Exercise is one of the biggest challenges to the continuous functioning of our body—also known as homeostasis. When we exercise, we wear down tissues, spend calories, consume nutrients, and basically threaten the integrity of our bodies. That’s not a problem: the human body has been designed and built by the creative errors of evolution to be a high-performance athletic machine. And this machine comes with a regulatory mechanism whose purpose it is to ensure that our homeostasis does not become compromised by athletic activity: the “central governor.”

Although this may be obvious to some, it is news to the majority of exercise physiologists, and it is still being debated by cutting-edge researchers. What can you say? Old ideas die hard.

The classical model of exercise stated that the reason we became fatigued was because more and more muscle fibers were being “poisoned” by the by-products of exercise, and could no longer function. This is what most of us were taught in gym class. This model proposes that exercise continues at a steadily decreasing pace as more and more systems become impaired and fail. When taken to its extreme, this culminates in a “catastrophe” where the body’s homeostasis breaks down, and we experience a generalized systems failure: death. Because of that, it is commonly referred to as the “catastrophe” model of human physiology.

On the other hand we have the model that Timothy Noakes and others endorse: the “complexity” model of human physiology. This model suggests that there is a “central governor” in the brain, responsible for regulating athletic output. The central governor uses past, present and future data from internal and external sources to determine the maximum amount of muscle fibres it is safe to recruit during muscle contractions. In order for you to stay conscious during exercise, the concentration of nutrients and oxygen in the blood must be above a certain threshold. For example, if your blood-oxygen concentration drops below 30 mm Hg, you will lose consciousness. The brain has to regulate the body’s use of oxygen, as well as all the other fuels: it’s not just a matter of who consumes what amount of fuel. If the muscles are consuming fuel too fast (regardless of whether they are tired), the blood concentration of those fuels will drop below their critical threshold. The system which the brain employs to control that consumption is the central governor.

This is exactly what we see: one of the most important observations by Noakes and St. Clair Gibson was that states of crippling fatigue occur long before the body nears organ or system failure, and before blood oxygen falls below the levels necessary to sustain consciousness. Because of this, the complexity model sees fatigue less as a symptom of physiological damage and more as a neural mechanism designed to prevent that physiological damage:

“The presence of homoeostasis in all organ systems at the point of exhaustion is perhaps the most robust evidence supporting the hypothesis that exercise performance is regulated centrally in the brain as part of a complex dynamic system.”

— Noakes, St. Clair Gibson, Lambert (2005).

In effect, the central governor creates feelings of fatigue to prevent us from consciously pushing our bodies far enough that we take ourselves into a state of systemic failure. Along those lines, it has been found that our muscles are never “recruited” to their full extent for any single contraction. During prolonged exercise, it has been shown that only about 30% of muscle fibers are used. We can increase the proportion of muscle fibers recruited by making a greater effort—and by doing so we move even more quickly towards fatigue.

Furthermore, this model helps us to explain and understand one of the most common athletic phenomena: pacing. If our speed becomes reduced solely because our muscles are becoming poisoned, and fatigue is simply a side-effect, then we shouldn’t have a way of knowing how to regulate our speed. In fact, we shouldn’t be able to regulate our speed; the quality of everyone’s perfomance during a race should steadily decrease at the same pace. Also, we shouldn’t be able to sprint to the finish line; it would be mechanically impossible for our muscles to increase their output if the only reason it decreased was because they were being poisoned. Contrary to this, we see that more experienced athletes—in particular those with knowledge of a certain course—finish with better times, and pace themselves more consistently throughout the race.

Let’s listen to our bodies as we train and race. Let’s not forget the central governor. It’s trying to tell us something. Let’s not block out its messages with our iPods—and then be surprised when we become injured. Let’s ask “why?” instead. In true systems-thinking fashion, let’s not fight the system, but instead use the attributes of the system itself to catapult us into greater and safer levels of performance.