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Posted: February 10, 2016  :

(IAWR) Athletics: Is Fatigue a Head Game?

Conventional wisdom holds that during running and racing, muscular fatigue is caused by mechanical breakdown. Your cardiovascular system cannot increase the amount of oxygen it supplies, causing the acidity of your blood to increase, which interferes with neuromuscular signalling between your brain and your muscles.

Often compounded by muscles becoming depleted of glycogen (running out of fuel), it becomes impossible for muscles to exert the force necessary to sustain the desired speed. You've hit your limit. Therefore, you must slow down or even cease running.

A problem with this theory is that research studies conclusively show that even though we feel like we cannot run one more step, our leg muscles are nowhere near being maxed out.

What about elite runners? Surely they must be able to max out muscle fibre recruitment to maintain top speed. Not so! According to noted exercise researcher Dr. Tim Noakes: "For in the final stages of any race, perhaps as many as 65% of the muscle fibers in both the leading athletes' legs are inactive and do not contribute to the physical effort". Even though the lead runners are close to exhaustion, they are recruiting not even half of their leg muscle fibres!

Why don't they just recruit a larger percentage of muscles so they can run faster? Can't they issue an internal command like "brain, recruit me more muscle fibres"? Presto, muscle fibres would be activated.

More and more research is showing that fatigue is greatly influenced by your brain and psychological factors that we would not expect to influence what happens mechanically.

Dr. Noakes and colleagues developed the Central Governor Theory to explain how the brain impacts our perception of fatigue. Rather than being caused by events at the muscular level, fatigue is a perception that originates in the brain. Noakes: "Fatigue is simply a sensation the brain invents so you don't overreach yourself". "The human brain is a marvellous but selfish mechanism that reacts to its environment to ensure its survival in the easiest way possible."

In other words, your brain acts like a parent figure, slowing you down in an attempt to protect you from what it perceives as potential harm to yourself.

The brain interprets signals from your entire body, as well as your mental and emotional state. Am I well rested? Am I well trained? How much further do I have to run? Have I run this distance at this pace in the past? Your brain also senses your lack of confidence. Do I really believe I can sustain this pace for the remaining distance of this workout or race? Your brain processes all of these inputs and renders a decision: If the sum of inputs is "positive", your brain programs your body for optimal performance. If the sum of inputs is negative, your brain perceives that you are entering "dangerous" waters, setting into motion physical events at the muscular level that cause you to slow down or pack it in for the day.

Researcher Dr. Samuele Marcora (head of the University of Kent's Endurance Research Group) has conducted extensive research on psychological factors that affect performance. In one experiment, subjects that played video games for 90 minutes before running experienced decreased running performance.

Another study by Dr. Marcora and colleagues, as described in Alex Hutchinson's December 2014 New Yorker article What Is Fatigue?

"As the cyclists pedalled, a screen in front of them periodically flashed images of happy or sad faces in imperceptible sixteen-millisecond bursts, ten to twenty times shorter than a typical blink. The cyclists who were shown sad faces rode, on average, twenty-two minutes and twenty-two seconds. Those who were shown happy faces rode for three minutes longer and reported less of a sense of exertion. In a second experiment, the researchers demonstrated that subliminal action words (GO, LIVELY) could boost a subject's cycling performance by seventeen per cent over inaction words (TOIL, SLEEP)."

Marcora calls his theory a psychobiological model. He believes that you never hit your limits "fatigue is simply a balance between effort and motivation. Physical factors like heat, hydration, muscle conditioning, "are not unreal things, but their effect is mediated by the perception of effort".

Hutchinson concludes: "They (physical factors) don't force you to slow down. They cause you to want to slow down". A very important distinction.

All fine and dandy to read about flashing subliminal smiley faces in laboratory experiments. OR your brain giving you a dose of "parental love" to protect yourself from overexerting.

What can you do to relax your brain's protective grip on your exertion level, push back your perception of effort so you can race closer to your true potential?

Stay tuned next week for tips you can apply to train your brain and run your best.

© 2014 Savvy Runner Inc.

Bennett Cohen and Gail Gould are the Founders and Presidents of the International Association of Women Runners. For access to resources to help you reach your goals for running and racing, visit

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