
A number of exercise physiologists and psychologists now believe that while the physiological status and feedback from the muscles is important, the brain and its information processing plays a large role in determining how we feel during exercise. For example, we know that if you tell a cyclist that they’re going to cycle distance ‘x’ then later suddenly tell them that the ride is going to be shorter than they thought, they tend to experience a drop in their perceived level of exertion. Conversely, if you announce the ride will be longer, fatigue increases. According to the chemical approach, simply changing someone’s expectations of a workout dramatically changes muscle biochemistry but this is clearly nonsense!
Originally proposed by professor of exercise physiology and running guru Tim Noakes, the thrust of the central governor theory is that the brain uses a mixture of conscious, sub-conscious and physiological cues to control the muscles and hold them back from reaching the true brink of exhaustion.
In other words, physiological factors (such as the level of muscle glycogen, lactate etc) are not the direct cause of fatigue, but just some of many signals that the brain takes into account along with other information, to set the level of fatigue you actually experience. According to the theory, the brain is constantly monitoring the situation and when it decides you’ve had enough, it creates the distressing sensations you then interpret as muscle fatigue.
In evolutionary terms, central governor theory makes sense; your ‘central governor’ (brain) is constantly monitoring both your body and its environment to ensure there’s always something left in case of an emergency so you can respond quickly to an unexpected threat. It also helps to explain a number of other phenomena. For example, in a study on interval training, researchers took a group of cyclists and assigned them to a 4-week interval-training program [3]. Despite the fact they completed only six interval sessions, the cyclists were able to shave an average of two minutes off their 40-kilometer time trial performance.
According to the chemical theory, this improvement is down to changes in the muscles that make them better at using oxygen, which in turn makes them more able to fight fatigue. In the above study however, these changes occurred extremely rapidly and Noakes believes that part of how interval-training works is by teaching the central governor that going faster won’t do your body any harm.
Further evidence that the brain plays a major role in determining perceptions of fatigue comes from caffeine; a lot of research has demonstrated that caffeine can enhance both endurance and shorter duration, high-intensity exercise performance by reducing the perception of fatigue [4,5]. Much of the initial speculation was that caffeine exerted its effects by enhancing energy production, in particular fat burning. However, more recent research points strongly to that fact that the fatigue-beating effects of caffeine are in fact due to its ability to stimulate the central nervous system and block receptors in the brain that are associated with feelings of fatigue [6]. Likewise, there’s been much recent research into the effects of music and exercise performance, showing that music can increase time to exhaustion and reduce feelings of fatigue [7,8].
How can you apply central governor theory to enhance your own training? Here are a few tips based on the theory, which should make your training more productive and enjoyable:
References
1. Journal of Experimental Biology, 204, 3225-3234, 2001
2. American Journal of Physiology, R281, 187-196, 2001
3. Medicine and Science in Sports and Exercise, 28, 1427-1434, 1996
4. Conlee, R.K. 1991. Amphetamine, caffeine, and cocaine. In: Perspectives in Exercise Science and Sports Medicine, Volume 4: Ergogenics—Enhancement of Performance in Exercise and Sport, pp. 285–330. Lamb, D.R., andWilliams, M.H. (Eds.). Dubuque, IA:Wm.C. BrownPublishers
5. Spriet, L.L. 2000. Caffeine. In: Performance-Enhancing Substances in Sport and Exercise, pp. 267–278. Bahrke, M.S., and Yesalis, C.E. (Eds.) Champaign, IL: Human Kinetics
6. Am J Physiol Regul Integr Comp Physiol 284: R399-R404, 2003
7. Percept & Motor Skills 83, 1347-1352, 1996
8. J of Sport Behavior 20, 54-68, 1997
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