How Your Own Brain Is Making You Run Slowly and What You Can Do About It

By Josh Adams

You don’t give 100% when you run. Your brain is involuntarily keeping your body from hurting itself with exertion. It never lets you hit your physical performance limit. Science has good evidence that this is how fatigue occurs in endurance sports.

Fatigue as a Mental Calculation

Exercise science used to hold to peripheral fatigue theory. It states that you decrease your physical exertion when your muscles get tired. But it has problems.

The biggest is that as runners approach the finish line they are often able to produce a burst of additional speed to cross it. This is seen in races of 800 meters or more. It doesn’t jibe with peripheral fatigue because if the athlete’s muscles are exhausted then proximity to the finish line should not affect their performance.

In the 1990s an exercise scientist named Tim Noakes overthrew the prevailing wisdom. He posited the central governor theory of fatigue. Noakes thought that the brain unconsciously regulates exercise performance. It attempts to prevent exertion-caused damage to the body. It makes calculations about how fast and far a runner can safely go.

The term “central governor” has fallen from favor since there is not one physical area in your brain that is solely responsible for this effect. The preferred name is now anticipatory regulation of fatigue though it is sometimes called the psychobiological model of fatigue. The idea remains the same.

As you approach this mentally-imposed performance limit your brain makes you feel awful. Each moment seems an unbearable eternity. Excuses for stopping come readily to mind. You will slow down well before the physical need arrives.

This is often seen to be true because after running stops it can be resumed with even greater intensity almost immediately. The “need” to stop was a mirage. While you are experiencing this agony your brain will decrease your muscle activation against your will. So willpower can’t override anticipatory regulation.

Your brain is an amazing effort calculator. There are many factors in the calculations, including the distance yet to be run, motivation to persevere, heart rate, oxygen consumption, lactate threshold, core body temperature, muscle fatigue, and so on. Thus it’s not accurate to say that fatigue is only mental, clearly the body is an input.

The brain seems to combine all of these inputs into a single value that becomes the best predictor of athletic performance: the Rating of Perceived Exertion (RPE). In short, the more effort you feel you are exerting, the shorter the time your brain will allow you to maintain that pace.

Is This Mental Fatigue Stuff New Age Junk?

Don’t just take it from me. Some of the best evidence for the brain’s role in endurance involves studies of muscle contractions. Exercise scientists have compared quadriceps contractions controlled by the brain versus magnetic stimulation. They measure the force of muscle tightening in an athlete by both methods before and after riding on a stationary bike. This allows them to compare the physical and mental contributions to fatigue.

With rested muscles the external stimulation produced contractions 17% stronger than the voluntary ones. But with fatigued muscles the magnetically-caused contractions were 29% stronger than the normal contractions. The brain is clearly unable to fully use the muscles as fatigue occurs.

Now That is fatigue!

The worst part is that your brain’s anticipatory regulation system will slow you down before the physiological fatigue starts. This has been shown in studies with subjects on stationary bicycles in hot rooms. The riders would slow their pace from the very beginning of the exercise. This happened before their muscles were fatigued and their core body temperature approached the safety limit.

Your brain’s anticipatory regulation can be manipulated in other ways too. Thermostats that are rigged to give a cooler room temperature in warm rooms produce improved performance on stationary bicycles. Rinsing your mouth with sugar water and spitting it out gives your brain the sensation that it has more fuel. Your brain in turn allows the body more effort.

Even feelings of anger, smiling, swearing, and false information about the duration of exercise can trick the brain into allowing the body to push itself harder. Also it appears that certain drugs, such as Wellbutrin and acetaminophen (AKA Tyelonol) can effect the brain’s anticipatory regulation.

Smiling can reduce the perceived exertion of runners.

Subliminal messaging on-screen while cyclists performed “time to failure” trials on stationary bikes has fooled the brain too. Riders shown happy faces or “action words” can pedal for longer than those shown sad faces or “inaction words”. Maybe there is a market for a Google Glass app for runners that does some subliminal messaging.

What Can You Do About It?

All of this goes to show that endurance has a huge mental component. Perceptions, feelings, and beliefs matter for athletic performance. The question is, how should this knowledge affect the way in which you train?

Fortunately, this has been written about by smarter people than myself. Matt Fitzgerald in How Bad Do You Want It and RUN: The Mind-Body Method of Running By Feel and Alex Hutchinson in his book Which Comes First, Cardio or Weights and the Sweat Science blog on Runners World cover it more thoroughly.

They have done an excellent job of digesting the technical scientific research of others and explaining it in a way that a layperson can understand. What follows are a few of their thoughts.

  • Train yourself to better withstand suffering. You should be pushing yourself hard enough on some training runs to experience serious suffering. In fact, experiencing as much misery as you expect to feel during your race is the goal. Exposure to this misery will increase your tolerance for it. This gradually gives your anticipatory regulation system a new baseline for perceived effort.
  • Make your performance personally significant. The more important an event is to you the more agony you will be willing to take. Carefully choose some key races and workouts and elevate their significance. Runners can usually go faster in races than in training because they are seen as the culmination of all their hard work.
  • Set concrete performance goals. Having clear goals can also increase your capacity to exert yourself. As Fitzgerald points out, “There is no such thing as exercising as hard as you can.” Goals can create an anchoring effect for your brain to take into account with its calculations.
  • Get real time performance feedback. On days where you are running faster than expected you can see your good time and use it to spur yourself onward to a PR. Matt Fitzgerald gives a great example of a demonstration he gave at a CrossFit presentation. He had a volunteer hold a dumbbell at shoulder height with arm outstretched for as long as possible. Then Matt had him do the same thing with his non-dominant arm. This time he told him the duration of the first attempt and he updated him on his elapsed time. With the real time feedback he kept the weight up longer.
  • Assess your mental toughness after runs. Did you ever go slower than necessary to reduce suffering? Write this down in journal or spreadsheet and monitor it over time. The power of writing things down cannot be overstated.
  • Perform in front of an audience and compete with other runners when training. Studies have shown that performing for an audience and competition with other athletes can increase endurance. Since the presence of spectators or competitors doesn’t cause physiological changes, this is obviously a mental hack.
  • Learn to find enjoyment in tough runs that result in improved performance. Steadily getting better at something through hard work can be enjoyable despite the self-torture. It is important to realize that suffering and fun can happen together. People are willing to exert themselves more at things they enjoy doing. Enjoyment makes misery itself more tolerable as has been shown in studies involving exercising mice and chocolate.
  • Perform mental exercises before going on a training run. This can help train you to handle mental fatigue during endurance exercise without having to add the wear and tear to your body in order to induce that mental fatigue. This often involves 90 minutes of tedious mental attention on computers.
  • Brace yourself for pain during runs. Sometimes athletes look beyond their next race toward other goals and expect to breeze through what is thought to be a routine outing. When they encounter greater than expected suffering this can cause them to have reduced tolerance for it.


Improving running performance requires training of your body and mind. Even though fatigue is controlled by the brain you cannot override it with willpower. “Mind over matter” fails because anticipatory regulation is largely unconscious. Instead, you can gradually teach your brain what your body is safely capable of doing through deliberately training to suffer.

Happy miserable running!

For further reading you might want to start with Alex Hutchinson’s article What Is Fatigue? in the New Yorker.

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