When you get to the end of a workout or a sprint session and fatigue begins to set in, breathing becomes harder, muscles start to burn like they’re on fire, coordination becomes faulty, and you are forced to slow down or even stop.
What is the barrier – what determines fatigue? Is it some physiologic process in your muscles or does fatigue exist elsewhere?
Athletes have long noticed that no matter how tired you are, it’s much easier to overcome fatigue when there is suddenly a chance for you to go on an offensive rush compared to the times when you have to go back and help on defense.
The offensive scenario has a potential reward of scoring, while no such immediate reward exists when back-checking. We are all familiar with trying to overcome fatigue through mental exhortation, such as a coach or an exercise instructor yelling encouragement.
The mental contribution to fatigue has always been known to exist, but recent studies on a diverse range of mental input have shown that this may be the primary factor controlling fatigue.
One study done at Bangor University showed that cyclists were able to overcome fatigue and persist cycling longer when they were shown positive subliminal pictures or phrases compared to a group who were shown negative or discouraging pictures or phrases.
Fatigue was overcome by up to 17 per cent better performance in the ‘positive’ group.
Another set of studies using hydration have also shown how the brain and central nervous system play a decisive role in fatigue.
In one of these studies, the group of cyclists who just rinsed their mouths with (but did not swallow) a carbohydrate drink rode longer compared to the control group, whose members didn’t get the carbohydrate drink.
The study indicates that the taste receptors in the mouth were signaling the brain that it was safe to continue because fuel was being restored, even though no fuel was actually ingested.
An interesting study was also done, once again, on cyclists riding stationary bikes in a climate controlled room while varying heat and humidity.
One group of cyclists rode under normal temperate conditions while two other groups rode at the same elevated temperature and humidity.
The two temperature groups were given feedback about the ambient temperature and their own body’s core temperature.
However, one of the high temperature groups was given incorrect information, making members think that the temperatures were lower than they actually were.
This ‘deceived’ group thus had the same physiologic conditions, but perceived that they were ‘safer’ and had a lower perceived exertion. They performed just as well as the control group, which was exercising at normal temperature and humidity.
The correct-feedback temperature group fatigued and stopped earlier than the other two groups.
The proposed mechanism for this effect is that our perception of fatigue (discomfort, burning muscles) actually originates in the brain as a protective mechanism that keeps the body from getting too close to a life-threatening situation.
This theory, more commonly called the central governor theory, views fatigue as a protective emotion rather than a physiologic, muscular process.
This theory agrees to some extent with a couple of other phenomena we’ve known about for years.
One is that even when we try to maximally contract a muscle to 100% of its capacity, we never achieve 100% of the muscle fibres firing. This has always been viewed as a protective mechanism to avoid muscles from being injured at full ability.
The other phenomenon of brain influence is that when we are injured our brains modify our pain perceptions. If we are fearful, stressed, depressed or otherwise experiencing negative emotions, our brains will amplify pain perception. When we are happier, our brains lower pain perception.
Though not all the mechanisms of the brain’s influence on fatigue and performance are fully understood yet, it appears that the brain plays a dominant, even singular role in fatigue.
Neuroscience is making some amazing discoveries lately and it will be interesting what new developments are in store in the future.
– Kerry Senchyna holds a bachelor of science degree in
kinesiology and is owner of West Coast Kinesiology.
