What Really Controls Fatigue?

by Mitch Hauschildt, MA, ATC, CSCS

Recently I read some really interesting and convincing information on what really controls fatigue in the body during physical exertion.  I was taught in school that most of the time fatigue is caused by lack of ATP or Oxygen and/or a build up of byproducts within the tissue (i.e. Lactic Acid).  I was taught that physical fatigue is a metabolic issue.

That explanation makes a lot of sense on a basic and rudimentary level when we look at the mechanical make up of the tissue and specifics systems.  But, in my mind, it doesn’t really explain how all of the various effects come together to create fatigue in the system.  Why is it that if I speak a certain way to my athletes in the midst of a game or workout I can get a better outcome?  If their fatigue is only due to metabolic factors, how can that be overcome when someone wants to? Also, we know that things like stress, lack of sleep, mood, and environment (i.e. heat, cold, playing surface) all play important roles with regard to our levels of fatigue during physical activities.  These things can’t be completely attributed to a lack of ATP or build up of byproducts.

The most logical explanation in this conversation is the nervous system.  I am now a much stronger believer that the brain can and does throttle down activities to protect the body overall.  As I mentioned, I was recently reading some work by Tim Noakes on the Central Governor Theory and I believe that it’s foundation makes a lot of sense with regards to how we generally manage physical fatigue, whether we realize it or not.

What Noakes says is the the brain is constantly monitoring every system in the body.  And, because it is set up merely for survival, it will throttle things down and put a governor on the overall system to avoid a catastrophic event.  A catastrophe could be something like heat illness or a major musculoskeletal injury that could occur under duress or extreme conditions.  In order to prevent these injuries or illnesses, the brain pulls back on the amount of output that the body can actually exert to protect it.

It is also thought to do this because the brain also wants to be prepared for something unexpected and have a reserve of energy.  If you think about our brain in survival mode, if you were stuck in the wilderness and were tired and fatigued from trying to find your way home and suddenly a wild animal jumped out of the bushes and you had no energy reserves, you would die quickly.  Rather than letting you die, the brain keeps an energy reserve just for that situation.

While there is some controversy as to whether this theory actually holds water, my opinion is that it makes a lot of sense.  The major criticism to Noakes’ theory is that if the brain does this, then why do we see catastrophes occur, such as heat illness and injuries when you get tired?  If the brain monitors everything closely and makes calculations, then how would those things ever take place.  I believe that there are 2 ways that catastrophic events still occur:

• The brain doesn’t have great control over the body and it’s systems for many people, even when they are fresh.  Honestly, this happens all the time.  People have crappy movement patterns because their brain doesn’t own the body the way that we would like it to.  We have to reset the system to get the body out of the default patterns to get it to move more cleanly.  In the case of a heat illness for example, the body may be trying to monitor things closely, but it likely miscalculates how efficient (or inefficient) the system is.  That means that body heat is allowed to rise more quickly than the brain anticipates that it should and before you know it, it is past the point of no return.  This is why people who are deconditioned are much more likely to have issues than those who are fit.  The brain can’t predict things nearly as efficiently without practice.  Like many things in life, small little miscalculations compound themselves into big problems.
• A person can essentially “override” the governor if they want to badly enough.  You see it all of the time with high end athletes.  They are trained well and know how and where they can push their system.  They feel the governor coming on and they choose to mentally override it.  The world of sports psychology can do great things for performance here, but can also expose people to injury if it isn’t handled well.

Overall, the Central Governor Theory is just that…a theory.  So, there will continue to be some debate as to its existence and role.  But, knowing what I know about the body and nervous system, I personally think it makes a ton of sense and sheds some light on where we should be spending our training time.

Training and conditioning will do great things to help the brain calculate safe loads and refine it’s ability to predict loads.  It will also help it feel safe in stressful situations, which is really the ultimate goal.  The less safe the brain feels, the more likely it is to push back.  Train it, make it safe, make it fun.  The results will come.