Monday, April 13, 2009

Mental fatigue impairs physical performance in humans

I just finished an interview with the fine folks at I will give you all a heads up once the interview is posted. In it I discuss more mobility fun, why static stretching sucks, and much more.

Mental Fatigue Impairs Performance
Here is something that I have wondered about for years, but until recently never found any data.

When I started working in Technical Services for a major medical device company after my first 7.5 years in college many years ago in a galaxy far far away, I would get grilled all day answering calls from patients, reps, nurse and doctors. They ranged from Ethel that was too close to her microwave and she was trying to hide around the corner closing the door with a broomstick (microwaves and pacemakers are not an issue) to a physician at a device implant who is calling about a certain feature and you can hear the monitors in the background beeping.

I could not understand why I was so tired once I got home even though I sat no my butt all day! Part of this was from just not moving around much at all, but perhaps part of it was "mental fatigue"?

On to the Study
The nice part was the study below was a crossover design, so each subject acted as their own control. This allows you to use less subjects overall as you are only comparing 2 different conditions changes; so one with mental fatigue and the other without.

While it has been argued that a bike to exhaustion is not similar to a time trial format, the vast majority of evidence has been collected using that format. Time trials can be altered too by the subjects (esp. non competitive athletes) learning to pace themselves better.

The performance decrease did not appear to be from the heart/lungs (cardiorespiratory) or muscles! It appears to be all in your head indeed!

If anyone has watched lots of exercise tests to exhaustion will tell you, you need to be very careful what you say to them during a test. I always make it a point to explain everything up front and remind them that it is a max test. Once the test is over half way, I only use encouragement and do not give one group an "option" to quit. My guess is that if someone is working very hard (RPE of a 9 out of 10) and you reminded them that they can stop at any point now because the test is on a volunteer basis, many would just stop even though physically their numbers may be the same!

Other trials have attempted to get around this by giving money for the top performance to make it more competitive.

No mater how you cut it, endurance events at a high level are much about pain management.

Thoughts on the study? Let me know by posting a comment
Rock on
Mike T Nelson

Mental fatigue impairs physical performance in humans

Samuele M. Marcora, Walter Staiano, and Victoria Manning School of Sport, Health and Exercise Sciences, Bangor University, Bangor, Wales, United Kingdom Submitted 4 October 2008 ; accepted in final form 5 January 2009

Mental fatigue is a psychobiological state caused by prolonged periods of demanding cognitive activity. Although the impact of mental fatigue on cognitive and skilled performance is well known, its effect on physical performance has not been thoroughly investigated. In this randomized crossover study, 16 subjects cycled to exhaustion at 80% of their peak power output after 90 min of a demanding cognitive task (mental fatigue) or 90 min of watching emotionally neutral documentaries (control). After experimental treatment, a mood questionnaire revealed a state of mental fatigue (P = 0.005) that significantly reduced time to exhaustion (640 ± 316 s) compared with the control condition (754 ± 339 s) (P = 0.003).

This negative effect was not mediated by cardiorespiratory and musculoenergetic factors as physiological responses to intense exercise remained largely unaffected. Self-reported success and intrinsic motivation related to the physical task were also unaffected by prior cognitive activity. However, mentally fatigued subjects rated perception of effort during exercise to be significantly higher compared with the control condition (P = 0.007). As ratings of perceived exertion increased similarly over time in both conditions (P < style="font-weight: bold;">

CONCLUSION: In conclusion, our study provides experimental evidence that mental fatigue limits exercise tolerance in humans through higher perception of effort rather than cardiorespiratory and musculoenergetic mechanisms. Future research in this area should investigate the common neurocognitive resources shared by physical and mental activity.