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Fatigue, Part 5 – The Central Governor Theory

Posted by Scott Christensen



 

The scientific information presented in the first four sections on the onset of fatigue during exercise (Part 1 Fatigue-Energetics, Part 2 Fatigue-Anaerobic Alactic Energy System, Part 3 Fatigue-Anaerobic Glycolytic Energy System, and Part 4 Fatigue-Aerobic Energy System) pointed out the importance of beginning each discussion on energy system metabolism and fatigue with basic knowledge of energetics and the role of energy in muscle contraction.  Discussion of the Central Governor Theory will help tie these sections together.

The accumulation of byproducts or depletion of fuel plays an important role in understanding fatigue.  However, fatigue in a middle distance athlete manifests itself in other ways too.  Fatigue in the nervous system is an important consideration.  Without a voluntary and/or involuntary nerve impulse, a muscle cannot contract. Understanding training considerations for neuromuscular development in middle distance runners plays a prominent role in the programs of coaches like Jacksonville University’s Ron Grigg.

Energy system limitations are the key components in the “peripheral fatigue model” of exercise fatigue.  The skeletal muscle contractions can no longer keep up with the demand of the activity because of fuel depletion or an accumulation of byproduct metabolic waste that is inhibiting the enzyme activity.  Performance deteriorates and eventually exhaustion results. In essence, one part of the body is exhausted, but the other parts are fine.

Fatigue - Part 2: Central Governor Theory, Scott ChristensenThere is another possible explanation of fatigue called the “central fatigue model”.  According to this model, it is proposed that alterations occur within the brain as a direct consequence of exercise.  These alterations typically involve changes in the concentrations of important neuro-transmitters, especially those that are thought to have an inhibitory effect on brain function.  As a result of these alterations, the runner develops the sensations of fatigue, which eventually cause the cessation of exercise. 

This phenomenon is termed the “central governor theory”. 

This theory accounts for something the peripheral fatigue model does not, namely the athlete’s “will” to fight off fatigue even though it is headed toward catastrophic effects to the systems of the body.

The central governor theory suggests that the brain regulates the mass of skeletal muscle that is recruited during running, specifically to ensure that bodily homeostasis is never threatened to the extent of death to the organism.  Accordingly, the key prediction of this model is that the brain acts in “anticipation” to ensure that running is always at an intensity and a volume that does not threaten a catastrophic failure of homeostasis. Middle-distance coaches call this “pace awareness” and it allows racing models to be set up with individual athletes. 

Related Article: Pace Awareness Using Borg’s Ratings of Perceived Exertion (RPE)

For more on setting up highly effective race models, download my free report, ‘Race Tactics & Strategy for the Endurance Events: 800m – 5000m’.

The runner will recruit just enough muscle fibers to match the intensity demand of the workout or race pace.  If the brain is not allowed to do this, fatigue sets in rapidly.  The immediate consequence of a reduced (proper) skeletal muscle recruitment would be reduced muscle work, reduced skeletal blood flow, and as a result a reduced cardiac output.  The central governor model ultimately suggests that while the heart is the slave to the working muscles, at least the brain is there to ensure that the muscles never make excessive demands on the pumping capacity of the heart. 

The central governor theory proposes that the initial pace during exercise is based on prior experience of the average pace that can be sustained for the expected duration of the run.  As a result, an appropriate number of motor units are recruited by the brain in the exercising limbs at the start of the run; more units for higher-intensity running of shorter duration, and less for more prolonged running of lower intensity. Establishing appropriate pace during training is a topic discussed in detail in Session III of my Complete Program Design for HS Middle Distance (800-1600) program. Afferent feedback is sent continually from multiple systems in the body to the brain during running and this produces a continuous modification of the pace that typifies the middle-distance racing model. 

Involuntary and voluntary calculations are made in the brain and efferent commands are relayed to the working muscles in order to complete the required task within the body’s metabolic and mechanical limits.  Wherein lies training theory: improve the metabolic and biomechanical limitations, the commands from the brain adjust the pace, fatigue is delayed, and performance improves.  Studies done on runners in the heat and at altitude show the corresponding work load change that the brain commands as stimuli from the environment is analyzed by the hypothalamus.

The most obvious evidence that the peripheral fatigue model cannot be a singular, absolute predictor of success or failure in performance comes from evidence on how runners pace themselves during races. 

It is obvious that runners do not begin races of 100 meters and 1500 meters at the same pace.  They necessarily begin shorter-distance races at a much higher intensity.  This cannot be explained by the peripheral fatigue model that shows that the pacing strategy is determined exclusively by the action of acidosis in the exercising muscles, or a depletion of fuel in the muscles.  They should start at the same pace in both races if that is the determiner. 

The same can be said about races lasting more than 5 minutes when athletes consistently increase their pace during the final 5-10% of the race when according to the peripheral fatigue theory they should be the most fatigued due to fuel depletion and acidosis.  The peripheral fatigue model cannot explain why athletes can run their fastest pace when fatigue is at its highest point.

These situations are more easily explained by the central governor theory of fatigue working off the experience of training and racing peripheral fatigue.  Experience plays a key physiological role in setting up racing and workout intensities, a fundamental reason I created a program showing you every workout and progression for the entire six month middle distance season. It is the only means for the runner to command the proper motor unit recruitment to get them to the finish line before exhaustion sets in.  

Maximize the efficiency of your athletes’ pacing by downloading my free report: Race Tactics & Strategy for the Endurance Events: 800m – 5000m 

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See also: 

Fatigue, Part 1 – Energetics

Fatigue, Part 2 – Anaerobic Alactic Energy System

Fatigue, Part 3 – Anaerobic Glycolytic Energy System

Fatigue, Part 4 – The Aerobic Energy System

 



Scott Christensen is the head track coach at Stillwater Area High School in Oak Park Heights, MN.

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