Fatigue: Why Your Brain Prevents You From Giving Your 100%

You’ve probably heard that playing a sport or overcoming a physical challenge is more of a mental effort than it is a physical one. There may actually be some truth to that.  

Think about fatigue during a hard workout. It’s extremely uncomfortable, often painful, and it makes you feel as though you’ve reached a point from which you just can’t push any harder. However, after reading this article, you will see that you might actually be capable of more than you thought.

Our Brain Limits our Effort

Previous studies proposed that lack of oxygen to working muscles was the cause of fatigue, but newer research suggests that our brain is what is actually responsible for making us feel like throwing in the towel early before we reach a true maximum effort.

Photo Credit: Roxanne King 

What is Fatigue?

Fatigue is defined as an inability to maintain a power output or force during repeated muscle contractions. There are two general components of fatigue: peripheral fatigue and central fatigue.  

Both play a role but the contribution of each type of fatigue appears to be dependent on several different factors, such as the type and intensity of the exercise, the muscles involved, hydration status, mood, knowledge of the duration of the task, the environment, etc.  

Generally peripheral fatigue contributes more in short duration, high intensity activity because it stems from a buildup of metabolic wastes as well as a depletion of the products needed for the muscles fibers to contract.

On the other hand, central fatigue contributes more during lower intensity, endurance activity and has to do with the output from the central nervous system.

This article will focus on central fatigue, as it is most likely more relevant to endurance athletes.

Central Fatigue

The concept of central fatigue is that fatigue occurs when the central nervous system reduces neural drive to the muscles through a reduction in motor unit recruitment and in motor unit firing rate.

In other words, your central nervous system limits your performance by reducing the number and activity of muscle fibers that your body is using at one time.  

The Central Governor Theory

Researchers speculate that a “central governor” mechanism in the central nervous system functions to protect the body from damage.

Dr. Timothy Noakes is well known for his research on the central governor theory. According to Dr. Noakes, fatigue is more like an emotion or a sensation rather than an actual physical event.  

The central nervous system works hard to try to maintain homeostasis by monitoring factors such as hydration, energy reserves, body temperature, and many others to prevent the body from injury.

As you’ll see below, there are many ways these factors can be manipulated to “trick” the brain into increasing motor output.  

Support for the Central Governor Theory

1. Carbohydrate Receptors

A study from 2009 showed that performance increases when athletes rinse their mouths with carbohydrate drinks (but not sugar-free drinks).

This study suggests that receptors inside the mouth indicate to the brain that fuel reserves are being restored (even if nothing makes it through the digestive system) and that it is safe to increase work output.  

2. Swallowing Receptors

Another study showed that even very small amounts of water can increase performance in a dehydrated athlete.

Cyclists who took in 25 ml (less than 2 tablespoons) of water every 5 minutes, were able to ride longer than cyclists who had no water, as well as those who only rinsed their mouth with the water.  

The small amount of water ingested had very little effect on hydration status, but the simple act of swallowing appears to activate receptors in the back of the throat, which send information to the brain and allow exhausting exercise to continue for a longer duration.

3. Heat Deception

One study showed that just knowing what the temperature is outside can decrease performance. This study had 3 groups of cyclists ride in different temperatures: a control group in temperate conditions, and two groups in hot, humid conditions.  

One of the groups in the hot and humid condition was tricked into believing that the ambient temperature and their core temperature were lower than they really were.

The cyclists that were deceived about the riding conditions actually performed as well as the control group. The (incorrect) feedback from the thermometers decreased their rate of perceived exertion and allowed them to push themselves harder.

Take Away

While the Central Governor Theory is still not completely understood, it is certainly something to think about. If you are an endurance athlete, take the studies mentioned into consideration and see if you can use them to your advantage. Some of the tricks to try are swishing your energy drink in your mouth when you don’t have time to drink or are near the end of your event.  Always take small sips of liquid during your ride. Don’t look at the temp before you head out for your ride.

Over to you

Have you tried any of these techniques? Leave a comment below.

Sources:

Arnaoutis, G., S. A. Kavouras, I. Christaki, and L. S. Sidossis. “Water Ingestion Improves Performance Compared with Mouth Rinse in Dehydrated Subjects.” Medicine and Science in Sports and Exercise 44.1 (2012).

Castle, P. C., N. Maxwell, A. Allchorn, A. R. Mauger, and D. K. White. “Deception of Ambient and Body Core Temperature Improves Self Paced Cycling in Hot, Humid Conditions.” European Journal of Applied Physiology 112.1 (2011).

D’Alessio, David, and Luc Tappy. “Oral Carbohydrate Sensing and Exercise Performance.” Current Opinion in Clinical Nutrition & Metabolic Care 13.4 (2010).

Howley, Edward T. Exercise Physiology: Theory and Application to Fitness and Performance. By Scott K. Powers. 8th ed. New York: McGraw-Hill, 2012. 443-45

Noakes, Timothy. “The Central Governor Model in 2012: Eight New Papers Deepen Our Understanding of the Regulation of Human Exercise Performance.” British Journal of Sports Medicine 46.1 (2012).

Nordlund, Maria M., Alf Thorstensson, and Andrew G. Cresswell. “Central and Peripheral Contributions to Fatigue in Relation to Level of Activation during Repeated Maximal Voluntary Isometric Plantar Flexions.” Journal of Applied Physiology 96.1 (2003).

Noakes, Timothy D. “Time to Move beyond a Brainless Exercise Physiology: The Evidence for Complex Regulation of Human Exercise Performance.” Applied Physiology, Nutrition, and Metabolism 36.1 (2011).

Rebecca Gerdon is a student at UNC Chapel Hill studying Exercise and Sport Science and is an NASM certified personal trainer. You can reach her on twitter454545454545454545454545 or check out her blog.