Can Mental Fatigue Impact Athletic Performance?

Have you ever had a really tough day at work where you did something mentally taxing and then had no energy to go to the gym?

You are not alone.

One of the reasons I prefer to workout in the morning or mid-afternoon is because if I wait till the late afternoon or evening I find I just don’t have the “energy” to train as hard. It is not that my work is physically taxing, so why is my energy drained by the end of the day?

I have been listening to the book Endure by Alex Hutchinson and it turns out mental fatigue can have a huge impact on your physical performance.

In one study, adolescent male endurance athletes were put through both a mentally fatiguing (MF) and non-mentally fatiguing (NMF) task and then had their performance accessed. The NMF task involved reading a magazine for 30 minutes. For the MF task participants had to complete the Stroop task. Here is exactly how the Stroop task was implemented in the study.

Four words (red, blue, green, and yellow) were displayed in a random order on five sheets of A4 paper with 45 words printed on each sheet. Participants were required to verbally respond to each word, with the correct response corresponding to the ink color of the word (red, blue, green, and yellow), rather than the words’ meaning. Therefore, if the word “green” was printed in blue ink, the correct response was “blue”. However, if the ink color of the word was red, the correct response corresponded to the meaning of the word, rather than its printed color. Therefore, if the word “green” was displayed in red ink, the correct answer was “green”. Of note, participants repeatedly read the five sheets over and over for 30 min.

Sounds simple right?

Want to give it a try? Here is an online version, have fun 😉

After participants completed the Stroop task or reading, researches assessed their athletic and cognitive performance. In the MF scenario both physical and cognitive performance decreased when compared to the NMF scenario [1].

So what is the cause of the difference in performance? Is there something physiological that is occurring?

In another study done on cyclists, researchers not only measured performance in a MF state but also physiological parameters like HR, lactate, oxygen consumption and more. In this study cyclists who were MF had a significant decrease in time to exhaustion. However, when researchers looked at physiological measures there were no significant difference between stroke volume, cardiac output, mean arterial pressure, oxygen consumption, and minute ventilation between the MF and NMF groups. The NMF group did have higher heart rates and blood lactate levels at the point of exhaustion when compared to the MF group, but that is likely do to the fact that the NMF group had a greater time to exhaustion[2].

From a physiological perspective, cyclists were not working any harder in a MF state, however it appears that they felt like they were. Their rating of perceived exertion (RPE) in the MF state was significantly higher than in the NMF state.

If the cause of the decreased performance due to MF is not related to anything physiological, what is the root cause?

The answer lies in our brain and has to do with a chemical called adenosine.

During cognitively demanding activities adenosine accumulates in the brain. Adenosine is a chemical that suppresses arousal. In fact, adenosine levels in the brain naturally rise throughout the day in order to promote sleep at night. This is the exact opposite of what we want to happen when we are trying to perform athletically. If adenosine is meant to suppress arousal and promote sleep, it makes sense then why we would not want to exert as much effort physically with higher levels in our brain[3].

As an interesting side note, the reason why caffeine is such a good performance enhancer is because it blocks the adenosine receptors in the brain so we do not feel as fatigued!

What is the takeaway then?

Taper Physically And Mentally

If you are an athlete looking to peak for an event, you would benefit from not only tapering your training but also tapering your mental activity before your event to ensure you are fresh from both a mental and physical point of view.

Incorporate Some Workouts In A Mentally Fatigued State

It is also not necessarily bad to train in a MF state. This type of training is called distressed training. Yes, you may not get the same effect physically from your training because you are not pushing as hard, but from a mental point of view you are training yourself to perform under less than ideal conditions.

This type of training is OK to a point, meaning distress training can start to have negative effects if you overdo it. However, when implemented properly in a training program, it can help build a more resilient athlete and allow you to perform better when things don’t go perfectly.

As you know, I love to look at things from an ancestral perspective, and there is no doubt that our ancestors had days where they were both mentally and physically depleted and had to perform.

Shelters had to be built.

Hunting needed to get done.

Water needed to be carried.

If you didn’t do these things your chances of survival would go down dramatically. Was this our ancestors default state of living?

No, and neither should it be for you.

The trouble I often see in my clients is knowing when to add in distress training to their routines, and this is where I can help. To find out how I can help you become a better athlete, professional, parent, and human you can schedule a discovery call with me by filling out this form.

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  1. (2018, December 3). The Effect of Mental Fatigue on Cognitive and Aerobic … – NCBI. Retrieved October 14, 2020, from
  2. (n.d.). Mental fatigue impairs physical performance in humans …. Retrieved October 14, 2020, from
  3. (2018, June 19). Mental Fatigue Impairs Endurance Performance – Retrieved October 16, 2020, from

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